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First_Aid_Step1. “Biochemistry is the study of carbon compounds that crawl.” “We think we have found the basic mechanism by which life comes from life.” —Francis H. C. Crick “The biochemistry and biophysics are the notes required for life; they conspire, collectively, to generate the real unit of life, the organism.” This high-yield material includes molecular biology, genetics, cell biology, and principles of metabolism (especially vitamins, cofactors, minerals, and single-enzyme-deficiency diseases). When studying metabolic pathways, emphasize important regulatory steps and enzyme deficiencies that result in disease, as well as reactions targeted by pharmacologic interventions. For example, understanding the defect in Lesch-Nyhan syndrome and its clinical consequences is higher yield than memorizing every intermediate in the purine salvage pathway.


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First_Aid_Step1. Do not spend time learning details of organic chemistry, mechanisms, or physical chemistry. Detailed chemical structures are infrequently tested; however, many structures have been included here to help students learn reactions and the important enzymes involved. Familiarity with the biochemical techniques that have medical relevance—such as ELISA, immunoelectrophoresis, Southern blotting, and PCR—is useful. Review the related biochemistry when studying pharmacology or genetic diseases as a way to reinforce and integrate the material. H1 histone (linker) Supercoiled structure Heterochromatin Euchromatin Metaphase chromosome Nucleosome (H2A, H2B, H3, H4) 2 DNA DNA double-helix DNA exists in the condensed, chromatin form to fit into the nucleus. DNA loops twice around a histone octamer to form a nucleosome (“beads on a string”). H1 binds to the nucleosome and to “linker DNA,” thereby stabilizing the chromatin fiber.


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First_Aid_Step1. Phosphate groups give DNA a ⊝ charge. Lysine and arginine give histones a ⊕ charge. In mitosis, DNA condenses to form chromosomes. DNA and histone synthesis occurs during S phase. Mitochondria have their own DNA, which is circular and does not utilize histones. Heterochromatin Condensed, appears darker on EM (labeled H HeteroChromatin = Highly Condensed. in A ; Nu, nucleolus). Sterically inaccessible, Barr bodies (inactive X chromosomes) may be thus transcriptionally inactive. • methylation, visible on the periphery of nucleus. • acetylation. Histone methylation Usually causes reversible transcriptional Histone Methylation Mostly Makes DNA Mute. suppression, but can also cause activation depending on location of methyl groups. Histone acetylation Removal of histone’s ⊕ charge  relaxed DNA Histone Acetylation makes DNA Active. coiling  transcription. Histone deacetylation Removal of acetyl groups  tightened DNA coiling • transcription.


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First_Aid_Step1. Histone deacetylation Removal of acetyl groups  tightened DNA coiling • transcription. Nucleotides NucleoSide = base + (deoxy)ribose (Sugar). NucleoTide = base + (deoxy)ribose + phosphaTe; linked by 3′-5′ phosphodiester bond. PURines (A,G)—2 rings. PYrimidines (C,U,T)—1 ring. Deamination reactions: Cytosine  uracil Adenine  hypoxanthine Guanine  xanthine 5-methylcytosine  thymine Uracil found in RNA; thymine in DNA. Methylation of uracil makes thymine. Purine (A, G) Pyrimidine (C, U, T) 5′ end of incoming nucleotide bears the triphosphate (energy source for the bond). Triphosphate bond is target of 3′ hydroxyl attack. PURe As Gold. CUT the PY (pie). Thymine has a methyl. C-G bond (3 H bonds) stronger than A-T bond (2 H bonds).  C-G content  melting temperature of DNA. “C-G bonds are like Crazy Glue.” purr until they GAG): Glycine Aspartate Glutamine


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First_Aid_Step1. De novo pyrimidine Various immunosuppressive, antineoplastic, and antibiotic drugs function by interfering with and purine synthesis nucleotide synthesis: (de novo requires aspartate, Glutamine + CO2 glycine, glutamine, and THF) Lefunomide 6-MP, Mycophenolate,(impaired in Pyrimidine synthesis: Leflunomide: inhibits dihydroorotate dehydrogenase 5-fluorouracil (5-FU) and its prodrug capecitabine: form 5-F-dUMP, which inhibits thymidylate synthase ( dTMP) Purine synthesis: 6-mercaptopurine (6-MP) and its prodrug azathioprine: inhibit de novo purine synthesis Mycophenolate and ribavirin: inhibit inosine monophosphate dehydrogenase Purine and pyrimidine synthesis: • Hydroxyurea: inhibits ribonucleotide reductase AMP GMP • Methotrexate (MTX), trimethoprim (TMP), and pyrimethamine: inhibit dihydrofolate reductase (• deoxythymidine monophosphate [dTMP]) in humans, bacteria, and protozoa, 5-FU, MTX, TMP, pyrimethamine


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First_Aid_Step1. MTX, TMP, pyrimethamine ADA, adenosine deaminase; APRT, adenine phosphoribosyltransferase; HGPRT, hypoxanthine guanine phosphoribosyltransferase; XO, xanthine oxidase. Defective purine salvage due to absent HGPRT, which converts hypoxanthine to IMP and guanine to GMP. Results in excess uric acid production and de novo purine synthesis. X-linked recessive. Findings: intellectual disability, self-mutilation, aggression, hyperuricemia (orange “sand” [sodium urate crystals] in diaper), gout, dystonia, macrocytosis. Treatment: allopurinol or febuxostat (2nd line). HGPRT: Hyperuricemia Gout Pissed off (aggression, self-mutilation) Retardation (intellectual disability) DysTonia Unambiguous Each codon specifies only 1 amino acid. Commaless, Read from a fixed starting point as a continuous Exceptions: some viruses. nonoverlapping sequence of bases. Universal Genetic code is conserved throughout Exception in humans: mitochondria. evolution.


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First_Aid_Step1. Universal Genetic code is conserved throughout Exception in humans: mitochondria. evolution. DNA replication Eukaryotic DNA replication is more complex than in prokaryotes but uses many enzymes analogous to those listed below. In both prokaryotes and eukaryotes, DNA replication is semiconservative, involves continuous and discontinuous (Okazaki fragment) synthesis, and occurs in the 5′  3′ direction. B Y-shaped region along DNA template where leading and lagging strands are synthesized. C Unwinds DNA template at replication fork. Helicase Halves DNA. Deficient in Bloom syndrome (BLM gene mutation). Single-stranded Prevent strands from reannealing. binding proteins F Makes an RNA primer on which DNA polymerase III can initiate replication. H Prokaryotes only. Degrades RNA primer; Same functions as DNA polymerase III, also replaces it with DNA. excises RNA primer with 5′  3′ exonuclease.


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First_Aid_Step1. H Prokaryotes only. Degrades RNA primer; Same functions as DNA polymerase III, also replaces it with DNA. excises RNA primer with 5′  3′ exonuclease. I Catalyzes the formation of a phosphodiester Joins Okazaki fragments. bond within a strand of double-stranded DNA. Ligase Links DNA. Mutations in DNA Severity of damage: silent << missense < nonsense < frameshift. Types of single nucleotide (point) mutations: • Transition—purine to purine (eg, A to G) or pyrimidine to pyrimidine (eg, C to T). Transversion—purine to pyrimidine (eg, A to T) or pyrimidine to purine (eg, C to G). Single nucleotide substitutions Silent mutation Nucleotide substitution codes for same (synonymous) amino acid; often base change in 3rd position of codon (tRNA wobble). Missense mutation Nucleotide substitution results in changed amino acid (called conservative if new amino acid has similar chemical structure). Examples include sickle cell disease (substitution of glutamic acid with valine).


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First_Aid_Step1. Nonsense mutation Nucleotide substitution results in early stop codon (UGA, UAA, UAG). Usually results in nonfunctional protein. Stop the nonsense! Other mutations Frameshift mutation Deletion or insertion of a number of nucleotides not divisible by 3 • misreading of all nucleotides downstream. Protein may be shorter or longer, and its function may be disrupted or altered. Examples include Duchenne muscular dystrophy, Tay-Sachs disease. Splice site mutation Retained intron in mRNA • protein with impaired or altered function. Examples include rare causes of cancers, dementia, epilepsy, some types of β-thalassemia, Gaucher disease, Marfan syndrome. Lac operon Classic example of a genetic response to an environmental change. Glucose is the preferred metabolic substrate in E coli, but when glucose is absent and lactose is available, the lac operon is activated to switch to lactose metabolism. Mechanism of shift:


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First_Aid_Step1. Low glucose  adenylate cyclase activity  generation of cAMP from ATP  activation of catabolite activator protein (CAP) • transcription. High lactose  unbinds repressor protein from repressor/operator site • transcription. Binds CAP site, Lacl LacZ LacY LacACAP site Promoter Operator Repressor protein Lacoperon Bindsoperator, blockstranscription organization of a eukaryotic gene Exon Intron Exon Intron Exon Regulation of gene expression Silencer DNA locus where regulatory proteins (“repressors”) bind, decreasing expression of a gene on the same chromosome. Initial transcript is called heterogeneous nuclear RNA (hnRNA). hnRNA is then modified and becomes mRNA. The following processes occur in the nucleus: Capping of 5′ end (addition of 7-methylguanosine cap) Polyadenylation of 3′ end (≈ 200 As) Splicing out of introns Capped, tailed, and spliced transcript is called mRNA. mRNA is transported out of nucleus to be translated in cytosol.


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First_Aid_Step1. Polyadenylation of 3′ end (≈ 200 As) Splicing out of introns Capped, tailed, and spliced transcript is called mRNA. mRNA is transported out of nucleus to be translated in cytosol. mRNA quality control occurs at cytoplasmic processing bodies (P-bodies), which contain exonucleases, decapping enzymes, and microRNAs; mRNAs may be degraded or stored in P-bodies for future translation. Poly-A polymerase does not require a template. AAUAAA = polyadenylation signal. Eukaryotes RNA polymerase I makes rRNA, the most common (rampant) type; present only in nucleolus. RNA polymerase II makes mRNA (massive), microRNA (miRNA), and small nuclear RNA (snRNA). RNA polymerase III makes 5S rRNA, tRNA (tiny). No proofreading function, but can initiate chains. RNA polymerase II opens DNA at promoter site. I, II, and III are numbered in the same order that their products are used in protein synthesis: rRNA, mRNA, then tRNA.


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First_Aid_Step1. I, II, and III are numbered in the same order that their products are used in protein synthesis: rRNA, mRNA, then tRNA. α-amanitin, found in Amanita phalloides (death cap mushrooms), inhibits RNA polymerase II. Causes severe hepatotoxicity if ingested. Actinomycin D, also called dactinomycin, inhibits RNA polymerase in both prokaryotes and eukaryotes. Prokaryotes 1 RNA polymerase (multisubunit complex) Rifampin inhibits DNA-dependent RNA makes all 3 kinds of RNA. polymerase in prokaryotes. Splicing of pre-mRNA Part of process by which precursor mRNA (pre-mRNA) is transformed into mature mRNA. Alterations in snRNP assembly can cause clinical disease; eg, in spinal muscular atrophy, snRNP assembly is affected due to  SMN protein  congenital degeneration of anterior horns of spinal cord  symmetric weakness (hypotonia, or “floppy baby syndrome”). Primary transcript combines with small nuclear ribonucleoproteins (snRNPs) and other proteins to form spliceosome.


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First_Aid_Step1. Primary transcript combines with small nuclear ribonucleoproteins (snRNPs) and other proteins to form spliceosome. RNA polymerases P P OOH 3˜OH 3˜Cleavage at 5˜splice site; lariat-shaped (loop) intermediate is generated. Cleavage at 3˜splice site; lariat is released to precisely remove intron and join 2 exons. Exon 1 Exon 2 Spliceosome+P UGAAG3˜Exon 1 Mature mRNA Exon 2 P UGAAG


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First_Aid_Step1. Structure 75–90 nucleotides, 2º structure, cloverleaf form, anticodon end is opposite 3′ aminoacyl end. All tRNAs, both eukaryotic and prokaryotic, have CCA at 3′ end along with a high percentage of chemically modified bases. The amino acid is covalently bound to the 3′ end of the tRNA. CCA Can Carry Amino acids. T-arm: contains the TΨC (ribothymidine, pseudouridine, cytidine) sequence necessary for tRNAribosome binding. T-arm Tethers tRNA molecule to ribosome. D-arm: contains Dihydrouridine residues necessary for tRNA recognition by the correct aminoacyltRNA synthetase. D-arm allows Detection of the tRNA by aminoacyl-tRNA synthetase. Attachment site: the 5′-CCA-3′ is the amino acid acceptor site.


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First_Aid_Step1. Charging Aminoacyl-tRNA synthetase (uses ATP; 1 unique enzyme per respective amino acid) and binding of charged tRNA to the codon are responsible for the accuracy of amino acid selection. Aminoacyl-tRNA synthetase matches an amino acid to the tRNA by scrutinizing the amino acid before and after it binds to tRNA. If an incorrect amino acid is attached, the bond is hydrolyzed. A mischarged tRNA reads the usual codon but inserts the wrong amino acid. 3. eIFs released when the mRNA and the ribosomal 60S subunit assemble with the complex. Requires GTP. Aminoacyl-tRNA binds to A site (except for initiator methionine, which binds the P site), requires an elongation factor and GTP. rRNA (“ribozyme”) catalyzes peptide bond formation, transfers growing polypeptide to amino acid in A site. Ribosome advances 3 nucleotides toward 3′ end of mRNA, moving peptidyl tRNA to P site (translocation). ATP—tRNA Activation (charging). GTP—tRNA Gripping and Going places (translocation).


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First_Aid_Step1. Ribosome advances 3 nucleotides toward 3′ end of mRNA, moving peptidyl tRNA to P site (translocation). ATP—tRNA Activation (charging). GTP—tRNA Gripping and Going places (translocation). Think of “going APE”: A site = incoming Aminoacyl-tRNA. P site = accommodates growing Peptide. E site = holds Empty tRNA as it Exits. Termination Eukaryotic release factors (eRFs) recognize the stop codon and halt translation • completed polypeptide is released from ribosome. Requires GTP. Trimming Removal of Nor C-terminal propeptides from zymogen to generate mature protein (eg, trypsinogen to trypsin). Covalent alterations Phosphorylation, glycosylation, hydroxylation, methylation, acetylation, and ubiquitination. Chaperone protein Intracellular protein involved in facilitating and maintaining protein folding. In yeast, heat shock proteins (eg, HSP60) are expressed at high temperatures to prevent protein denaturing/misfolding.


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First_Aid_Step1. Cell cycle phases Checkpoints control transitions between phases of cell cycle. This process is regulated by cyclins, cyclin-dependent kinases (CDKs), and tumor suppressors. M phase (shortest phase of cell cycle) includes mitosis (prophase, prometaphase, metaphase, anaphase, telophase) and cytokinesis (cytoplasm splits in two). G1 and G0 are of variable duration. GO G1Growth DNASynthesis INTERPHASERb, p53 modulate Grestriction point G2 M CytokinesisS Mitosis Site of synthesis of secretory (exported) proteins and of N-linked oligosaccharide addition to lysosomal and other proteins. Nissl bodies (RER in neurons)—synthesize peptide neurotransmitters for secretion. Free ribosomes—unattached to any membrane; site of synthesis of cytosolic, peroxisomal, and mitochondrial proteins. Mucus-secreting goblet cells of the small intestine and antibody-secreting plasma cells are rich in RER. Proteins within organelles (eg, ER, Golgi bodies, lysosomes) are formed in RER.


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First_Aid_Step1. Mucus-secreting goblet cells of the small intestine and antibody-secreting plasma cells are rich in RER. Proteins within organelles (eg, ER, Golgi bodies, lysosomes) are formed in RER. Cell trafficking Golgi is distribution center for proteins and lipids from ER to vesicles and plasma membrane. Posttranslational events in Golgi include modifying N-oligosaccharides on asparagine, adding O-oligosaccharides on serine and threonine, and adding mannose-6-phosphate to proteins for lysosomal trafficking. Endosomes are sorting centers for material from outside the cell or from the Golgi, sending it to lysosomes for destruction or back to the membrane/Golgi for further use.


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First_Aid_Step1. I-cell disease (inclusion cell disease/mucolipidosis type II)—inherited lysosomal storage disorder (autosomal recessive); defect in N-acetylglucosaminyl-1-phosphotransferase  failure of the Golgi to phosphorylate mannose residues ( mannose-6-phosphate) on glycoproteins  proteins are secreted extracellularly rather than delivered to lysosomes. Results in coarse facial features, gingival hyperplasia, clouded corneas, restricted joint movements, claw hand deformities, kyphoscoliosis, and high plasma levels of lysosomal enzymes. Often fatal in childhood. Key: Abundant, cytosolic ribonucleoprotein that traffics polypeptide-ribosome complex from the cytosol to the RER. Absent or COPI dysfunctional SRP  accumulation of protein in cytosol. trans COPI: Golgi  Golgi (retrograde); cis-Golgi Anterograde • ER. COPII: ER • cis-Golgi (anterograde).


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First_Aid_Step1. trans COPI: Golgi  Golgi (retrograde); cis-Golgi Anterograde • ER. COPII: ER • cis-Golgi (anterograde). Golgi apparatus “Two (COPII) steps forward (anterograde); one (COPI) step back (retrograde).” Clathrin: trans-Golgi • lysosomes; plasma membrane • endosomes (receptormediated endocytosis [eg, LDL receptor Rough activity]). endoplasmic reticulum Peroxisome Membrane-enclosed organelle involved in: β-oxidation of very-long-chain fatty acids (VLCFA) (strictly peroxisomal process) α-oxidation of branched-chain fatty acids (strictly peroxisomal process) Catabolism of amino acids and ethanol Synthesis of cholesterol, bile acids, and plasmalogens (important membrane phospholipid, especially in white matter of brain) Zellweger syndrome—autosomal recessive disorder of peroxisome biogenesis due to mutated PEX genes. Hypotonia, seizures, hepatomegaly, early death.


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First_Aid_Step1. Refsum disease—autosomal recessive disorder of α-oxidation  phytanic acid not metabolized to pristanic acid. Scaly skin, ataxia, cataracts/night blindness, shortening of 4th toe, epiphyseal dysplasia. Treatment: diet, plasmapheresis. Adrenoleukodystrophy—X-linked recessive disorder of β-oxidation due to mutation in ABCD1 gene  VLCFA buildup in adrenal glands, white (leuko) matter of brain, testes. Progressive disease that can lead to adrenal gland crisis, coma, and death. Proteasome Barrel-shaped protein complex that degrades damaged or ubiquitin-tagged proteins. Defects in the ubiquitin-proteasome system have been implicated in some cases of Parkinson disease. Cytoskeletal elements A network of protein fibers within the cytoplasm that supports cell structure, cell and organelle movement, and cell division.


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First_Aid_Step1. Cytoskeletal elements A network of protein fibers within the cytoplasm that supports cell structure, cell and organelle movement, and cell division. Cylindrical outer structure composed of a helical array of polymerized heterodimers of αand β-tubulin. Each dimer has 2 GTP bound. Incorporated into flagella, cilia, mitotic spindles. Grows slowly, collapses quickly. Also involved in slow axoplasmic transport in neurons. Molecular motor proteins—transport cellular cargo toward opposite ends of microtubule. REtrograde to microtubule (+  −)—DYnein. Anterograde to microtubule (−  +)—Kinesin. Clostridium tetani, herpes simplex virus, poliovirus, and rabies virus use dynein for retrograde transport to the neuronal cell body. Drugs that act on microtubules (Microtubules Get Constructed Very Poorly): Paclitaxel (anticancer) Negative end Near Nucleus. Positive end Points to Periphery. REaDY? AttacK! Cilia structure 9 doublet + 2 singlet arrangement of microtubules


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First_Aid_Step1. Paclitaxel (anticancer) Negative end Near Nucleus. Positive end Points to Periphery. REaDY? AttacK! Cilia structure 9 doublet + 2 singlet arrangement of microtubules A . Basal body (base of cilium below cell membrane) consists of 9 microtubule triplets B with no central microtubules. Axonemal dynein—ATPase that links peripheral 9 doublets and causes bending of cilium by differential sliding of doublets. Gap junctions enable coordinated ciliary movement. Kartagener syndrome (1° ciliary dyskinesia)— immotile cilia due to a dynein arm defect. Autosomal recessive. Results in  male and female fertility due to immotile sperm and dysfunctional fallopian tube cilia, respectively; of ectopic pregnancy. Can cause bronchiectasis, recurrent sinusitis, chronic ear infections, conductive hearing loss, and situs inversus (eg, dextrocardia on CXR C ). nasal nitric oxide (used as screening test). (Kartagener’s restaurant: take-out only; there’s no dynein “dine-in”.)


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First_Aid_Step1. nasal nitric oxide (used as screening test). (Kartagener’s restaurant: take-out only; there’s no dynein “dine-in”.) Na+-K+ ATPase is located in the plasma membrane with ATP site on cytosolic side. For each ATP consumed, 3 Na+ leave the cell (pump phosphorylated) and 2 K+ enter the cell (pump dephosphorylated). Plasma membrane is an asymmetric lipid bilayer containing cholesterol, phospholipids, sphingolipids, glycolipids, and proteins. Pumpkin = pump K+ in. Ouabain (a cardiac glycoside) inhibits by binding to K+ site. Cardiac glycosides (digoxin and digitoxin) directly inhibit the Na+-K+ ATPase, which leads to indirect inhibition of Na+/Ca2+ exchange • [Ca2+]i  cardiac contractility. Cleavage of procollagen Cand N-terminals Formation of cross-links (stabilized by lysyl oxidase) Collagen fber


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First_Aid_Step1. Synthesis—translation of collagen α chains (preprocollagen)—usually Gly-X-Y (X and Y are proline or lysine). Collagen is 1⁄3 glycine; glycine content of collagen is less variable than that of lysine and proline. Hydroxyproline is used for lab quantification of collagen. Hydroxylation—hydroxylation of specific proline and lysine residues. Requires vitamin C; deficiency • scurvy. Glycosylation—glycosylation of pro-α-chain hydroxylysine residues and formation of procollagen via hydrogen and disulfide bonds (triple helix of 3 collagen α chains). Problems forming triple helix • osteogenesis imperfecta. Exocytosis—exocytosis of procollagen into extracellular space. Proteolytic processing—cleavage of disulfide-rich terminal regions of procollagen insoluble tropocollagen. Cross-linking—reinforcement of many staggered tropocollagen molecules by covalent lysine-hydroxylysine cross-linkage (by copper-containing lysyl oxidase) to make collagen fibrils. Problems with cross-linking


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First_Aid_Step1. Menkes disease. Genetic bone disorder (brittle bone disease) caused by a variety of gene defects (most commonly COL1A1 and COL1A2). Most common form is autosomal dominant with  production of otherwise normal type I collagen. Manifestations include: Multiple fractures and bone deformities after minimal trauma (eg, during birth) B due to the translucent connective tissue over choroidal veins Some forms have tooth abnormalities, including opalescent teeth that wear easily due to lack of dentin (dentinogenesis imperfecta) May be confused with child abuse. Treat with bisphosphonates to  fracture risk. Patients can’t BITE: Faulty collagen synthesis causing hyperextensible skin A , hypermobile joints B , and tendency to bleed (easy bruising). Multiple types. Inheritance and severity vary. Can be autosomal dominant or recessive. May be associated with joint dislocation, berry and aortic aneurysms, organ rupture. Hypermobility type (joint instability): most common type.


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First_Aid_Step1. Hypermobility type (joint instability): most common type. Classical type (joint and skin symptoms): caused by a mutation in type V collagen (eg, COL5A1, COL5A2). Vascular type (fragile tissues including vessels [eg, aorta], muscles, and organs that are prone to rupture [eg, gravid uterus]): mutations in type III procollagen (eg, COL3A1). X-linked recessive connective tissue disease caused by impaired copper absorption and transport due to defective Menkes protein (ATP7A, vs ATP7B in Wilson disease). Low copper levels (vs high levels in Wilson disease). Leads to  activity of lysyl oxidase (copper is a necessary cofactor) • defective collagen. Results in brittle, “kinky” hair, growth retardation, hypotonia, • risk of cerebral aneurysms.


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First_Aid_Step1. Elastin Stretchy protein within skin, lungs, large arteries, elastic ligaments, vocal cords, ligamenta flava (connect vertebrae  relaxed and stretched conformations). Rich in nonhydroxylated proline, glycine, and lysine residues, vs the hydroxylated residues of collagen. Tropoelastin with fibrillin scaffolding. Cross-linking takes place extracellularly and gives elastin its elastic properties. Broken down by elastase, which is normally inhibited by α1-antitrypsin. α1-Antitrypsin deficiency results in unopposed elastase activity, which can cause COPD. Changes with aging:  dermal collagen and elastin,  synthesis of collagen fibrils; cross-linking remains normal. Marfan syndrome—autosomal dominant (with variable expression) connective tissue disorder affecting skeleton, heart, and eyes. FBN1 gene mutation on chromosome 15 (fifteen) results in defective fibrillin, a glycoprotein that forms a sheath around elastin. Findings: tall with long extremities; pectus carinatum (more specific)


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First_Aid_Step1. FBN1 gene mutation on chromosome 15 (fifteen) results in defective fibrillin, a glycoprotein that forms a sheath around elastin. Findings: tall with long extremities; pectus carinatum (more specific) or pectus excavatum A ; hypermobile joints; long, tapering fingers and toes (arachnodactyly); cystic medial necrosis of aorta; aortic root aneurysm rupture or dissection (most common cause of death); mitral valve prolapse. Subluxation of lenses, typically upward and temporally (vs downward and medially in homocystinuria).


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First_Aid_Step1. Polymerase chain Molecular biology lab procedure used to amplify a desired fragment of DNA. Useful as a diagnostic reaction tool (eg, neonatal HIV, herpes encephalitis). Denaturation—DNA is heated to ~95°C to separate the strands. Annealing—Sample is cooled to ~55°C. DNA primers, a heat-stable DNA polymerase (Taq), and deoxynucleotide triphosphates (dNTPs) are added. DNA primers anneal to the specific sequence to be amplified on each strand. Elongation—Temperature is increased to ~72°C. DNA polymerase attaches dNTPs to the strand to replicate the sequence after each primer. Heating and cooling cycles continue until the DNA sample size is sufficient.


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First_Aid_Step1. Heating and cooling cycles continue until the DNA sample size is sufficient. CRISPR/Cas9 A genome editing tool derived from bacteria. Consists of a guide RNA (gRNA) , which is complementary to a target DNA sequence, and an endonuclease (Cas9), which makes a single-or double-strand break at the target site . Break imperfectly repaired by nonhomologous end joining (NHEJ)  accidental frameshift mutations (“knock-out”) , or a donor DNA sequence can be added to fill in the gap using homology-directed repair (HDR) . Not used clinically. Potential applications include removing virulence factors from pathogens, replacing disease-causing alleles of genes with healthy variants, and specifically targeting tumor cells. Southern blot 1. DNA sample is enzymatically cleaved into smaller pieces, which are separated on a gel by electrophoresis, and then transferred to a filter. 2. Filter is exposed to radiolabeled DNA probe that recognizes and anneals to its complementary strand.


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First_Aid_Step1. 2. Filter is exposed to radiolabeled DNA probe that recognizes and anneals to its complementary strand. 3. Resulting double-stranded, labeled piece of DNA is visualized when filter is exposed to film. Northern blot Similar to Southern blot, except that an RNA sample is electrophoresed. Useful for studying DRoP: mRNA levels, which are reflective of gene Southern = DNAexpression. Northern = RNAWestern blot Sample protein is separated via gel electrophoresis Western = Protein and transferred to a membrane. Labeled antibody is used to bind to relevant protein. Southwestern blot Identifies DNA-binding proteins (eg, c-Jun, c-Fos [leucine zipper motif]) using labeled double-stranded DNA probes.


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First_Aid_Step1. Southwestern blot Identifies DNA-binding proteins (eg, c-Jun, c-Fos [leucine zipper motif]) using labeled double-stranded DNA probes. Flow cytometry Laboratory technique to assess size, granularity, and protein expression (immunophenotype) of individual cells in a sample. Cells are tagged with antibodies specific to Commonly used in workup of hematologic abnormalities (eg, leukemia, paroxysmal nocturnal hemoglobinuria, fetal RBCs in mother’s blood) and immunodeficiencies (eg, CD4+ cell count in HIV). Fluorescent label Antibody Anti-CD3 Ab Laser makes label fuoresce Laser Detector 104 103 Anti-CD8 Ab Fluorescence is detected; labeled cells are counted Cell surface or intracellular proteins. Antibodies are then tagged with a unique fluorescent dye. Sample is analyzed one cell at a time by focusing a laser on the cell and measuring light scatter and intensity of fluorescence.


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First_Aid_Step1. Data are plotted either as histogram (one measure) or scatter plot (any two measures, as shown). In illustration: Cells in left lower quadrant ⊝ for both CD8 and CD3. CD8-expressing cells also express CD3. Cells in left upper quadrant ⊕ for CD3 and 100 ⊝ for CD8. 100 101 102 103 104 CD8 CD8 and CD3. and ⊝ for CD3. In this example, right lower quadrant is empty because all Microarrays Thousands of nucleic acid sequences are arranged in grids on glass or silicon. DNA or RNA probes are hybridized to the chip, and a scanner detects the relative amounts of complementary binding. Used to profile gene expression levels of thousands of genes simultaneously to study certain diseases and treatments. Able to detect single nucleotide polymorphisms (SNPs) and copy number variations (CNVs) for a variety of applications including genotyping, clinical genetic testing, forensic analysis, cancer mutations, and genetic linkage analysis.


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First_Aid_Step1. Karyotyping Colchicine is added to cultured cells to halt chromosomes in metaphase. Chromosomes are stained, ordered, and numbered according to morphology, size, arm-length ratio, and banding pattern (arrows in A point to extensive abnormalities in a cancer cell). Can be performed on a sample of blood, bone marrow, amniotic fluid, or placental tissue. Used to diagnose chromosomal imbalances (eg, autosomal trisomies, sex chromosome disorders). Fluorescent DNA or RNA probe binds to specific gene site of interest on chromosomes (arrows in A point to abnormalities in a cancer cell, whose karyotype is seen above; each fluorescent color represents a chromosome-specific probe). Used for specific localization of genes and direct visualization of chromosomal anomalies at the molecular level. Microdeletion—no fluorescence on a chromosome compared to fluorescence at the same locus on the second copy of that chromosome.


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First_Aid_Step1. Microdeletion—no fluorescence on a chromosome compared to fluorescence at the same locus on the second copy of that chromosome. Translocation—fluorescence signal that corresponds to one chromosome is found in a different chromosome (two white arrows in A show fragments of chromosome 17 that have translocated to chromosome 19). Duplication—a second copy of a chromosome, resulting in a trisomy or tetrasomy (two blue arrows show duplicated chromosomes 8, resulting in a tetrasomy). Molecular cloning Production of a recombinant DNA molecule in a bacterial host. Steps: 1. Isolate eukaryotic mRNA (post-RNA processing) of interest. 2. Add reverse transcriptase (an RNA-dependent DNA polymerase) to produce complementary DNA (cDNA, lacks introns). 3. Insert cDNA fragments into bacterial plasmids containing antibiotic resistance genes. 4. Transform (insert) recombinant plasmid into bacteria. 5. Surviving bacteria on antibiotic medium produce cloned DNA (copies of cDNA).


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First_Aid_Step1. 4. Transform (insert) recombinant plasmid into bacteria. 5. Surviving bacteria on antibiotic medium produce cloned DNA (copies of cDNA). Cre-lox system Can inducibly manipulate genes at specific developmental points (eg, to study a gene whose deletion causes embryonic death). RNA interference Process whereby small non-coding RNA molecules target mRNAs to inhibit gene expression. Codominance Both alleles contribute to the phenotype of the Blood groups A, B, AB; α1-antitrypsin heterozygote. deficiency; HLA groups. Variable expressivity Patients with the same genotype have varying 2 patients with neurofibromatosis type 1 (NF1) phenotypes. may have varying disease severity. Anticipation Increased severity or earlier onset of disease in Trinucleotide repeat diseases (eg, Huntington succeeding generations. disease). Presence of genetically distinct cell lines in the same individual.


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First_Aid_Step1. Presence of genetically distinct cell lines in the same individual. Somatic mosaicism—mutation arises from mitotic errors after fertilization and propagates through multiple tissues or organs. Gonadal mosaicism—mutation only in egg or sperm cells. If parents and relatives do not have the disease, suspect gonadal (or germline) mosaicism. McCune-Albright syndrome—due to Gs-protein activating mutation. Presents with unilateral café-au-lait spots A with ragged edges, polyostotic fibrous dysplasia (bone is replaced by collagen and fibroblasts), and at least one endocrinopathy (eg, precocious puberty). Lethal if mutation occurs before fertilization (affecting all cells), but survivable in patients with mosaicism. Locus heterogeneity Mutations at different loci can produce a similar Albinism. phenotype. Allelic heterogeneity Different mutations in the same locus β-thalassemia. produce the same phenotype.


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First_Aid_Step1. Locus heterogeneity Mutations at different loci can produce a similar Albinism. phenotype. Allelic heterogeneity Different mutations in the same locus β-thalassemia. produce the same phenotype. Heteroplasmy Presence of both normal and mutated mtDNA passed from mother to all children. mtDNA, resulting in variable expression in mitochondrially inherited disease. Uniparental disomy Offspring receives 2 copies of a chromosome from 1 parent and no copies from the other parent. HeterodIsomy (heterozygous) indicates a meiosis I error. IsodIsomy (homozygous) indicates a meiosis II error or postzygotic chromosomal duplication of one of a pair of chromosomes, and loss of the other of the original pair. Uniparental is euploid (correct number of chromosomes). Most occurrences of uniparental disomy (UPD)  normal phenotype. Consider isodisomy in an individual manifesting a recessive disorder when only one parent is a carrier. Examples: Prader-Willi and Angelman syndromes.


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First_Aid_Step1. If p and q represent the frequencies of alleles A and a, respectively, in a population, then p + q = 1: p2 = frequency of homozygosity for allele A q2 = frequency of homozygosity for allele a 2pq = frequency of heterozygosity (carrier frequency, if an autosomal recessive disease) Therefore, the sum of the frequencies of these genotypes is p2 + 2pq + q2 = 1. The frequency of an X-linked recessive disease in males = q and in females = q2. Hardy-Weinberg law assumptions include: No mutation occurring at the locus Natural selection is not occurring If a population is in Hardy-Weinberg equilibrium, then the values of p and q remain constant from generation to generation. Disorders of imprinting Imprinting—one gene copy is silenced by methylation, and only the other copy is expressed  parent-of-origin effects. Modes of inheritance Autosomal dominant Often due to defects in structural genes. Many generations, both males and females are affected. AaaaAaAaaaaa


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First_Aid_Step1. Modes of inheritance Autosomal dominant Often due to defects in structural genes. Many generations, both males and females are affected. AaaaAaAaaaaa Often pleiotropic (multiple apparently unrelated effects) and variably expressive (different between individuals). Family history crucial to diagnosis. With one affected (heterozygous) parent, on average, 1/2 of children affected. Autosomal recessive With 2 carrier (heterozygous) parents, on average: Often due to enzyme deficiencies. Usually seen ¼ of children will be affected (homozygous), in only 1 generation. Commonly more severe 1/2 of children will be carriers, and ¼ of than dominant disorders; patients often present children will be neither affected nor carriers. in childhood. Aa  risk in consanguineous families. Unaffected individual with affected sibling has 2/3 probability of being a carrier.


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First_Aid_Step1. Aa  risk in consanguineous families. Unaffected individual with affected sibling has 2/3 probability of being a carrier. X-linked recessive Sons of heterozygous mothers have a 50% Commonly more severe in males. Females chance of being affected. No male-to-male usually must be homozygous to be affected. transmission. Skips generations. transmit to all daughters but no sons. XXXXXXXYXYXYXXXXXXXYXYXY X-linked dominant Transmitted through both parents. Mothers Examples: fragile X syndrome, Alport syndrome, transmit to 50% of daughters and sons; fathers hypophosphatemic rickets (also called X-linked hypophosphatemia)—phosphate wasting at proximal tubule • rickets-like presentation. Mitochondrial Transmitted only through the mother. All inheritance offspring of affected females may show signs of disease. Variable expression in a population or even within a family due to heteroplasmy.


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First_Aid_Step1. Mitochondrial myopathies—rare disorders; often present with myopathy, lactic acidosis, and CNS disease, eg, MELAS syndrome (mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes). 2° to failure in oxidative phosphorylation. Muscle biopsy often shows “ragged red fibers” (due to accumulation of diseased mitochondria in the subsarcolemma of the muscle fiber). Leber hereditary optic neuropathy—cell death in optic nerve neurons  subacute bilateral vision loss in teens/young adults, 90% males. Usually permanent. = a˜ected female.


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First_Aid_Step1. Leber hereditary optic neuropathy—cell death in optic nerve neurons  subacute bilateral vision loss in teens/young adults, 90% males. Usually permanent. = a˜ected female. Autosomal dominant Achondroplasia, autosomal dominant polycystic kidney disease, familial adenomatous polyposis, diseases familial hypercholesterolemia, hereditary hemorrhagic telangiectasia (Osler-Weber-Rendu syndrome), hereditary spherocytosis, Huntington disease, Li-Fraumeni syndrome, Marfan syndrome, multiple endocrine neoplasias, myotonic muscular dystrophy, neurofibromatosis type 1 (von Recklinghausen disease), neurofibromatosis type 2, tuberous sclerosis, von Hippel-Lindau disease.


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First_Aid_Step1. Autosomal recessive Oculocutaneous albinism, autosomal recessive polycystic kidney disease (ARPKD), cystic diseases fibrosis, Friedreich ataxia, glycogen storage diseases, hemochromatosis, Kartagener syndrome, mucopolysaccharidoses (except Hunter syndrome), phenylketonuria, sickle cell anemia, sphingolipidoses (except Fabry disease), thalassemias, Wilson disease. GENETICS Autosomal recessive; defect in CFTR gene on chromosome 7; commonly a deletion of Phe508. Most common lethal genetic disease in Caucasian population.


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First_Aid_Step1. GENETICS Autosomal recessive; defect in CFTR gene on chromosome 7; commonly a deletion of Phe508. Most common lethal genetic disease in Caucasian population. PATHOPHYSIOlOGY CFTR encodes an ATP-gated Cl− channel that secretes Cl− in lungs and GI tract, and reabsorbs Cl− in sweat glands. Most common mutation  misfolded protein  protein retained in RER and not transported to cell membrane, causing  Cl− (and H2O) secretion;  intracellular Cl− results in compensatory • Na+ reabsorption via epithelial Na+ channels (ENaC)  H2O reabsorption  abnormally thick mucus secreted into lungs and GI tract.  Na+ reabsorption also causes more negative transepithelial potential difference.


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First_Aid_Step1. DIAGNOSIS  Cl− concentration in pilocarpine-induced sweat test is diagnostic. Can present with contraction alkalosis and hypokalemia (ECF effects analogous to a patient taking a loop diuretic) because of ECF H2O/Na+ losses via sweating and concomitant renal K+/H+ wasting. • immunoreactive trypsinogen (newborn screening). COMPlICATIONS Recurrent pulmonary infections (eg, S aureus [infancy and early childhood], P aeruginosa [adulthood], allergic bronchopulmonary aspergillosis [ABPA]), chronic bronchitis and bronchiectasis  reticulonodular pattern on CXR, opacification of sinuses. Pancreatic insufficiency, malabsorption with steatorrhea, fat-soluble vitamin deficiencies (A, D, E, K), biliary cirrhosis, liver disease. Meconium ileus in newborns. Infertility in men (absence of vas deferens, spermatogenesis may be unaffected) and subfertility in women (amenorrhea, abnormally thick cervical mucus). Nasal polyps, clubbing of nails.


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First_Aid_Step1. TREATMENT Multifactorial: chest physiotherapy, albuterol, aerosolized dornase alfa (DNase), and hypertonic saline facilitate mucus clearance. Azithromycin used as anti-inflammatory agent. Ibuprofen slows disease progression. Pancreatic enzyme replacement therapy for pancreatic insufficiency. In patients with Phe508 deletion: combination of lumacaftor (corrects misfolded proteins and improves their transport to cell surface) and ivacaftor (opens Cl– channels • improved chloride transport). Ornithine transcarbamylase deficiency, Fabry disease, Wiskott-Aldrich syndrome, Ocular albinism, G6PD deficiency, Hunter syndrome, Bruton agammaglobulinemia, Hemophilia A and B, Lesch-Nyhan syndrome, Duchenne (and Becker) muscular dystrophy. X-inactivation (lyonization)—one copy of female X chromosome forms a transcriptionally inactive Barr body. Female carriers variably affected depending on the pattern of inactivation of the X chromosome carrying the mutant vs normal gene.


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First_Aid_Step1. X-linked disorder typically due to frameshift deletions or nonsense mutations  truncated or absent dystrophin protein • progressive myofiber damage. Weakness begins in pelvic girdle muscles and progresses superiorly. Pseudohypertrophy of calf muscles due to fibrofatty replacement of muscle A . Waddling gait. Onset before 5 years of age. Dilated cardiomyopathy is common cause of death. Gowers sign—patient uses upper extremities to help stand up. Classically seen in Duchenne muscular dystrophy, but also seen in other muscular dystrophies and inflammatory myopathies (eg, polymyositis). Females with Turner syndrome (45,XO) are more likely to have an X-linked recessive disorder. Duchenne = deleted dystrophin.


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First_Aid_Step1. Females with Turner syndrome (45,XO) are more likely to have an X-linked recessive disorder. Duchenne = deleted dystrophin. Dystrophin gene (DMD) is the largest protein-coding human gene  chance of spontaneous mutation. Dystrophin helps anchor muscle fibers, primarily in skeletal and cardiac muscle. It connects the intracellular cytoskeleton (actin) to the transmembrane proteins αand β-dystroglycan, which are connected to the extracellular matrix (ECM). Loss of dystrophin • myonecrosis.  CK and aldolase; genetic testing confirms diagnosis. Rett syndrome Sporadic disorder seen almost exclusively in girls (affected males die in utero or shortly after birth). Most cases are caused by de novo mutation of MECP2 on X chromosome. Symptoms of Rett syndrome usually appear between ages 1–4 and are characterized by regression (Retturn) in motor, verbal, and cognitive abilities; ataxia; seizures; growth failure; and stereotyped hand-wringing.


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First_Aid_Step1. Myotonic dystrophy (CTG)n AD Cataracts, Toupee (early balding in men), Gonadal atrophy in men, reduced fertility in women Fragile X syndrome (CGG)n XD Chin (protruding), Giant Gonads Findings: intellectual disability, flat facies, prominent epicanthal folds, single palmar crease, incurved 5th finger, gap between 1st 2 toes, duodenal atresia, Hirschsprung disease, congenital heart disease (eg, ASD), Brushfield spots. Associated with early-onset Alzheimer disease (chromosome 21 codes for amyloid precursor protein),  risk of AML/ALL. 95% of cases due to meiotic nondisjunction ( with advanced maternal age; from 1:1500 in women < 20 to 1:25 in women > 45 years old). 4% of cases due to unbalanced Robertsonian translocation, most typically between chromosomes 14 and 21. Only 1% of cases are due to postfertilization mitotic error. Incidence 1:700. Drinking age (21). Most common viable chromosomal disorder and most common cause of genetic intellectual disability.


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First_Aid_Step1. Incidence 1:700. Drinking age (21). Most common viable chromosomal disorder and most common cause of genetic intellectual disability. translucency and hypoplastic nasal bone. Markers for Down syndrome are HI up: hCG, • inhibin. The 5 A’s of Down syndrome: Findings: severe intellectual disability, rocker-bottom feet, microphthalmia, microcephaly, cleft liP/Palate, holoProsencephaly, Polydactyly, cutis aPlasia, congenital heart (Pump) disease, Polycystic kidney disease, omphalocele. Death usually occurs by age 1. Incidence 1:15,000. Puberty (13). Defect in fusion of prechordal mesoderm  midline defects.


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First_Aid_Step1. Incidence 1:15,000. Puberty (13). Defect in fusion of prechordal mesoderm  midline defects. Genetic disorders by chromosome 3 von Hippel-Lindau disease, renal cell carcinoma 4 ADPKD (PKD2), achondroplasia, Huntington disease 5 Cri-du-chat syndrome, familial adenomatous polyposis 7 Williams syndrome, cystic fibrosis 9 Friedreich ataxia, tuberous sclerosis (TSC1) 11 Wilms tumor, β-globin gene defects (eg, sickle cell disease, β-thalassemia), MEN1 13 Patau syndrome, Wilson disease, retinoblastoma (RB1), BRCA2 15 Prader-Willi syndrome, Angelman syndrome, Marfan syndrome 16 ADPKD (PKD1), α-globin gene defects (eg, α-thalassemia), tuberous sclerosis (TSC2) 17 Neurofibromatosis type 1, BRCA1, TP53 22 Neurofibromatosis type 2, DiGeorge syndrome (22q11) X Fragile X syndrome, X-linked agammaglobulinemia, Klinefelter syndrome (XXY)


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First_Aid_Step1. X Fragile X syndrome, X-linked agammaglobulinemia, Klinefelter syndrome (XXY) Chromosomal translocation that commonly involves chromosome pairs 21, 22, 13, 14, and 15. One of the most common types of translocation. Occurs when the long arms of 2 acrocentric chromosomes (chromosomes with centromeres near their ends) fuse at the centromere and the 2 short arms are lost. Balanced translocations normally do not cause any abnormal phenotype. Unbalanced translocations can result in miscarriage, stillbirth, and chromosomal imbalance (eg, Down syndrome, Patau syndrome). Cri-du-chat syndrome Cri du chat = cry of the cat. Congenital deletion on short arm of chromosome 5 (46,XX or XY, 5p−). Findings: microcephaly, moderate to severe intellectual disability, high-pitched crying/meowing, epicanthal folds, cardiac abnormalities (VSD).


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First_Aid_Step1. Williams syndrome Congenital microdeletion of long arm of chromosome 7 (deleted region includes elastin gene). Findings: distinctive “elfin” facies A , intellectual disability, hypercalcemia, well-developed verbal skills, extreme friendliness with strangers, cardiovascular problems (eg, supravalvular aortic stenosis, renal artery stenosis). Think Will Ferrell in Elf. Vitamins: water soluble B1 (thiamine: TPP) B2 (riboflavin: FAD, FMN) B3 (niacin: NAD+) B5 (pantothenic acid: CoA) B6 (pyridoxine: PLP) B7 (biotin) B9 (folate) B12 (cobalamin) C (ascorbic acid) All wash out easily from body except B12 and B9 (folate). B12 stored in liver for ~ 3–4 years. B9 stored in liver for ~ 3–4 months. B-complex deficiencies often result in dermatitis, glossitis, and diarrhea. Can be coenzymes (eg, ascorbic acid) or precursors to coenzymes (eg, FAD, NAD+). Vitamin A Includes retinal, retinol, retinoic acid.


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First_Aid_Step1. Can be coenzymes (eg, ascorbic acid) or precursors to coenzymes (eg, FAD, NAD+). Vitamin A Includes retinal, retinol, retinoic acid. DEFICIENCY Night blindness (nyctalopia); dry, scaly skin (xerosis cutis); corneal squamous metaplasia • Bitot spots (keratin debris; foamy appearance on conjunctiva A ); corneal degeneration (keratomalacia); immunosuppression. EXCESS Acute toxicity—nausea, vomiting, vertigo, and Isotretinoin is teratogenic. blurred vision. Chronic toxicity—alopecia, dry skin (eg, scaliness), hepatic toxicity and enlargement, arthralgias, and idiopathic intracranial hypertension. Teratogenic (cleft palate, cardiac abnormalities), therefore a ⊝ pregnancy test and two forms of contraception are required before isotretinoin (vitamin A derivative) is prescribed. Vitamin B1 Also called thiamine.


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First_Aid_Step1. Vitamin B1 Also called thiamine. DEFICIENCY Impaired glucose breakdown  ATP depletion worsened by glucose infusion; highly aerobic tissues (eg, brain, heart) are affected first. In alcoholic or malnourished patients, give thiamine before dextrose to  risk of precipitating Wernicke encephalopathy. Diagnosis made by  in RBC transketolase activity following vitamin B1 administration. chronic alcohol consumption; presents with confabulation, personality changes, memory loss (permanent). Wernicke-Korsakoff syndrome—damage to medial dorsal nucleus of thalamus, mammillary bodies. Presentation is combination of Wernicke encephalopathy and Korsakoff syndrome. Dry beriberi—polyneuropathy, symmetric muscle wasting. Wet beriberi—high-output cardiac failure (dilated cardiomyopathy), edema. DEFICIENCY Cheilosis (inflammation of lips, scaling and The 2 C’s of B2. fissures at the corners of the mouth), Corneal vascularization. Vitamin B3 Also called niacin, nicotinic acid.


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First_Aid_Step1. DEFICIENCY Cheilosis (inflammation of lips, scaling and The 2 C’s of B2. fissures at the corners of the mouth), Corneal vascularization. Vitamin B3 Also called niacin, nicotinic acid. FUNCTION Constituent of NAD+, NADP+ (used in redox NAD derived from Niacin (B3 ≈ 3 ATP). reactions). Derived from tryptophan. Synthesis requires vitamins B2 and B6. Used to treat dyslipidemia; lowers levels of VLDL and raises levels of HDL. DEFICIENCY Glossitis. Severe deficiency leads to pellagra, which can also be caused by Hartnup disease, malignant carcinoid syndrome (• tryptophan metabolism), and isoniazid ( vitamin B6). Symptoms of pellagra: Diarrhea, Dementia (also hallucinations), Dermatitis (C3/C4 dermatome circumferential “broad collar” rash [Casal necklace], hyperpigmentation of sun-exposed limbs A ). The 3 D’s of B3.


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First_Aid_Step1. A ). The 3 D’s of B3. Hartnup disease—autosomal recessive. Deficiency of neutral amino acid (eg, tryptophan) transporters in proximal renal tubular cells and on enterocytes • neutral aminoaciduria and  absorption from the gut  tryptophan for conversion to niacin  pellagra-like symptoms. Treat with high- protein diet and nicotinic acid. Deficiency of vitamin B3 • pellagra. EXCESS Facial flushing (induced by prostaglandin, not Excess of vitamin B3 • podagra. histamine; can avoid by taking aspirin with niacin), hyperglycemia, hyperuricemia. Vitamin B5 Also called pantothenic acid. FUNCTION Essential component of coenzyme A (CoA, B5 is “pento”thenic acid. a cofactor for acyl transfers) and fatty acid synthase. DEFICIENCY Dermatitis, enteritis, alopecia, adrenal insufficiency. Vitamin B6 Also called pyridoxine.


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First_Aid_Step1. DEFICIENCY Dermatitis, enteritis, alopecia, adrenal insufficiency. Vitamin B6 Also called pyridoxine. FUNCTION Converted to pyridoxal phosphate (PLP), a cofactor used in transamination (eg, ALT and AST), decarboxylation reactions, glycogen phosphorylase. Synthesis of glutathione, cystathionine, heme, niacin, histamine, and neurotransmitters including serotonin, epinephrine, norepinephrine (NE), dopamine, and GABA. DEFICIENCY Convulsions, hyperirritability, peripheral neuropathy (deficiency inducible by isoniazid and oral contraceptives), sideroblastic anemia (due to impaired hemoglobin synthesis and iron excess). Vitamin B7 Also called biotin. a 1-carbon group): Pyruvate carboxylase: pyruvate (3C) • oxaloacetate (4C) Acetyl-CoA carboxylase: acetyl-CoA (2C) • malonyl-CoA (3C) Propionyl-CoA carboxylase: propionyl-CoA (3C)  methylmalonyl-CoA (4C)


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First_Aid_Step1. Pyruvate carboxylase: pyruvate (3C) • oxaloacetate (4C) Acetyl-CoA carboxylase: acetyl-CoA (2C) • malonyl-CoA (3C) Propionyl-CoA carboxylase: propionyl-CoA (3C)  methylmalonyl-CoA (4C) DEFICIENCY Relatively rare. Dermatitis, enteritis, alopecia. “Avidin in egg whites avidly binds biotin.” Caused by long-term antibiotic use or excessive ingestion of raw egg whites. DEFICIENCY Macrocytic, megaloblastic anemia; hypersegmented PMNs; paresthesias and subacute combined degeneration (degeneration of dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts) due to abnormal myelin. Associated with  serum homocysteine and methylmalonic acid levels, along with 2° folate deficiency. Prolonged deficiency  irreversible nerve damage. Vitamin C Also called ascorbic acid.


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First_Aid_Step1. Vitamin C Also called ascorbic acid. (eg, sprue, enteritis, Diphyllobothrium latum, achlorhydria, bacterial overgrowth, alcohol excess), lack of intrinsic factor (eg, pernicious anemia, gastric bypass surgery), absence of terminal ileum (surgical resection, eg, for Crohn disease), certain drugs (eg, metformin), or insufficient intake (eg, veganism). Anti-intrinsic factor antibodies diagnostic for pernicious anemia. Folate supplementation can mask the hematologic symptoms of B12 deficiency, but not the neurologic symptoms. Fatty acids with odd number of carbons, branched-chain amino acids CH3 to anabolic pathways Methylmalonyl-CoA EXCESS Nausea, vomiting, diarrhea, fatigue, calcium oxalate nephrolithiasis. Can  iron toxicity in predisposed individuals by increasing dietary iron absorption (ie, can worsen hereditary hemochromatosis or transfusion-related iron overload).


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First_Aid_Step1. REGUlATION  PTH, • Ca2+,  PO43– • 1,25-(OH)2D3 production. 1,25-(OH)2D3 feedback inhibits its own production.  PTH • Ca2+ reabsorption and  PO43– reabsorption in the kidney. DEFICIENCY Rickets in children (deformity, such as genu varum “bowlegs” A ), osteomalacia in adults (bone pain and muscle weakness), hypocalcemic tetany. Caused by malabsorption,  sun exposure, poor diet, chronic kidney disease (CKD), advanced liver disease. Give oral vitamin D to breastfed infants. Deficiency is exacerbated by pigmented skin, premature birth. EXCESS Hypercalcemia, hypercalciuria, loss of appetite, stupor. Seen in granulomatous diseases ( activation of vitamin D by epithelioid macrophages). Vitamin E Includes tocopherol, tocotrienol. FUNCTION Antioxidant (protects RBCs and membranes from free radical damage). EXCESS Risk of enterocolitis in infants. High-dose supplementation may alter metabolism of vitamin K  enhanced anticoagulant effects of warfarin.


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First_Aid_Step1. EXCESS Risk of enterocolitis in infants. High-dose supplementation may alter metabolism of vitamin K  enhanced anticoagulant effects of warfarin. Vitamin K Includes phytomenadione, phylloquinone, phytonadione, menaquinone. FUNCTION Mineral essential for the activity of 100+ enzymes. Important in the formation of zinc fingers (transcription factor motif). DEFICIENCY Delayed wound healing, suppressed immunity, male hypogonadism,  adult hair (axillary, facial, pubic), dysgeusia, anosmia. Associated with acrodermatitis enteropathica ( A , defect in intestinal zinc absorption). May predispose to alcoholic cirrhosis. Kwashiorkor Protein malnutrition resulting in skin lesions, edema due to  plasma oncotic pressure, liver malfunction (fatty change due to  apolipoprotein synthesis). Clinical picture is small child with swollen abdomen A . Kwashiorkor results from protein- deficient MEALS: Malnutrition Edema Anemia Liver (fatty) Skin lesions (eg, hyperkeratosis,


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First_Aid_Step1. A . Kwashiorkor results from protein- deficient MEALS: Malnutrition Edema Anemia Liver (fatty) Skin lesions (eg, hyperkeratosis, Marasmus Malnutrition not causing edema. Diet is deficient in calories but no nutrients are entirely absent. Marasmus results in Muscle wasting B . Fomepizole—blocks alcohol DH; antidote For Overdoses of Methanol or Ethylene glycol. • discouraging drinking. NAD+ is the limiting reagent. Alcohol dehydrogenase operates via zero-order kinetics. Ethanol metabolism  NADH/ NAD+ ratio in liver, causing: Lactic acidosis— pyruvate conversion to lactate Fasting hypoglycemia— gluconeogenesis due to of OAA to malate Ketoacidosis—diversion of acetyl-CoA into ketogenesis rather than TCA cycle Hepatosteatosis— • conversion of DHAP to glycerol-3-P 4B , which combines with glycerol-3-P to synthesize triglycerides  NADH/NAD+ ratio inhibits TCA cycle  acetyl-CoA used in ketogenesis (• ketoacidosis), lipogenesis (• hepatosteatosis).


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First_Aid_Step1. Mitochondria Fatty acid oxidation (β-oxidation), acetyl-CoA production, TCA cycle, oxidative phosphorylation, ketogenesis. Cytoplasm Glycolysis, HMP shunt, and synthesis of cholesterol (SER), proteins (ribosomes, RER), fatty acids, and nucleotides. Both Heme synthesis, Urea cycle, Gluconeogenesis. HUGs take two (both). Enzyme terminology An enzyme’s name often describes its function. For example, glucokinase is an enzyme that catalyzes the phosphorylation of glucose using a molecule of ATP. The following are commonly used enzyme descriptors. Kinase Catalyzes transfer of a phosphate group from a high-energy molecule (usually ATP) to a substrate (eg, phosphofructokinase). Phosphorylase Adds inorganic phosphate onto substrate without using ATP (eg, glycogen phosphorylase). Phosphatase Removes phosphate group from substrate (eg, fructose-1,6-bisphosphatase). Dehydrogenase Catalyzes oxidation-reduction reactions (eg, pyruvate dehydrogenase).


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First_Aid_Step1. Phosphatase Removes phosphate group from substrate (eg, fructose-1,6-bisphosphatase). Dehydrogenase Catalyzes oxidation-reduction reactions (eg, pyruvate dehydrogenase). Hydroxylase Adds hydroxyl group (−OH) onto substrate (eg, tyrosine hydroxylase). Carboxylase Transfers CO2 groups with the help of biotin (eg, pyruvate carboxylase). Mutase Relocates a functional group within a molecule (eg, vitamin B12–dependent methylmalonyl-CoA mutase). Synthase/synthetase Joins two molecules together using a source of energy (eg, ATP, acetyl-CoA, nucleotide sugar). Rate-determining enzymes of metabolic processes Summary of pathways


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First_Aid_Step1. T B T T B B Glycogen UDP-glucose Glucose-1-phosphate Glucose Glucose-6-phosphate 6-phosphogluconolactone Fructose-6-phosphate Fructose-1,6-bisphosphate Glyceraldehyde-3-P DHAP 1,3-bisphosphoglycerate 3-phosphoglycerate 2-phosphoglycerate Phosphoenolpyruvate (PEP) Pyruvate Alanine Acetyl-CoA Glyceraldehyde Ribulose-5-phosphate Fructose-1-phosphate Fructose NH3 + CO2 Carbamoyl phosphate Citrulline Aspartate Argininosuccinate Urea cycle Ornithine Urea H2O Arginine Fumarate Oxaloacetate Malate TCA cycle Succinate Citrate Isocitrate ˜-ketoglutarate Succinyl-CoA Methylmalonyl-CoA Propionyl-CoA Odd-chain fatty acids, isoleucine, valine, methionine, threonine Acetoacetate ˜-hydroxybutyrate Mevalonate Galactose Galactose-1-phosphate HMP shunt Fructose metabolism Lipid metabolism Galactose metabolism Gluconeogenesis Ketogenesis Glycolysis Protein metabolism Glycogenesis / glycogenolysis Lactate Acetoacetyl-CoA HMG-CoA Malonyl-CoA Triglycerides Glycerol Cholesterol B12 Irreversible, important


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First_Aid_Step1. Gluconeogenesis Ketogenesis Glycolysis Protein metabolism Glycogenesis / glycogenolysis Lactate Acetoacetyl-CoA HMG-CoA Malonyl-CoA Triglycerides Glycerol Cholesterol B12 Irreversible, important point of regulation Requires thiamine cofactor (TPP)Requires biotin cofactor B T Fatty acids #Hexokinase/glucokinase Glucose-6-phosphatase (von Gierke disease) Glucose-6-phosphate dehydrogenase Transketolase Pyruvate kinase Pyruvate dehydrogenase HMG-CoA reductase Pyruvate carboxylase PEP carboxykinase Citrate synthase Triose phosphate isomerase Phosphofructokinase-1 Fructose-1,6-bisphosphatase Fructokinase (essential fructosuria) Aldolase B (fructose intolerance) Aldolase B (liver), A (muscle) Isocitrate dehydrogenase ˜-ketoglutarate dehydrogenase Ornithine transcarbamylase Propionyl-CoA carboxylase Carbamoyl phosphate synthetase I Galactokinase (mild galactosemia) Galactose-1-phosphate uridyltransferase (severe galactosemia)


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First_Aid_Step1. NADH, NADPH, FADH2 Electrons CoA, lipoamide Acyl groups Phosphorylation of glucose to yield glucose-6-phosphate is catalyzed by glucokinase in the liver and hexokinase in other tissues. Hexokinase sequesters glucose in tissues, where it is used even when glucose concentrations are low. At high glucose concentrations, glucokinase helps to store glucose in liver. Glucose-6-P Glucose-6-P ⊝ hexokinase. Fructose-6-P ⊝ glucokinase. Fructose-6-P Fructose-1,6-BP AMP ⊕, fructose-2,6-bisphosphate ⊕. ATP ⊝, citrate ⊝. Regulation by fructose-2,6bisphosphate Fructose bisphosphatase-2 (FBPase-2) and phosphofructokinase-2 (PFK-2) are the same bifunctional enzyme whose function is reversed by phosphorylation by protein kinase A. Fructose-1,6-BP Fructose-2,6-BP Fasting state:  glucagon  cAMP  protein FaBian the Peasant (FBP) has to work hard kinase A  FBPase-2,  PFK-2, less when starving. glycolysis, more gluconeogenesis.


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First_Aid_Step1. Fructose-2,6-BP Fasting state:  glucagon  cAMP  protein FaBian the Peasant (FBP) has to work hard kinase A  FBPase-2,  PFK-2, less when starving. glycolysis, more gluconeogenesis. Fed state:  insulin  cAMP  protein Prince FredericK (PFK) works only when fed. kinase A  FBPase-2,  PFK-2, more glycolysis, less gluconeogenesis. Mitochondrial enzyme complex linking glycolysis and TCA cycle. Differentially regulated in fed (active)/fasting (inactive) states. Reaction: pyruvate + NAD+ + CoA  acetyl-CoA + CO2 + NADH. Contains 3 enzymes requiring 5 cofactors: 1. 2. 3. CoA (B5, pantothenic acid) 4. FAD (B2, riboflavin) 5. NAD+ (B3, niacin) Activated by: • NAD+/NADH ratio,  ADP • Ca2+ The complex is similar to the α-ketoglutarate dehydrogenase complex (same cofactors, similar substrate and action), which converts α-ketoglutarate  succinyl-CoA (TCA cycle). The Lovely Coenzymes For Nerds.


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First_Aid_Step1. The Lovely Coenzymes For Nerds. Arsenic inhibits lipoic acid. Arsenic poisoning clinical findings: imagine a vampire (pigmentary skin changes, skin cancer), vomiting and having diarrhea, running away from a cutie (QT prolongation) with garlic breath. FINDINGS Neurologic defects, lactic acidosis,  serum alanine starting in infancy. TREATMENT  intake of ketogenic nutrients (eg, high fat content or • lysine and leucine). Functions of different pyruvate metabolic pathways (and their associated cofactors): Alanine aminotransferase (B6): alanine carries amino groups to the liver from muscle Pyruvate carboxylase (biotin): oxaloacetate can replenish TCA cycle or be used in gluconeogenesis Pyruvate dehydrogenase (B1, B2, B3, B5, lipoic acid): transition from glycolysis to the TCA cycle Lactic acid dehydrogenase (B3): end of anaerobic glycolysis (major pathway in RBCs, WBCs, kidney medulla, lens, testes, and cornea) Also called Krebs cycle. Pyruvate  acetyl-CoA produces 1 NADH, 1 CO2.


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First_Aid_Step1. Also called Krebs cycle. Pyruvate  acetyl-CoA produces 1 NADH, 1 CO2. The TCA cycle produces 3 NADH, 1 FADH2, 2 CO2, 1 GTP per acetyl-CoA = 10 ATP/ acetyl-CoA (2× everything per glucose). TCA cycle reactions occur in the mitochondria. α-ketoglutarate dehydrogenase complex requires the same cofactors as the pyruvate dehydrogenase complex (vitamins B1, B2, B3, B5, lipoic acid). Citrate Is Krebs’ Starting Substrate For Making Oxaloacetate. Electron transport NADH electrons from glycolysis enter mitochondria via the malate-aspartate or glycerol-3chain and oxidative phosphate shuttle. FADH2 electrons are transferred to complex II (at a lower energy level than phosphorylation NADH). The passage of electrons results in the formation of a proton gradient that, coupled to oxidative phosphorylation, drives the production of ATP.


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First_Aid_Step1. Complex I Complex II Complex III Complex IV Complex V Rotenone Antimycin A Azide, Oligomycin (succinate dehydrogenase) Cyanide, CO2 NADH NAD+ FADH2 FAD 1/2O2 + 2H+ H2O H+H+ H+ H+ CoQ Cyto-chrome c space2,4-Dinitrophenol Aspirin overdose 1 NADH  2.5 ATP; 1 FADH2  1.5 ATP. Gluconeogenesis, irreversible enzymes Pathway Produces Fresh Glucose. Pyruvate carboxylase In mitochondria. Pyruvate  oxaloacetate. Requires biotin, ATP. Activated by acetyl-CoA. Phosphoenolpyruvate In cytosol. Oxaloacetate Requires GTP. carboxykinase • phosphoenolpyruvate. Fructose-1,6-In cytosol. Fructose-1,6-bisphosphate Citrate ⊕, AMP ⊝, fructose 2,6-bisphosphate ⊝. bisphosphatase  fructose-6-phosphate. Glucose-6-In ER. Glucose-6-phosphate  glucose. phosphatase


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First_Aid_Step1. Fructose-1,6-In cytosol. Fructose-1,6-bisphosphate Citrate ⊕, AMP ⊝, fructose 2,6-bisphosphate ⊝. bisphosphatase  fructose-6-phosphate. Glucose-6-In ER. Glucose-6-phosphate  glucose. phosphatase Occurs primarily in liver; serves to maintain euglycemia during fasting. Enzymes also found in kidney, intestinal epithelium. Deficiency of the key gluconeogenic enzymes causes hypoglycemia. (Muscle cannot participate in gluconeogenesis because it lacks glucose-6-phosphatase). Odd-chain fatty acids yield 1 propionyl-CoA during metabolism, which can enter the TCA cycle (as succinyl-CoA), undergo gluconeogenesis, and serve as a glucose source. Even-chain fatty acids cannot produce new glucose, since they yield only acetyl-CoA equivalents.


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First_Aid_Step1. Also called HMP shunt. Provides a source of NADPH from abundantly available glucose-6-P (NADPH is required for reductive reactions, eg, glutathione reduction inside RBCs, fatty acid and cholesterol biosynthesis). Additionally, this pathway yields ribose for nucleotide synthesis. Two distinct phases (oxidative and nonoxidative), both of which occur in the cytoplasm. No ATP is used or produced. Sites: lactating mammary glands, liver, adrenal cortex (sites of fatty acid or steroid synthesis), RBCs. Transketolase, B˜ Fructose Nucleotide 1,6-bisphosphate synthesis


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First_Aid_Step1. Sites: lactating mammary glands, liver, adrenal cortex (sites of fatty acid or steroid synthesis), RBCs. Transketolase, B˜ Fructose Nucleotide 1,6-bisphosphate synthesis NADPH is necessary to keep glutathione reduced, which in turn detoxifies free radicals and peroxides.  NADPH in RBCs leads to hemolytic anemia due to poor RBC defense against oxidizing agents (eg, fava beans, sulfonamides, nitrofurantoin, primaquine/ chloroquine, antituberculosis drugs). Infection (most common cause) can also precipitate hemolysis; inflammatory response produces free radicals that diffuse into RBCs, causing oxidative damage. X-linked recessive disorder; most common human enzyme deficiency; more prevalent among African Americans.  malarial resistance. Heinz bodies—denatured globin chains precipitate within RBCs due to oxidative stress. Bite cells—result from the phagocytic removal of Heinz bodies by splenic macrophages. Think, “Bite into some Heinz ketchup.” Disorders of fructose metabolism


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First_Aid_Step1. Bite cells—result from the phagocytic removal of Heinz bodies by splenic macrophages. Think, “Bite into some Heinz ketchup.” Disorders of fructose metabolism Essential fructosuria Involves a defect in fructokinase. Autosomal recessive. A benign, asymptomatic condition (fructokinase deficiency is kinder), since fructose is not trapped in cells. Hexokinase becomes 1° pathway for converting fructose to fructose-6-phosphate. Symptoms: fructose appears in blood and urine. Disorders of fructose metabolism cause milder symptoms than analogous disorders of galactose metabolism.


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First_Aid_Step1. Hereditary deficiency of aldolase B. Autosomal recessive. Fructose-1-phosphate accumulates, causing a  in available phosphate, which results in inhibition of glycogenolysis and gluconeogenesis. Symptoms present following consumption of fruit, juice, or honey. Urine dipstick will be ⊝ (tests for glucose only); reducing sugar can be detected in the urine (nonspecific test for inborn errors of carbohydrate metabolism). Symptoms: hypoglycemia, jaundice, cirrhosis, vomiting. Treatment:  intake of fructose, sucrose (glucose + fructose), and sorbitol (metabolized to fructose). Disorders of galactose metabolism Hereditary deficiency of galactokinase. Galactitol accumulates if galactose is present in diet. Fructose is to Aldolase B as Galactose is to UridylTransferase (FAB GUT). The more serious defects lead to PO43− depletion.


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First_Aid_Step1. Fructose is to Aldolase B as Galactose is to UridylTransferase (FAB GUT). The more serious defects lead to PO43− depletion. Sorbitol An alternative method of trapping glucose in the cell is to convert it to its alcohol counterpart, sorbitol, via aldose reductase. Some tissues then convert sorbitol to fructose using sorbitol dehydrogenase; tissues with an insufficient amount/activity of this enzyme are at risk of intracellular sorbitol accumulation, causing osmotic damage (eg, cataracts, retinopathy, and peripheral neuropathy seen with chronic hyperglycemia in diabetes). High blood levels of galactose also result in conversion to the osmotically active galactitol via aldose reductase. Liver, Ovaries, and Seminal vesicles have both enzymes (they LOSe sorbitol). Lens has primarily aldose reductase. Retina, Kidneys, and Schwann cells have only aldose reductase (LuRKS).


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First_Aid_Step1. Lens has primarily aldose reductase. Retina, Kidneys, and Schwann cells have only aldose reductase (LuRKS). Lactase deficiency Insufficient lactase enzyme  dietary lactose intolerance. Lactase functions on the intestinal brush border to digest lactose (in milk and milk products) into glucose and galactose. Primary: age-dependent decline after childhood (absence of lactase-persistent allele), common in people of Asian, African, or Native American descent. Secondary: loss of intestinal brush border due to gastroenteritis (eg, rotavirus), autoimmune disease. Congenital lactase deficiency: rare, due to defective gene. Stool demonstrates  pH and breath shows  hydrogen content with lactose hydrogen breath test. Intestinal biopsy reveals normal mucosa in patients with hereditary lactose intolerance. FINDINGS Bloating, cramps, flatulence, osmotic diarrhea. TREATMENT Avoid dairy products or add lactase pills to diet; lactose-free milk.


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First_Aid_Step1. FINDINGS Bloating, cramps, flatulence, osmotic diarrhea. TREATMENT Avoid dairy products or add lactase pills to diet; lactose-free milk. Amino acids Only l-amino acids are found in proteins. Essential PVT TIM HaLL: Phenylalanine, Valine, Tryptophan, Threonine, Isoleucine, Methionine, Histidine, Leucine, Lysine. Glucogenic: Methionine, histidine, valine. We met his valentine, she is so sweet (glucogenic). Glucogenic/ketogenic: Isoleucine, phenylalanine, threonine, tryptophan. Ketogenic: Leucine, Lysine. The onLy pureLy ketogenic amino acids. Acidic Aspartic acid, glutamic acid. Negatively charged at body pH. Basic Arginine, histidine, lysine. Arginine is most basic. Histidine has no charge at body pH. Arginine and histidine are required during periods of growth. Arginine and lysine are  in histones which bind negatively charged DNA. His lys (lies) are basic. Transport of ammonia by alanine


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First_Aid_Step1. Transport of ammonia by alanine Hyperammonemia Can be acquired (eg, liver disease) or hereditary Treatment: limit protein in diet. (eg, urea cycle enzyme deficiencies). May be given to  ammonia levels: Presents with flapping tremor (eg, asterixis), • Lactulose to acidify GI tract and trap NH4+ slurring of speech, somnolence, vomiting, for excretion. cerebral edema, blurring of vision. • Antibiotics (eg, rifaximin, neomycin) to  NH3 changes relative amounts of • ammoniagenic bacteria. α-ketoglutarate, glutamate, GABA, and • Benzoate, phenylacetate, or phenylbutyrate glutamine to favor  glutamine. CNS toxicity react with glycine or glutamine, forming may involve  GABA, • α-ketoglutarate, TCA products that are excreted renally. cycle inhibition, and cerebral edema due to glutamine-induced osmotic shifts. NH NH


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First_Aid_Step1. Most common urea cycle disorder. X-linked recessive (vs other urea cycle enzyme deficiencies, which are autosomal recessive). Interferes with the body’s ability to eliminate ammonia. Often evident in the first few days of life, but may present later. Excess carbamoyl phosphate is converted to orotic acid (part of the pyrimidine synthesis pathway). Findings:  orotic acid in blood and urine,  BUN, symptoms of hyperammonemia. No megaloblastic anemia (vs orotic aciduria). , B6 Tryptophan BH4, B6 Serotonin Due to • phenylalanine hydroxylase or tetrahydrobiopterin (BH4) cofactor (malignant PKU). Tyrosine becomes essential. phenylalanine  phenyl ketones in urine. Findings: intellectual disability, growth retardation, seizures, fair complexion, eczema, musty body odor. Treatment: • phenylalanine and  tyrosine in diet, tetrahydrobiopterin supplementation.


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First_Aid_Step1. Findings: intellectual disability, growth retardation, seizures, fair complexion, eczema, musty body odor. Treatment: • phenylalanine and  tyrosine in diet, tetrahydrobiopterin supplementation. Maternal PKU—lack of proper dietary therapy during pregnancy. Findings in infant: microcephaly, intellectual disability, growth retardation, congenital heart defects. Autosomal recessive. Incidence ≈ 1:10,000. Screening occurs 2–3 days after birth (normal at birth because of maternal enzyme during fetal life). Phenyl ketones—phenylacetate, phenyllactate, and phenylpyruvate. Disorder of aromatic amino acid metabolism  musty body odor. PKU patients must avoid the artificial sweetener aspartame, which contains phenylalanine. Autosomal recessive. Presentation: vomiting, poor feeding, urine smells like maple syrup/burnt sugar. Causes severe CNS defects, intellectual disability, death. I Love Vermont maple syrup from maple trees (with B1ranches).


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First_Aid_Step1. I Love Vermont maple syrup from maple trees (with B1ranches). Blocked degradation of branched amino acids (Isoleucine, Leucine, Valine) due to • branched-chain α-ketoacid dehydrogenase (B1). Causes • α-ketoacids in the blood, especially those of leucine. Treatment: restriction of isoleucine, leucine, valine in diet, and thiamine supplementation. Congenital deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumarate • pigment-forming homogentisic acid builds up in tissue A . Autosomal recessive. Usually benign. Findings: bluish-black connective tissue, ear cartilage, and sclerae (ochronosis); urine turns black on prolonged exposure to air. May have debilitating arthralgias (homogentisic acid toxic to cartilage). Causes (all autosomal recessive): • Cystathionine synthase deficiency (treatment:  methionine, • cysteine,  B6, B12, and folate in diet) •  affinity of cystathionine synthase for pyridoxal phosphate (treatment:  B6 and


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First_Aid_Step1. Methionine synthase (homocysteine methyltransferase) deficiency (treatment: Methylenetetrahydrofolate reductase (MTHFR) deficiency (treatment:  folate in diet) All forms result in excess homocysteine. HOMOCYstinuria: • Homocysteine in urine, Osteoporosis, Marfanoid habitus, Ocular changes (downward and inward lens subluxation), Cardiovascular effects (thrombosis and atherosclerosis • stroke and MI), kYphosis, intellectual disability, fair complexion. In homocystinuria, lens subluxes “down and in” (vs Marfan, “up and fans out”). Hereditary defect of renal PCT and intestinal amino acid transporter that prevents reabsorption of Cystine, Ornithine, Lysine, and Arginine (COLA). Excess cystine in the urine can lead to recurrent precipitation of hexagonal cystine stones A . Treatment: urinary alkalinization (eg, potassium citrate, acetazolamide) and chelating agents (eg, penicillamine)  solubility of cystine stones; good hydration.


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First_Aid_Step1. Treatment: urinary alkalinization (eg, potassium citrate, acetazolamide) and chelating agents (eg, penicillamine)  solubility of cystine stones; good hydration. Autosomal recessive. Common (1:7000). Urinary cyanide-nitroprusside test is diagnostic. Cystine is made of 2 cysteines connected by a disulfide bond. Organic acidemias Most commonly present in infancy with poor feeding, vomiting, hypotonia, high anion gap metabolic acidosis, hepatomegaly, seizures. Organic acid accumulation: Inhibits gluconeogenesis  fasting blood glucose levels, • ketoacidosis  high anion gap metabolic acidosis Glycogen Branches have α-(1,6) bonds; linkages have α-(1,4) bonds. Skeletal muscle Glycogen undergoes glycogenolysis  glucose-1-phosphate  glucose-6-phosphate, which is rapidly metabolized during exercise.


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First_Aid_Step1. Skeletal muscle Glycogen undergoes glycogenolysis  glucose-1-phosphate  glucose-6-phosphate, which is rapidly metabolized during exercise. Hepatocytes Glycogen is stored and undergoes glycogenolysis to maintain blood sugar at appropriate levels. Glycogen phosphorylase liberates glucose-1-phosphate residues off branched glycogen until 4 glucose units remain on a branch. Then 4-α-d-glucanotransferase (debranching enzyme ) moves 3 of the 4 glucose units from the branch to the linkage. Then α-1,6-glucosidase (debranching enzyme ) cleaves off the last residue, liberating glucose. “Limit dextrin” refers to the two to four residues remaining on a branch after glycogen phosphorylase (˜-1,6-glucosidase) ˜-1,4-glucosidase Note: A small amount of glycogen is degraded in lysosomes by α-1,4-glucosidase (acid maltase). has already shortened it. Gaucher disease Most common.


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First_Aid_Step1. Note: A small amount of glycogen is degraded in lysosomes by α-1,4-glucosidase (acid maltase). has already shortened it. Gaucher disease Most common. Hepatosplenomegaly, pancytopenia, osteoporosis, avascular necrosis of femur, bone crises, Gaucher cells C (lipid-laden macrophages resembling crumpled tissue paper). (β-glucosidase); treat with recombinant glucocerebrosidase C hepatosplenomegaly, foam cells (lipid-laden macrophages) D , Niemann-Pick disease Progressive neurodegeneration, “cherry-red” spot on macula A . Sphingomyelinase Sphingomyelin AR D Mucopolysaccharidoses Hurler syndrome Developmental delay, gargoylism, α-l-iduronidase Heparan sulfate, AR airway obstruction, corneal clouding, dermatan sulfate hepatosplenomegaly. Hunter syndrome Mild Hurler + aggressive behavior, no Iduronate-2-sulfatase Heparan sulfate, XR corneal clouding. dermatan sulfate No man picks (Niemann-Pick) his nose with his sphinger (sphingomyelinase).


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First_Aid_Step1. No man picks (Niemann-Pick) his nose with his sphinger (sphingomyelinase). aggressively aim for the X (X-linked recessive).  incidence of Tay-Sachs, Niemann-Pick, some forms of Gaucher disease in Ashkenazi Jews. Sphingolipidoses Tay-Sachs disease A Progressive neurodegeneration, developmental delay, hyperreflexia, hyperacusis, “cherry-red” spot on macula A , lysosomes with onion skin, no hepatosplenomegaly (vs Niemann-Pick). HeXosaminidase A (“TAy-SaX”) GM2 ganglioside AR Fabry disease B Early: triad of episodic peripheral neuropathy, angiokeratomas B , hypohidrosis. Late: progressive renal failure, cardiovascular disease. α-galactosidase A Ceramide trihexoside (globotriaosylce-ramide) XR Metachromatic leukodystrophy Central and peripheral demyelination with ataxia, dementia. Arylsulfatase A Cerebroside sulfate AR (palmitate, a 16C FA)


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First_Aid_Step1. Fatty acid synthesis requires transport of citrate from mitochondria to cytosol. Predominantly occurs in liver, lactating mammary glands, and adipose tissue. Long-chain fatty acid (LCFA) degradation requires carnitine-dependent transport into the mitochondrial matrix. “SYtrate” = SYnthesis. CARnitine = CARnage of fatty acids. Systemic 1° carnitine deficiency—no cellular uptake of carnitine  no transport of LCFAs into mitochondria  toxic accumulation of LCFAs in the cytosol. Causes weakness, hypotonia, hypoketotic hypoglycemia, dilated cardiomyopathy. Medium-chain acyl-CoA dehydrogenase deficiency— ability to break down fatty acids into acetyl-CoA • accumulation of fatty acyl carnitines in the blood with hypoketotic hypoglycemia. Causes vomiting, lethargy, seizures, coma, liver dysfunction, hyperammonemia. Can lead to sudden death in infants or children. Treat by avoiding fasting.


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First_Aid_Step1. Ketone bodies In the liver, fatty acids and amino acids are metabolized to acetoacetate and β-hydroxybutyrate (to be used in muscle and brain). In prolonged starvation and diabetic ketoacidosis, oxaloacetate is depleted for gluconeogenesis. In alcoholism, excess NADH shunts oxaloacetate to malate. All of these processes lead to a buildup of acetyl-CoA, which is shunted into ketone body synthesis. Ketone bodies: acetone, acetoacetate, β-hydroxybutyrate. Breath smells like acetone (fruity odor). Urine test for ketones can detect acetoacetate, but not β-hydroxybutyrate. RBCs cannot utilize ketones; they strictly use glucose. HMG-CoA lyase for ketone production. HMG-CoA reductase for cholesterol synthesis. (liver) Fatty acids, amino acids Acetoacetate AcetoacetateAcetoneATP˜-hydroxybutyrate Expired by lungs TCA cycle (eg, skeletal muscle) ˜-hydroxybutyrate Acetoacetyl-CoA Acetoacetate ˜-hydroxybutyrateAcetyl-CoA HMG-CoA 2 Acetyl-CoA Duration of exercise


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First_Aid_Step1. Duration of exercise Fasting and starvation Priorities are to supply sufficient glucose to the brain and RBCs and to preserve protein. Fed state (after a Glycolysis and aerobic respiration. meal) Fasting (between Hepatic glycogenolysis (major); hepatic meals) gluconeogenesis, adipose release of FFA (minor). Starvation days 1–3 Blood glucose levels maintained by: Adipose release of FFA Muscle and liver, which shift fuel use from glucose to FFA Insulin stimulates storage of lipids, proteins, and glycogen. Glucagon and epinephrine stimulate use of fuel reserves. Glycogen reserves depleted after day 1. RBCs lack mitochondria and therefore cannot use ketones. Weeks of starvation Carbohydrate Protein Fat 1 2 3 4 5 6 7 80 2 10 12 0 Starvation after day 3 Adipose stores (ketone bodies become the main source of energy for the brain). After these are depleted, vital protein degradation accelerates, leading to organ failure and death. Amount of excess stores determines survival time.


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First_Aid_Step1. tissue lactate and alanine, and from CoA (from odd-chain FFA—the only to the liver via Apo E 7 Endocytosis of LDL PCSK9 Degrades LDL receptor  serum LDL. Inhibition  LDL receptor recycling  serum LDL. Transfer of cholesteryl CETP esters to VLDL, IDL, LDL HDL Mediates reverse cholesterol transport from peripheral tissues to liver. Acts as a repository for apolipoproteins C and E (which are needed for chylomicron and VLDL metabolism). Secreted from both liver and intestine. Alcohol • synthesis. HDL is Healthy.


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First_Aid_Step1. Abetalipoproteinemia Autosomal recessive. Mutation in gene that encodes microsomal transfer protein (MTP). Chylomicrons, VLDL, LDL absent. Deficiency in ApoB-48, ApoB-100. Affected infants present with severe fat malabsorption, steatorrhea, failure to thrive. Later manifestations include retinitis pigmentosa, spinocerebellar degeneration due to vitamin E deficiency, progressive ataxia, acanthocytosis. Intestinal biopsy shows lipid-laden enterocytes. Treatment: restriction of long-chain fatty acids, large doses of oral vitamin E. “I hate to disappoint you, but my rubber lips are immune to your charms.” —Batman & Robin “The fully engaged heart is the antibody for the infection of violence.”


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First_Aid_Step1. “I hate to disappoint you, but my rubber lips are immune to your charms.” —Batman & Robin “The fully engaged heart is the antibody for the infection of violence.” Learning the components of the immune system and their roles in host defense at the cellular level is essential for both the understanding of disease pathophysiology and clinical practice. Know the immune mechanisms of responses to vaccines. Both congenital and acquired immunodeficiencies are very testable. Cell surface markers are high yield for understanding immune cell interactions and for laboratory diagnosis. Know the roles and functions of major cytokines and chemokines. Lymph node A 2° lymphoid organ that has many afferents, 1 or more efferents. Encapsulated, with trabeculae B . Functions are nonspecific filtration by macrophages, circulation of B and T cells, and immune response activation.


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First_Aid_Step1. Lymph node cluster Cervical, supraclavicular Head and neck Upper respiratory tract infection Infectious mononucleosis Kawasaki disease Mediastinal Trachea and esophagus Pulmonary TB Sarcoidosis (bilateral) 1° lung cancer Granulomatous disease Axillary Upper limb, breast, skin above umbilicus Mastitis Metastasis (especially breast cancer) Hilar Lungs Celiac Liver, stomach, spleen, pancreas, upper duodenum Superior mesenteric Lower duodenum, jejunum, ileum, colon to splenic fexure Inferior mesenteric Colon from splenic fexure to upper rectum Para-aortic Testes, ovaries, kidneys, uterus Metastasis Internal iliac External iliac Cervix, superior bladder, and body of uterus Lower rectum to anal canal (above pectinate line), bladder, vagina (middle third), cervix, prostate Superfcial inguinal Palpable lymph node Non-palpable lymph node Popliteal Right lymphatic duct drains right side of body above diaphragm into junction of the right Dorsolateral foot, posterior calf Lateral foot/leg


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First_Aid_Step1. Palpable lymph node Non-palpable lymph node Popliteal Right lymphatic duct drains right side of body above diaphragm into junction of the right Dorsolateral foot, posterior calf Lateral foot/leg cellulitis Anal canal (below pectinate line), skin below umbilicus (except popliteal area), scrotum, vulva Sexually transmitted infections Medial foot/leg cellulitis (superfcial inguinal) Mesenteric lymphadenitis Typhoid fever Ulcerative colitis Celiac disease Area of body drained Associated pathology


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First_Aid_Step1. Thoracic duct drains below the diaphragm and left thorax and upper limb into junction of left subclavian and internal jugular veins (rupture of thoracic duct can cause chylothorax) Spleen Located in LUQ of abdomen, anterolateral to left kidney, protected by 9th-11th ribs. Sinusoids are long, vascular channels in red pulp (red arrows in A ) with fenestrated “barrel hoop” basement membrane. T cells are found in the periarteriolar lymphatic sheath (PALS) within the white pulp (white arrows in A ). B cells are found in follicles within the white pulp. The marginal zone, in between the red pulp and white pulp, contains macrophages and specialized B cells, and is where antigen-presenting cells (APCs) capture blood-borne antigens for recognition by lymphocytes. Splenic macrophages remove encapsulated bacteria.


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First_Aid_Step1. Splenic macrophages remove encapsulated bacteria. Splenic dysfunction (eg, postsplenectomy state, sickle cell disease autosplenectomy):  IgM  complement activation  C3b opsonization  susceptibility to encapsulated organisms. Postsplenectomy blood findings: Thrombocytosis (loss of sequestration and removal) Lymphocytosis (loss of sequestration) Vaccinate patients undergoing splenectomy or with splenic dysfunction against encapsulated organisms (pneumococci, Hib, meningococci). Located in the anterosuperior mediastinum. Site of T-cell differentiation and maturation. Encapsulated. Thymus epithelium is derived from Third pharyngeal pouch (endoderm), whereas thymic lymphocytes are of mesodermal origin. Cortex is dense with immature T cells; Medulla is pale with Mature T cells and Hassall corpuscles A containing epithelial reticular cells. B , involutes by age 3 years. seen in some immunodeficiencies (eg, SCID, DiGeorge syndrome).


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First_Aid_Step1. B , involutes by age 3 years. seen in some immunodeficiencies (eg, SCID, DiGeorge syndrome). Thymoma—neoplasm of thymus. Associated with myasthenia gravis, superior vena cava syndrome, pure red cell aplasia, Good syndrome. Innate vs adaptive immunity HLA subtypes associated with diseases Functions of natural Lymphocyte member of innate immune system. killer cells Use perforin and granzymes to induce apoptosis of virally infected cells and tumor cells. Activity enhanced by IL-2, IL-12, IFN-α, and IFN-β. Induced to kill when exposed to a nonspecific activation signal on target cell and/or to an absence of MHC I on target cell surface. Also kills via antibody-dependent cell-mediated cytotoxicity (CD16 binds Fc region of bound IgG, activating the NK cell). Major functions of B and T cells


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First_Aid_Step1. Major functions of B and T cells B cells Humoral immunity. Recognize and present antigen—undergo somatic hypermutation to optimize antigen specificity. Produce antibody—differentiate into plasma cells to secrete specific immunoglobulins. Maintain immunologic memory—memory B cells persist and accelerate future response to antigen. T cells Cell-mediated immunity. CD4+ T cells help B cells make antibodies and produce cytokines to recruit phagocytes and activate other leukocytes. CD8+ T cells directly kill virus-infected and tumor cells via perforin and granzymes (similar to NK cells). Delayed cell-mediated hypersensitivity (type IV). Acute and chronic cellular organ rejection. Rule of 8: MHC II × CD4 = 8; MHC I × CD8 = 8. Differentiation of T cells Cytotoxic T cell Helper T cell IL-6 TGF-˜, IL-1, IL-6 IFN-° IFN-°, IL-4 TGF-˜, IL-2 IFN-°, IL-12 IL-4, IL-10 IL-2, IL-4 IFN-°, IL-2 Activate macrophages and cytotoxic T cells IL-4, IL-5, IL-6 Activate eosinophils, IL-10, IL-13 ˙ IgE


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First_Aid_Step1. IFN-°, IL-2 Activate macrophages and cytotoxic T cells IL-4, IL-5, IL-6 Activate eosinophils, IL-10, IL-13 ˙ IgE IL-17, IL-21, IL-22 Induce neutrophilic infammation TGF-˜, IL-10, IL-35 Prevent autoimmunity (maintain tolerance) CD4 Tand B-cell activation APCs: B cells, dendritic cells, Langerhans cells, macrophages. Two signals are required for T-cell activation, B-cell activation, and class switching. Th-cell activation as above. R B-cell receptor–mediated endocytosis. Exogenous antigen is presented on MHC II and recognized by TCR on Th cell. CD40 receptor on B cell binds CD40 ligand (CD40L) on Th cell. Th cells secrete cytokines that determine Ig class switching of B cells. B cells are activated, undergo class switching and affinity maturation, and begin producing antibodies.


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First_Aid_Step1. Antibody structure and function Fab (containing the variable/hypervariable regions) consisting of light (L) and heavy (H) chains recognizes antigens. Fc region of IgM and IgG fixes complement. Heavy chain contributes to Fc and Fab regions. Light chain contributes only to Fab region. VHJHJLDVLHinge Complement binding Macrophage binding Fc region C = Constant V = Variable SS = Disulfde bond Fab regionHypervariable regionsCLCLCH1CH1CH2CH3CH2CH3SS SS SS SS Light chain Heavy chain Epitope Fab: Fragment, antigen binding Complement binding • Determines idiotype: unique antigen-binding pocket; only 1 antigenic specificity expressed per B cell Fc (5C’s): • Confers (determines) isotype (IgM, IgD, etc) Generation of antibody diversity (antigen independent) 1. Random recombination of VJ (light-chain) or V(D)J (heavy-chain) genes 2. Random addition of nucleotides to DNA during recombination by terminal deoxynucleotidyl transferase (TdT) 3.


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First_Aid_Step1. Random recombination of VJ (light-chain) or V(D)J (heavy-chain) genes 2. Random addition of nucleotides to DNA during recombination by terminal deoxynucleotidyl transferase (TdT) 3. Random combination of heavy chains with light chains Generation of antibody specificity (antigen dependent) 4. 5. ComplementactivationMembrane attack complex (MAC) Antibody activates complement, enhancing opsonization and lysis C3b OpsonizationNeutralizationAntibody prevents bacterial adherence Antibody promotes phagocytosis IgG Main antibody in 2° response to an antigen. Most abundant isotype in serum. Fixes complement, opsonizes bacteria, neutralizes bacterial toxins and viruses. Only isotype that crosses the placenta (provides infants with passive immunity that starts to wane after birth). “IgGGreets the Growing fetus.”


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First_Aid_Step1. Prevents attachment of bacteria and viruses to mucous membranes; does not fix complement. Monomer (in circulation) or dimer (with J chain when secreted). Crosses epithelial cells by transcytosis. Produced in GI tract (eg, by Peyer patches) and protects against gut infections (eg, Giardia). Most produced antibody overall, but has lower serum concentrations. Released into secretions (tears, saliva, mucus) and breast milk. Picks up secretory component from epithelial cells, which protects the Fc portion from luminal proteases. IgM Produced in the 1° (immediate) response to an antigen. Fixes complement. Antigen receptor on the surface of B cells. Monomer on B cell, pentamer with J chain when secreted. Pentamer enables avid binding to antigen while humoral response evolves. IgD Unclear function. Found on surface of many B cells and in serum.


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First_Aid_Step1. IgD Unclear function. Found on surface of many B cells and in serum. IgE Binds mast cells and basophils; cross-links when exposed to allergen, mediating immediate (type I) hypersensitivity through release of inflammatory mediators such as histamine. Contributes to immunity to parasites by activating eosinophils. Opsonins—C3b and IgG are the two 1° Opsonin (Greek) = to prepare for eating. opsonins in bacterial defense; enhance phagocytosis. C3b also helps clear immune complexes. Inhibitors—decay-accelerating factor (DAF, aka CD55) and C1 esterase inhibitor help prevent complement activation on self cells (eg, RBCs). Spontaneous and microbial surfaces Amplifes generation of C3b called C2a but is now referred to as C2b. C3 C3b B D Bb C3 C3aC3aC3bBb (C3 convertase) C3C2b C4b C2 C1 C4 C4a(C3 convertase) C1 C5 C5aC5b C6-C9 C3bBb3b (C5 convertase) C4b2b3b (C5 convertase) C4b2b C3bcomplex C1-like * * *Historically, the larger fragment of C2 was Lysis, (C5b-9) (eg, mannose)


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First_Aid_Step1. Lysis, (C5b-9) (eg, mannose) C1 esterase inhibitor Causes hereditary angioedema due to unregulated activation of kallikrein  bradykinin. deficiency Characterized by  C4 levels. ACE inhibitors are contraindicated (also  bradykinin). Paroxysmal nocturnal A defect in the PIGA gene preventing the formation of glycosylphosphatidylinositol (GPI) anchors for hemoglobinuria complement inhibitors, such as decay-accelerating factor (DAF/CD55) and membrane inhibitor of reactive lysis (MIRL/CD59). Causes complement-mediated intravascular hemolysis  haptoglobin, dark urine A . Important cytokines Acute (IL-1, IL-6, TNF-α), then recruit (IL-8, IL-12).


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First_Aid_Step1. A . Important cytokines Acute (IL-1, IL-6, TNF-α), then recruit (IL-8, IL-12). Respiratory burst Also called oxidative burst. Involves the activation of the phagocyte NADPH oxidase complex (eg, in neutrophils, monocytes), which utilizes O2 as a substrate. Plays an important role in the immune response  rapid release of reactive oxygen species (ROS). NADPH plays a role in both the creation and neutralization of ROS. Myeloperoxidase contains a blue-green, heme-containing pigment that gives sputum its color. Phagocytes of patients with CGD can utilize H2O2 generated by invading organisms and convert it to ROS. Patients are at  risk for infection by catalase ⊕ species (eg, S aureus, Aspergillus) capable of neutralizing their own H2O2, leaving phagocytes without ROS for fighting infections.


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First_Aid_Step1. Pyocyanin of P aeruginosa generates ROS to kill competing pathogens. Oxidative burst also leads to K+ influx, which releases lysosomal enzymes. Lactoferrin is a protein found in secretory fluids and neutrophils that inhibits microbial growth via iron chelation. Interferons IFN-α, IFN-β, IFN-γ mechanISm A part of innate host defense, interferons interfere with both RNA and DNA viruses. Cells infected with a virus synthesize these glycoproteins, which act on local cells, priming them for viral defense by downregulating protein synthesis to resist potential viral replication and by upregulating MHC expression to facilitate recognition of infected cells. Also play a major role in activating antitumor immunity. clInIcal uSe Chronic HBV, Kaposi sarcoma, hairy cell leukemia, condyloma acuminatum, renal cell carcinoma, malignant melanoma, multiple sclerosis, chronic granulomatous disease.


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First_Aid_Step1. clInIcal uSe Chronic HBV, Kaposi sarcoma, hairy cell leukemia, condyloma acuminatum, renal cell carcinoma, malignant melanoma, multiple sclerosis, chronic granulomatous disease. adVerSe eFFectS Flu-like symptoms, depression, neutropenia, myopathy, interferon-induced autoimmunity. T cells TCR (binds antigen-MHC complex) CD3 (associated with TCR for signal transduction) CD28 (binds B7 on APC) Helper T cells CD4, CD40L, CXCR4/CCR5 (co-receptors for HIV) Anergy State during which a cell cannot become activated by exposure to its antigen. T and B cells become anergic when exposed to their antigen without costimulatory signal (signal 2). Another mechanism of self-tolerance. Vaccination Induces an active immune response (humoral and/or cellular) to specific pathogens. Hypersensitivity types Four types (ABCD): Anaphylactic and Atopic (type I), AntiBody-mediated (type II), Immune Complex (type III), Delayed (cell-mediated, type IV). Types I, II, and III are all antibody-mediated.