NBME – Biochemistry – Flashcards
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What is an α-carbon?
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The carbon next to the most oxidized group or The first carbon atom that attaches to a functional group
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Equilibrium constant equation = ?
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K = [H+][OH-]/[H2O]
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Ion product of H2O
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Kw = [H+][OH-] = 1x10^-14
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Henderson-Hasselbalch equation =
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pH = pK + log([A-]/[HA])
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What is the normal pH range or arterial blood?
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7.37-7.43
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Metabolic acidosis can result from...
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accumulation of metabolic acids (lactic acid or ketone bodies, β-hydroxybutyric acid, and acetoacetic acid) or ingestion of acids or compounds that are metabolized to acids (e.g. methanol, ethylene glycol)
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Metabolic alkalosis is due to...
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increased HCO3-
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What determines D and L configuration?
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the asymmetric carbon atom farthest from the aldehyde or ketone group. L if left, D if right
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What stereoisomers?
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have the same chemical formula but differ in the position of the hydroxyl groups on one or more of their asymmetric carbons *not mirror images*
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Enantiomers
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stereoisomers that are *mirror* images of each other
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Glycosidic bonds
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form when the hydroxyl group on the anomeric carbon of a monosaccharide reacts with an -OH of -NH group of another compound
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anomer
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Anomers are cyclic monosaccharides or glycosides that are epimers, differing from each other in the configuration of C-1 if they are aldoses or in the configuration at C-2 if they are ketoses.
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anomeric carbon
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The epimeric carbon in anomers are known as anomeric carbon or anomeric center.
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Oxidation of carbon 6 of a hexose forms...
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uronic acid
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oxidation of carbon 6 of glucose forms...
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glucuronic acid conjugation with glucuronic acid makes lipid compounds more water soluble
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What is the cause of *gray baby syndrome*?
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Infants have a decreased ability to conjugate glucuronic acid onto drugs such as *chloramphenicol*. Administration of this antibiotic during the neonatal period can result in elevated plasma levels of the drug and a feral shock-like syndrome, which is referred to as gray baby syndrome
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What are reducing sugars?
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reducing sugars contain a free anomeric carbon tat can be oxidized
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What are dipsticks and what is their purpose?
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they are used clinically to measure glucose in urine. enzyme: *glucose oxidase*
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How can polyols be formed from aldehydes or ketone groups on carbohydrates?
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by reducing them
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Patients with *leukocyte adhesion deficiency (LAD) II* have a congenital deficiency in the ability to do what?
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*glycosylate* ligands for cell surface selectins, which mediate immune cell migration addition of sugar moieties to proteins can alter proteins in many ways including modifying their functions
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Proteoglycans
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consist of a *core protein* with long unbranched polysaccharide chains (*glycosominoglycans*) attached
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What is an important use of heparin?
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anticoagulant
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Which drug might be used to treat MIs?
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heparin
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What are glycosaminoglycans usually composed of?
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uronic acid and hexosamine
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Glucose and Galactose are reduced to what, respectively?
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sorbitol galatitol
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Benedict test is for what?
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reducing sugars modified dipstick test also detects the presence of sucrose, galactose and fructose newborns urine is routinely screened for reducing sugars to detect *inborn errors of metabolism*
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What by product of glucose metabolism leads to cataracts?
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sorbitol sorbitol does not readily diffuse out of cells. As it accumulates in cells, it causes osmotic damage to cells of the nervous system, resulting in cataracts and neuropathy
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The influenza virus infects cells by binding to what on the surface of epithelial cells?
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sialic acid
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cerebrosides
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synthesized from ceramide and UDP-sugars
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ganglioside
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A sphingolipid with a head group containing an oligosaccharide and one or more N-acetylneuraminic acid (NANA) molecules.
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Is glycine excitatory or inhibitory?
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inhibitory
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All of the amino acids, except glycine, are of what configuration--D or L?
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L
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Essential amino acids
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Essential amino acids PVT. TIM HALL: *P*he *V*al *T*hr *T*rp *I*le *M*et *H*is *A*rg *L*eu *L*ys
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Which amino acids contain sulfur?
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Cysteine and Methionine
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Amides are present on the side chains of which amino acids?
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asparagine and glut*amine* (the ones that form acids)
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Characteristics of peptide bonds
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rigid and planar no freedom of rotation due to partial double-bond character However, bonds involving the α-carbon can rotate freely
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Polyunsaturated fatty acids are often classified according to the position of what?
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the first double bond from the ω-end (the carbon furthest from the carbonyl group)
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Sphingolipid
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Major membrane components Contains ceramide with a variety of groups attached
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Sphingomyelin
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ceramide + phosphocholine myelin sheath
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Cerebrosides
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ceramide + sugar
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Gangliosides
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ceramide + multiple sugar residues
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What type of sphingolipid is cholera related to clinically?
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ganglioside GM1 due to the fact that the toxin binds to the GM1 receptor on cells leading to watery diarrhea
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Which polyunsaturated fat gives rise to prostaglandins and leukotrienes?
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arachidonic acid which comes from linoleic acid
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Sickle cell results from what point mutation?
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glutamate → valine Since glu has a negative charge and val is neutral, this single amino acid difference (glu -> val) accounts for the difference in mobility during electrophoresis.
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Creutzfeldt-Jakob disease
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Result from the transmission of a proteinaceous agent that is capable of altering the normal *α-helical* arrangement of the prion protein and replacing it *β-pleated sheets* and smaller α-helices, similar to the pathogenic form The resulting misfolded protein is resistant to degradation, with death of the affected neurons. Patients suffer pronounced involuntary jerking movements (startle myoclonus) and rapidly *deteriorating dementia*
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Homeobox proteins contain what type of motifs?
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helix-turn-helix
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Mutations in α-antitrypsin (AAT) deficiency are a result of what?
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misfolded protein that gets trapped within the cell Patients with decreased levels of this protease inhibitor manifest wit cirrhosis and emphysema
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What type of repeats are found in Huntington's genes?
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poly*glutamine* repeats
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Ubiquitin is used as a marker for what?
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protein degradation by the proteosome
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What drug inhibits the proteosome?
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bortezomib (Velcade)
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PEST sequence
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proteins that have the pest sequence in their N terminus are targeted for rapid degradation after synthesis by non specific proteases
