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1. All of the following statements about O-linked glycoproteins are true EXCEPT: A. B. C. D. E. 2. Cystic fibrosis patients are frequently on antibiotics for infections. Antibiotics increase the chances for deficiency in which one of the following vitamins? A. B. C. D. E. 3. Vitamin A Vitamin C Vitamin D Vitamin E Vitamin K All of the following steps take place in insulin biosynthesis EXCEPT: A. B. C. D. E. 4. The carbohydrate component can be branched and can contain many different monosaccharides. The carbohydrate is attached directly to a growing oligosaccharide linked to the protein through either scrine or threonine. Activated sugars are added to protein only in the Golgi. Degradation of both the protein and oligosaccharide components occurs in the lysosomes. The oligosaccharide component of all O-linked glycoproteins contains a common leader sequence attached directly to the protein. Insulin mRNA contains signal colons. The A and B chains of insulin are held together by two interchain disulfide bonds. Disulfide bond formation occurs in the cytosol. Mature insulin is stored in secretory granules. Release of insulin into the circulation is a highly regulated process involving Ca2+-dependent exocytosis. Ascorbic acid is associated with all of the following processes EXCEPT: A. B. C. D. E. Iron absorption from the intestine Participation in hydroxylation reactions in the synthesis of collagen Wound healing Inactivation of oxygen free radicals in aqueous environments Inactivation of lipid peroxides in membranes 1 5. All of the following statements about glycosaminoglycans and proteoglycans are true EXCEPT: A. B. C. D. E. 6. Transport by simple diffusion is characterized by all of the following EXCEPT: A. B. C. D. E. 7. A ceramide structure A fatty acid One or more sialic acids Glucose or galactose All of the following can lead to hyperbilirubinemia EXCEPT: A. B. C. D. E. 9. Nonsaturablc increase as a function of concentration Lacks stereospecificity Increases as a function of lipid solubility Can be abolished by a single mutation Does not result in movement against a concentration gradient A cerebroside may contain all of the following EXCEPT: A. B. C. D. 8. Hyaluronic acid and aggrecan form a non-covalent complex held together by a link protein. Sulfate is added to the growing oligopolysaccharide chain of proteoglycans by PAPS (3'-phosphoadenosine 5'-phosphosulfate). Glycosaminoglycans are I00% polysaccharide while proteoglycans are composed of mostly polysaccharide with a small amount of protein. Formation of iduronic acid occurs after addition of glucuronic acid to the growing oligosaccharide chain. The glycosaminoglycan hyaluronic acid is assembled in the Golgi. Elevations in uric acid Liver Disease Hemolytic crises Blockage of the bile duct Premature birth Which of the following enzymes in the heme biosynthetic pathway is inhibited by lead? A. B. C. D. E. Protoporphyrinogen oxidase Uroporphyrinogcn III cosynthase δ-aminolevulinic acid dehydratase Porphobilinogen deaminase δ-aminolevulinic acid synthase 2 10. The carbon atoms of aspartate are derived directly from: A. B. C. D. E. 11. All of the following statements about cholesterol in membranes are true EXCEPT: A. B. C. D. E. 12. Cholesterol increases the phase transition temperature of membranes containing mostly unsaturated fatty acid side chains. Cholesterol is more abundant in the plasma membrane than mitochondrial membranes. The cholesterol content of a membrane has no influence on the rate of ion transport by a carrier-type ionophore. Cholesterol is absent from bacterial membranes. The hydroxyl group of cholesterol in membranes is in contact with the aqueous phase. All of the following statements concerning iron utilization in the body are true EXCEPT: A. B. C. D. E. 13. Methionine Serine Homocysteine Oxaloacetate Tetrahydrobiopterin A clathrin-mediated process is involved in iron uptake into cells. Ferrous (Fe2+) iron is transported in serum bound to transferrin. Ferrous (Fe2+) iron is the form preferentially absorbed in the intestine. Intracellular iron is stored in the liver as the ferric form (Fe3+) bound to ferritin. Some iron is released into the intestine due to secretion in bile. Binding of gonadotrophin-releasing hormone to its receptor in the anterior pituitary leads to all of the following responses EXCEPT: A. B. C. D. E. Activation of a G protein Activation of phospholipase C Activation of protein kinase C Decrease in cytosolic Ca2+ Release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the cell 3 14. All of the following diseases are due to a defect in lysosomal degradation of a sphingolipid EXCEPT: A. B. C. D. E. 15. Which of the following reactions uses S-adenosylmethionine as a direct methyl donor? A. B. C. D. E. 16. The conversion of methylmalonyl CoA to succinyl CoA The methylation of dUMP to form dTMP The methylation of homocysteine to form methionine The formation of 5,10-methylene-FH4 from serine The methylation of guanidinoacetate to form creatine All of the following statements concerning vitamin D are correct EXCEPT: A. B. C. D. E. 17. Hurler Gaucher's Tay-Sachs Nieman-Pick Fabry's In skin, 7-dehydrocholesterol is converted to cholcealciferol by the action of mixed function oxidases. In kidney, formation of calcitrol (active vitamin D) is stimulated by parathyroid hormone. Vitamin D inhibits renal excretion of Ca2+. High levels of Ca2+ in the blood decrease formation of the active vitamin. Vitamin D stimulates Ca2+ absorption in the intestine. The protein that plays a role in the transfer of cholesterol from extrahepatic tissue to HDLs is: A. B. C. D. E. Apolipoprotein A Apolipoprotein B-100 Apolipoprotein B-48 Apolipoprotein C Apolipoprotein E 4 18. Non-Steroidal Anti-Inflammatory Drugs (NSAID) reduce the cellular levels of all of the following EXCEPT: A. B. C. D. 19. Folate is reduced to tetrahydrofolic acid by a reaction catalyzed by the enzyme: A. B. C. D. E. 20. Dihydrofolate reductase Methotrexate reductase Thymidylate synthetase Dihydropteridine reductase Ribonucleotide reductase With respect to bile acids/salts all of the following are true EXCEPT: A. B. C. D. E. 21. Prostacyclin Prostaglandin H2 (PGH2) Arachidonic acid Thromboxane Secondary refers to those bile acids/salts that are sulfated in the liver. Primary refers to those bile acids/salts that are initially made in the liver. The rate limiting step in their synthesis is stimulated by cholesterol. Conjugation of bile salts with glycine or taurine increases their solubility in water. Incomplete reabsorption of bile salts/acids is a mechanism for elimination of cholesterol. All of the following statements about phosphatidylserine are true EXCEPT: A. B. C. D. It is a major precursor in sphingolipid biosynthesis. It can be made by reaction of serine with phosphatidylcholine. It can be converted to phosphatidylethanolamine by decarboxylation. It is an intermediate in a cycle that produces ethanolamine in a net fashion. 22. Tyrosine can be produced from which of the following amino acids? A. B. C. D. E. Glutamate Phenylalanine Proline Methionine Serine 5 23. Which of the following DOES NOT provide carbon(s) to the building of the purine ring structure? A. B. C. D. E. 24. All of the following statements about steroid hormone receptors are true EXCEPT: A. B. C. D. E. 25. The receptor contains a DNA binding domain that binds zinc at specific sites. The hormone-receptor complex binds to specific response elements in genes leading to activation of transcription. Receptors contain a tyrosine kinase that is activated by hormone binding. The steroid hormone binds its receptor intracellularly. Hormone binding to its receptor is saturable. The signaling pathways triggered by epidermal growth factor and insulin share all of the following characteristics in common EXCEPT: A. B. C. D. E. 26. Glycine Methenyl-FH4 CO2 Formyl-FH4 Glutamine Receptor activation results in autophosphorylation of intracellular tyrosine kinase domains of the receptor. Hormone-receptor complexes are internalized into the cell by clathrin-mediated endocytosis. Binding of hormone causes dimerization of the receptor. Both hormones contain at least one intrachain disulfide bond. Receptor activation leads to a cascade of intracellular phosphorylations. The two enzymes that require vitamin B12 cofactors are: A. B. C. D. E. Methylmalonyl CoA mutase and mammalian ribonucleotide reductase. Cystathionine synthase and mammalian ribonucleotide reductase. Methylmalonyl CoA mutase and methionine synthase. Mammalian ribonucleotide reductase and thymidylate synthase. Cystathionine synthase and thymidylate synthase. 6 27. All of the following statements concerning membrane transport processes are true EXCEPT: A. B. C. D. E. 28. Which of the following is TRUE of both proteoglycans and glycoproteins? A. B. C. D. 29. The saccharide component of both proteoglycans and glycoproteins can be branched. Polysaccharides of both glycoproteins and proteoglycans are made up of repeating disaccharide units. Polysaccharides of both proteoglycans and glycoproteins can contain sialic acid. The protein component of both proteoglycans and glycoproteins is synthesized in the endoplasmic reticulum. VLDLs are synthesized in the liver for transport of which of the following to adipose tissue: A. B. C. D. E. 30. The protein defective in cystic fibrosis is a chloride channel containing two ATP binding domains. Resistance to chemotherapy drugs in cancer cells can occur by gene amplification of an endogenous ATP-dependent transporter. Ca2+ transporters in the endoplasmic reticulum utilize ATP hydrolysis to maintain cytosolic Ca2+ levels. The plasma membrane Na+/K+-ATPase transports 3 Na out of the cell for every 2 K+ it transports into the cell. Glucose uptake into red blood cells is a Na+-dependent process. Triacylglycerols LDL receptors Apolipoproteins for HDL synthesis Apolipoprotein B-100 Phospholipids Which one of the following treatments would INCREASE secondary active transport of glucose into kidney and intestinal epithelial cells? A. B. C. D. E. Addition of ouabain Decrease intracellular K+ levels Decrease intracellular Na+ levels Addition of a glucose analog Decrease in intracellular ATP levels 7 31. All of the following are involved in transfer of dietary triacylglycerol from the intestine to the adipose EXCEPT: A. B. C. D. E. 32. Cellular energy generation is severely compromised in thiamine deficiency because thiamine pyrophosphate is: A. B. C. D. E. 33. A major cofactor for most oxidation-reduction reactions An essential cofactor for pyruvate and α-ketoglutarate dehydrogenases A cofactor for amino acid decarboxylases Necessary for utilizing amino acids for energy via transamination Necessary for oxidation of alcohol The most direct route to phosphatidylinositol biosynthesis is: A. B. C. D. E. 34. Chylomicrons Apolipoprotein B-48 Lipoprotein lipase Apolipoprotein C-II Lecithin:Cholesterol Acyl Transferase Inositol phosphate + phosphatidic acid CDP-inositol + 1,2-diacylglycerol CDP-diacylglycerol + inositol Phosphatidyicholine + inositol Inositol + ATP + 1,2-diacylglycerol All of the following statements concerning lipids in membranes are true EXCEPT: A. B. C. D. E. In mammalian cells, cardiolipin is found predominantly in the mitochondrial membrane. Free fatty acids are largely absent from cell membranes. Sphingomyelin is a major component of bacterial membranes. An increase in chain length of fatty acyl residues of lipids makes the membrane less fluid. Carbohydrate-containing lipids are largely found in the plasma membrane of mammalian cells. 8 35. Which one of the following changes would you expect in a patient with a deficiency in the B-48:E receptor? A. B. C. D. E. 36. All of the following statements about the regulation of cholesterol biosynthesis are true EXCEPT: A. B. C. D. 37. HMG CoA reductase levels are regulated by a transcription activator released from the Golgi by proteolysis. Stating reduce cholesterol biosynthesis by inhibiting HMG CoA reductase. HMG CoA reductase levels are reduced by its proteolysis stimulated by sterol derivatives. The Sterol Regulatory Element Binding Protein only activates transcription of the gene encoding HMG CoA reductase. Lesch-Nyhan Syndrome is associated with a deficiency in: A. B. C. D. E. 38. Elevation of both serum HDL and LDL Elevation of serum LDL only Elevation of serum HDL only Elevation of both serum chylomicrons and VLDL Elevation of serum chylomicron remnants only Adenosine deaminase Hypoxanthine-guanine phosphoribosyltransferase Orotate phosphoribosyltransferase Orotidine decarboxylase Adenine phosphoribosyltransferase The carbons of glycine are used in the formation of 1. 2. 3. 4. A. B. C. D. E. Creatine Heme Adenosine monophosphate Tyrosine 1, 2, 3 only 1, 3 only 2, 4 only 4 only All of the above 9 39. Which of the following molecules is a product of pyrimidine degradation? A. B. C. D. E. 40. Which ONE of the following individuals would most likely be in nitrogen equilibrium? A. B. C. D. E. 41. A normal adult male A normal pregnant female A growing child An adult male recovering from surgery A normal female on a very low protein diet In the biosynthesis of cell membrane proteins, each of the following steps occurs EXCEPT: A. B. C. D. E. 42. ß-Aminoisobutyrate Xanthine Uric acid Allopurinol Orotate Signal recognition particles binds to the signal codons of mRNA's encoding membrane or secreted proteins. Docking of ribosomes to the endoplasmic reticulum membrane involves a GTP/GDP cycle. Specialized proteins catalyze folding of the nascent polypeptide chains. Chain elongation and translocation of the nascent polypeptide through a pore in the endoplasmic reticulum membrane are separate but simultaneous processes. Many mitochondrial proteins are encoded in the nucleus and are made in the cytosol on free ribosomes. Which of the following statements about serine is TRUE? A. B. C. D. E. It is converted to pyruvate and urea by a dehydratase. It may be synthesized from glucose via an intermediate of the TCA cycle. It is converted to glycine by a reaction requiring tetrahydrofolate. It is the only amino acid that contains a hydroxyl group. It is an essential amino acid. 10 43. In de novo synthesis of cholesterol by the liver all of the following are true EXCEPT: A. B. C. D. 44. All of the following statements about N-linked glycoproteins are true EXCEPT: A. B. C. D. 45. Phosphatidylinositol Sphingomyelin Ceramide Leukotriene C4 Prostacyclin All of the following treatments will tend to increase intracellular cyclic AMP levels EXCEPT: A. B. C. D. E. 47. The carbohydrate component contains a common oligosaccharide made up of mannose and N-acetyl glucosamine (GIcNAc). Formation of the oligosaccharide component occurs in both the endoplasmic reticulum and the Golgi. The elongation of the protein-linked oligosaccharide in the Golgi requires dolichol phosphate. Nucleotide-activated sugars required for synthesis of the oligosaccharide component are synthesized in the cytoplasm. Glycerol is present in which one of the following? A. B. C. D. E. 46. Farnesyl pyrophosphate is the immediate precursor to squalene. All of the carbons are supplied by 18 acetyl-CoA's. The precursor HMG-CoA is synthesized in the mitochondrial matrix. Several reactions involve mixed function oxidases. Addition of epinephrine Addition of caffeine Addition of cholera toxin Addition of diptheria toxin Inhibition of the intrinsic GTPase activity of a Gs protein All of the following statements concerning G proteins involved in intracellular signaling are true EXCEPT: A. B. C. D. E. Certain oncogenes result from mutations in a G protein. Cholera toxin action is associated with covalent modification of a G protein. All G proteins contain an intrinsic GTPase activity. Pertussis toxin is associated with covalent modification of a G protein. All G proteins are monomeric. 11 Medical School Biochemistry Course EXAM ANSWER KEY BLOCK III Q# 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 V1 V2 V3 V4 C C E A B D E C A A C A B D E C C E E A E A D A C E C C A C A B A A C E C C D C B E C D C E B C C A D B A D A E C E E D C D A A A C A C C A C C A A A E D C A A A A A E A E B D C C E E E C C A A E C A C E C D D D E E E B D D E B A C D B C E E A E E E A B A A C C A A B C B E C E C E C D C C D B A D C A C C E A A E A A A E C A C A E C E A C C A B C C E A A A D D E D E E A E C 12 13