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MedBiochem Exam 2, 1998For each of the following questions, choose the

one best answer. (Answer key and results of the exam liaison meeting are posted at the

bottom of the page.)

1. The principal apoprotein in LDL is

A. Apo A

B. Apo B100

C. Apo CII

D. Apo D

E. Apo E

2. Glucagon plays a homeostatic role in the body by

A. facilitating glucose uptake into skeletal muscle.

B. causing the activation of liver phosphorylase.

C. activating adenylate cyclase in skeletal muscle cells.

D. causing the activation of liver pyruvate dehydrogenase.

E. stimulating muscle glycogenolysis during intense exercise.

3. The major function of chylomicrons is transport of

A. cholesterol from the liver to peripheral cells.

B. dietary triglycerides to peripheral tissues.

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C. fatty acids from the adipose tissue to energy-requiring tissues suchas skeletal muscle.

D. endogenous triglycerides from the liver.

E. cholesterol from peripheral tissues to the liver for disposal.

4. Medium-chain triglycerides

A. are absorbed intact in the small intestine and are transported inthe thoracic duct to blood as chylomicrons.

B. are not utilized in man because of a lack of pancreatic lipasespecific for medium-chain triacylglycerols.

C. are absorbed intact in the small intestine and are transported inthe portal vein.

D. contain mostly fatty acids having a chain length of 14-16 carbons.

E. none of the above.

5. During uncontrolled insulin-dependent diabetes mellitus, ketosisresults primarily from

A. excessive mobilization of adipose fatty acids by hormone-sensitivelipase.

B. excessive conversion of muscle amino acids into proteins.

C. excessive release of glucose from glycogen.

D. excessive breakdown of triglycerides by adipose lipoprotein lipase.

E. inability to produce glucose from lactate.

6. The intrinsic and extrinsic pathways of blood coagulation convergeat the step involving the conversion of





A. prothrombin to thrombin.

B. factor X to Factor Xa.

C. fibrinogen to fibrin.

D. vitamin K to gamma-carboxyglutamic acid.

E. factor XIII to Factor XIIIa.

7. The rate-limiting enzyme in cholesterol biosynthesis is

A. isopentyl pyrophosphate isomerase.

B. mevalonate kinase.

C. hydroxymethylglutaryl-CoA reductase.

D. dimethylallyl transferase.

E. squalene synthase.

8. Increased plasma insulin can result in

A. increased adipocyte adenylate cyclase activity.

B. decreased adipocyte pyruvate dehydrogenase activity

C. increased muscle phosphorylase activity.

D. decreased hepatocyte glycogen.

E. decreased adipocyte hormone-sensitive lipase activity.

9. The substrates for the synthesis of deoxyribonucleoside phosphatesare

A. ribonucleosides.

B. ribonucleoside monophosphates.





C. ribonucleoside diphosphates.

D. ribonucleoside triphosphates.

10. N- and C-terminal peptides are removed from the procollagenmolecule by the action of procollagen peptidases. Which of thefollowing events immediately precedes this event?

A. Synthesis of collagen polypeptide chains

B. Hydroxylation of proline and lysine residues

C. Formation of the tropocollagen triple helix

D. Secretion into the extracellular space

E. Covalent cross-linking of the tropocollagen molecules

11. In mammals, phosphatidylserine is formed

A. from reaction of serine with CDP-diacylglycerol.

B. exchange of serine for the ethanolamine onphosphatidylethanolamine.

C. carboxylation of phosphatidylethanolamine.

D. reaction of diglyceride with CDP-serine.

12. The resting membrane potential (membrane polarization) of theneuron can be attributed, in part, to the relatively low permeability ofthe membrane to which cation?

A. Ca++

B. K+

C. Mg++





D. Na+

E. SO4=

13. Which of the following reactions in EXTRAHEPATIC tissues isneeded for utilization of acetoacetate?

A. decarboxylation of acetoacetate to acetone

B. carboxylation of acetoacetate

C. reduction of acetoacetate to beta-hydroxybutyrate

D. transfer of coenzyme A from succinyl CoA to acetoacetate

E. condensation of beta-hydroxybutyrate with acetyl CoA to formHMG CoA

14. 5-Phosphoribosyl-1-pyrophosphate (PRPP) is an intermediate in

A. the de novo synthesis of purine nucleotides.

B. the de novo synthesis of pyrimidine nucleotides.

C. the salvage pathway for the synthesis of purine nucleotides.

D. A and C.

E. A, B and C.

15. The principal lung surfactant is

A. phosphatidylcholine.

B. phosphatidylinositol.

C. phosphatidic acid.





D. cardiolipin.

E. sphingomyelin.

For each of the following questions, choose the one best answer.

16. All the statements concerning phosphatidyl choline (lecithin) aretrue EXCEPT

A. It possesses three fatty acyl groups in its structure.

B. It can be synthesized using S-adenosyl methionine as anintermediate.

C. It can be synthesized using a CDP-derivative as an intermediate.

D. It is found in most lipoproteins.

E. It is an integral part of membranes.

17. The first reaction of porphyrin biosynthesis requires glycine and

A. acetyl-CoA.

B. malonyl-CoA.

C. succinyl-CoA.

D. UDP-glucose.

E. free coenzyme A.

18. The specific Ca2+ binding protein of the myofibril of skeletalmuscle is:

A. actin

B. tropomyosin





C. troponin

D. calmodulin

E. myosin

19. Tetrahydrobiopterin is a cofactor required for which one of thefollowing conversions?

A. Dihydrofolate -> tetrahydrofolate

B. Phenylalanine -> tyrosine

C. Methionine -> cysteine

D. Phenylalanine -> phenylpyruvate

E. None of the above.

20. All of the following are likely to occur after eating a large amountof carbohydrate EXCEPT

A. the synthesis of triacylglycerol in the liver.

B. the synthesis of glycogen in the liver.

C. increased production of NADPH by the pentose phosphatepathway in liver.

D. lipolysis in adipose tissue.

E. the synthesis and release of VLDL from the liver.

21. All of the following are true statements about lipoprotein lipaseactivity EXCEPT

A. circulating VLDL triglycerides are a substrate for lipoproteinlipase.





B. lipoprotein lipase is a protein.

C. lipoprotein lipase can convert triglycerides of VLDL to fatty acids.

D. the free fatty acids released by lipoprotein lipase can be used forbeta-oxidation by muscle mitochondria.

E. lipoprotein lipase requires bile salts for activity.

22. Activation of the insulin receptor involves autophosphorylation of

A. serine

B. threonine

C. tyrosine

D. histidine

E. aspartate

23. The carbon atom in urea arises from

A. aspartate.

B. carbon dioxide.

C. alanine.

D. pyruvate.

E. glutamate.

24. Chemically, the estrogens are characterized by

A. a 21 carbon steroid skeleton.

B. a lack of a methyl group at C-10.

C. an aromatic A ring.





D. a lack of a hydroxyl group at C-17.

E. all of the above.

25. CTP is an important nucleotide in the biosynthesis of

A. phosphatidylcholine.

B. acetoacetate.

C. triglyceride (triacylglycerol).

D. phosphatidic acid.

E. cholesterol.

26. A deficiency of vitamin B12 in humans results in anemia primarilybecause

A. vitamin B12 is required for the conversion of methylmalonyl CoAto succinyl CoA.

B. vitamin B12 is necessary for the absorption of folic acid from thegut.

C. vitamin B12 is required for the conversion of 5-methyl-tetrahydrofolate (THF) to THF.

D. vitamin B12 is required for the conversion of methionine tocysteine.

E. vitamin B12 is a cofactor in the biosynthesis of purine nucleotidesrequired for the synthesis of DNA.

27. Twenty four hours after a meal, the primary source of glucose forthe brain is:





A. input to the blood from the hepatic portal vein.

B. breakdown of muscle glycogen.

C. extrahepatic synthesis of ketones.

D. mobilization of fatty acids.

E. hepatic gluconeogenesis.

28. Glycine and cysteine both

A. are precursors of the porphyrin ring.

B. are precursors of glutathione.

C. are essential amino acids.

D. give rise to hippuric acids in the course of detoxication reactions.

E. are ketogenic.

29. Each of the following is involved in purine salvage reactionsEXCEPT which one?

A. adenine

B. PRPP

C. hypoxanthine

D. orotate

E. guanine

30. A protein involved in the dissolution of blood clots is

A. thrombin.

B. plasmin.





C. antithrombin III.

D. factor XIIIa.

E. heparin.

31. The most dramatic increases in serum alanine transaminase(SGPT or ALT) levels occur in patients with

A. biliary obstruction.

B. hemolysis.

C. malabsorption of fat-soluble vitamins.

D. inflammatory diseases of the liver.

E. intrahepatic cholestasis.

32. Which of the following residues can be converted to aldehydecrosslinks in collagen?

A. Hydroxylysine

B. Proline

C. Lysine

D. Aspartate

E. Desmosine

33. Derivatives of tetrahydrofolic acid participate in the synthesis ofeach of the following EXCEPT

A. adenosine triphosphate.

B. guanosine triphosphate.





C. thymidine triphosphate.

D. cytidine triphosphate.

E. S-adenosylmethionine.

34. A low serum haptoglobin level would be likely to result from

A. iron deficiency.

B. intravascular hemolysis.

C. extravascular hemolysis.

D. pernicious anemia.

E. failure to mobilize iron stores.

35. Which of the following compounds has aperhydrocyclopentanophenanthrene ring in its structure?

A. Arachidonic acid

B. Cholesterol

C. Ganglioside

D. Squalene

E. Vitamin A

36. In nature most glycosaminoglycans (mucopolysaccharides) arefound covalently linked to protein cores. Which of the following isnot?

A. hyaluronic acid

B. chondroitin sulfate





C. heparin

D. dermatan sulfate

E. heparan sulfate

37. Which of the following is the major carrier for the transport ofcholesterol to peripheral tissues?

A. chylomicron

B. VLDL

C. LDL

D. HDL

E. albumin

38. The enzyme in porphyrin biosynthesis which is stimulated in acuteattacks of porphyria is the step catalyzed by:

A. delta-amino levulinic acid synthase.

B. uroporphyrinogen III cosynthase.

C. porphobilinogen deaminase.

D. coproporphyrinogen III oxidase.

E. ferrochelatase.

39. Which of the following is an intermediate in fatty acid synthesis inthe cytoplasm?

A. malonyl-CoA

B. succinyl-CoA





C. phosphatidic acid

D. acetoacetic acid

E. malic acid

40. Which of the following compounds serves as a coenzyme fortransaminase reactions?

A. pyridoxal phosphate

B. thiamine pyrophosphate

C. nicotinamide adenine dinucleotide

D. flavin adenine dinucleotide

E. coenzyme A

41. Which of the following substances is an intermediate in thesynthesis of both triglycerides and phosphoglycerides?

A. phosphatidic acid

B. CDP-choline

C. fatty aldehydes

D. phosphatidylinositol

E. cholesterol

42. Fatty acids from adipose tissue are transported to sites ofutilization in the form of

A. triglycerides bound to serum albumin.

B. very low density lipoproteins pre-beta lipoproteins).





C. high density lipoproteins.

D. chylomicrons.

E. free fatty acids bound to serum albumin.

43. An increase in plasma bilirubin diglucuronide concentrationaccompanied by a marked decrease in fecal urobilinogen content ismost often associated with

A. acute hemolytic anemia.

B. erythropoetic porphyria.

C. parenchymal liver disease (viral hepatitis).

D. iron deficiency.

E. bile duct obstruction.

44. All of the following compounds are required for purine ringbiosynthesis EXCEPT which one?

A. N10-formyltetrahydrofolate

B. Glutamine

C. Glycine

D. N5-Methyltetrahydrofolate

E. Carbon dioxide

45. A nucleotide intermediate common to the synthesis of all thepyrimidine mononucleotides is

A. CMP.

B. UMP.





C. TMP.

D. UTP.

E. UDP.

46. Hydrolysis of cGMP in the retina involves all of the followingEXCEPT

A. transducin.

B. phosphodiesterase.

C. rhodopsin.

D. guanylate cyclase.

E. light.

47. Which one of the following compounds is a COMMONintermediate in the beta-oxidation of fatty acids, ketogenesis andcholesterogenesis?

A. mevalonic acid

B. acetoacetic acid

C. acetoacetyl-CoA

D. beta-hydroxy-beta-methylglutaryl-CoA

E. malonyl-CoA

48. All of the following statements about integral membrane proteinsare true EXCEPT

A. they are associated with lipid in the membrane.

B. they can be transmembranous.





C. they are amphipathic.

D. they are symmetrically distributed within the membrane.

E. they are only removed from the membrane by drastic treatments.

49. Adipose tissue lacks which one of the following enzymes?

A. glucose 6-phosphate dehydrogenase

B. hormone-sensitive lipase

C. glyceraldehyde 3-phosphate dehydrogenase

D. glycerol kinase

E. glycerol phosphate dehydrogenase

50. The correct structure for palmitic acid is

A. CH3(CH2)12COOH

B. CH3(CH2)14COOH

C. CH3(CH2)16COOH

D. CH3(CH2)18COOH

E. None of the above.

51. The rate-limiting step of fatty acid synthesis is catalyzed by

A. pyruvate dehydrogenase.

B. citrate-cleavage enzyme.

C. malic enzyme.





D. acetyl-CoA carboxylase.

E. thiolase.

52. A high insulin/glucagon ratio indicates

A. early starvation or a low carbohydrate diet.

B. energy storage and protein anabolism.

C. mobilization of fatty acids and protein catabolism.

D. uncontrolled diabetes.

E. prolonged starvation.

53. Phosphoadenosine phosphosulfate (PAPS) participates in the

A. biosynthesis of proteoglycans.

B. synthesis of glutathione.

C. synthesis of cysteine from methionine.

D. conversion of cysteine to homocysteine.

E. phosphorylation of glycerol.

54. An amino acid which is both ketogenic and glucogenic is

A. tyrosine.

B. alanine.

C. leucine.

D. glutamate.

E. histidine.





55. Diacylglycerol

A. activates protein kinase C

B. activates calmodulin dependent reactions

C. causes the rapid release of intracellular calcium

D. inhibits a membrane-bound ATPase

56. Which one of the following enzymes is involved in the mobilizationof fatty acids from triglycerides stored in adipose tissue?

A. pancreatic lipase

B. lipoprotein lipase

C. hormone-sensitive lipase

D. phospholipase C

E. carnitine acyltransferase

57. Which of the following is the primary end product of de novo fattyacid synthesis in mammalian liver?

A. oleate

B. vitamin A

C. linoleate

D. propionate

E. palmitate

58. Acyl carrier protein is involved in





A. beta oxidation.

B. cholesterol biosynthesis.

C. fatty acid transport.

D. fatty acid biosynthesis.

E. prostaglandin synthesis.

59. Which of the following statements concerning striated muscle istrue?

A. Both thick and thin filaments shorten during contractions.

B. Calcium is actively concentrated in the sarcoplasmic

reticulum during relaxation.

C. Myosin filaments are anchored at the Z line.

D. Creatine phosphate hydrolysis is the primary source of energy.

E. Actin-tropomyosin complexes catalyze ATP hydrolysis.

60. Which amino acid is converted by transamination into oxaloaceticacid?

A. Lysine

B. Aspartic

C. Glutamic

D. Threonine

E. Methionine

61. Hyaluronic acid consists of repeating units of





A. glucose and fructose.

B. glucuronic acid and N-acetylglucosamine.

C. galactose and N-acetylgalactosamine.

D. glucuronic acid and N-acetylgalactosamine.

E. glucuronic acid and galactose.

62. Which urea cycle intermediate is synthesized in the mitochondria?

A. Arginine

B. Citrulline

C. Ornithine

D. Argininosuccinate

63. Which of the following is the primary defect in familialhypercholesterolemia?

A. LDL apoproteins are missing.

B. HDL apoproteins are missing.

C. LDL receptors are deficient.

D. Lipoprotein lipase is deficient.

E. HMG-CoA reductase is missing or defective

64. The regulated step in porphyrin biosynthesis is the step catalyzedby

A. delta-amino levulinic acid synthase.

B. uroporphyrinogen III cosynthase.





C. porphobilinogen deaminase.

D. protoporphyrin IX isomerase.

E. ferrochelatase.

65. The rate-limiting step in the conversion of cholesterol to bile acidsis

A. side chain oxidation.

B. 12-alpha-hydroxylation.

C. 7-alpha-hydroxylation.

D. 25-alpha hydroxylation.

E. aromatization of the A ring.

66. Pancreatic lipase acts on triacylglycerols to cleave

A. only the fatty acid residue at position 2.

B. the fatty acid residues at positions 2 and 3.

C. the fatty acid residues at positions 1 and 3.

D. only the fatty acid residue at position 1.

E. the fatty acid residues at positions 1 and 2.

67. Actin is released from its interaction with myosin by the additionof

A. ADP

B. magnesium ions

C. inorganic phosphate





D. ATP

E. calcium ions

68. Iron is transported in blood almost entirely as

A. free ferric ion.

B. ferritin.

C. free ferrous ion.

D. transferrin.

E. hemosiderin.

69. Acetyl-CoA for de novo fatty acid biosynthesis is formed by thecytoplasmic cleavage of

A. pyruvate

B. oxaloacetate

C. citrate

D. alpha-ketoglutarate

E. acetoacetate

70. All of the molecules below are nucleosides EXCEPT which one?

A. adenosine

B. uridine

C. cytosine

D. guanosine

E. inosine





71. The metabolite of vitamin D3 which is MOST ACTIVE ininitiating the sequence of events in intestinal mucosal cells that resultin an increased uptake of dietary calcium is

A. 25-hydroxycholecalciferol.

B. 1,25-dihydroxycholecalciferol.

C. 7-dehydrocholesterol.

D. cholecalciferol.

E. ergocalciferol.

72. All of the following statements about a facilitated diffusiontransport system are correct EXCEPT

A. Like an enzyme, the transporter would display saturation orMichaelis-Menten kinetics.

B. Transport of a compound would be expected to be inhibited by aclose chemical analogue.

C. Transport would be possible in only one direction.

D. The transporter would be expected to have specificity, i.e., it wouldbe expected to transport only one or a few closely-related compounds.

E. A mutation, resulting in the loss of ability to make a transporter,could result in loss of ability of a cell to take up a given compound.

73. All of the following are true of mixed micelles formed in theintestine EXCEPT which one?

A. They provide a vehicle for the absorption of fat soluble vitamins.

B. They are absorbed directly into the lymphatic system via thelacteals.





C. They contain cholesterol.

D. They contain free fatty acids.

E. The non-polar ends of lipids are oriented toward the center of themicelles.

74. The committed step in purine nucleotide biosynthesis involves

A. the formation of PRPP.

B. the formation of 5-phosphoribosylamine.

C. ring closure to yield IMP.

D. conversion of folic acid to tetrahydrofolic acid.

E. the formation of orotic acid.

75. In the fed state

A. glucose is converted to glycogen and stored in the muscle.

B. adipose tissue converts triglycerides to glucose.

C. the alanine cycle transports nitrogen from muscle to the liver.

D. glycogen synthase in liver is phosphorylated.

E. glycogen phosphorylase is in the active form.

Answer Key:

1.B 11.B 21.E 31.D 41.A 51.D 61.B 71.B

2.B 12.D 22.C 32.C 42.E 52.B 62.B 72.C





Liaison Decisions

Question 4 Discard and add 1 point to the raw score of those students whoanswered C

Question 12 Discard and add 1 point to the raw score of those studentswho answered D

Question 23 Discard and add 1 point to the raw score of those studentswho answered B

Question 32 Accept A or C

Question 34 Accept B or C

Question 36 Discard and add 1 point to the raw score of those studentswho answered A

Question 43 Accept C or E

3.B 13.D 23.B 33.D 43.E 53.A 63.C 73.B

4.C 14.E 24.C 34.B 44.D 54.A 64.A 74.B

5.A 15.A 25.A 35.B 45.B 55.A 65.C 75.A

6.B 16.A 26.C 36.A 46.D 56.C 66.C

7.C 17.C 27.E 37.C 47.C 57.E 67.D

8.E 18.C 28.B 38.A 48.D 58.D 68.D

9.C 19.B 29.D 39.A 49.D 59.B 69.C

10.D 20.D 30.B 40.A 50.B 60.B 70.C





Question 45 Accept B or E

Question 58 Accept C or D

Question 70 Discard and add 1 point to the raw score of those studentswho answered C

Question 72 Discard and add 1 point to the raw score of those studentswho answered C

Question 73 Accept B or C

Copyright © 1998 Department of Cell Biology & Biochemistry, TTUHSC

Last revised 11/30/99





medbiochem home medbiochem exam 2, 1998 · pdf filemedbiochem home course description lecture...

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