(200 points) Each of the following statements is followed by five suggested answers or completions. On the answer sheet, mark the one which is best in each case.
1. Pyridoxal phosphate acts as coenzyme in most A. transmethylation reactions. B. carbon dioxide fixation reactions. C. transamination reactions. D. kinase reactions. E. none of the above.
2. At their isoelectric point proteins have
A. no ionized groups.
B. no positively charged groups.
C. no negatively charged groups.
D. equal numbers of positively and negatively charged groups.
E. none of the above
3. Which statement about the mammalian -ketoglutarate dehydrogenase complex is FALSE?
A. It consists of an aggregate containing three different enzyme activities and five different cofactors.
B. The only cofactor undergoing a net change during the overall reaction is FAD --> FADH2.
C. Lipoic acid is alternately oxidized and reduced as catalysis continues.
D. Lipoic acid is covalently attached to one of the proteins in the complex.
E. The first step catalyzed is the formation of hydroxyethyl- thiamine pyrophosphate and the release of carbon dioxide.
4. Allopurinol lowers blood urate levels by
A. blocking tubular reabsorption of uric acid.
B. inhibiting hypoxanthine-guanine phosphoribosyl transferase.
C. increasing uptake of sodium urate by leukocytes.
D. inhibiting the conversion of hypoxanthine to xanthine.
E. activating urate oxidase.
5. In the regulation of an overall metabolic sequence, which of the following reactions is most likely to be modulated by allosteric effectors?
A. All steps have equal probability to be regulated
B. The last reaction of the sequence.
C. The initial committed step of the sequence.
D. The fastest reaction of the sequence.
E. A reaction with an overall equilibrium constant of one
6. All of the following are true concerning fibrin EXCEPT:
A. it is formed during primary hemostasis
B. it is formed from fibrinogen by specific cleavage by thrombin.
C. it does not have intrinsic protease activity
D. it becomes covalently crosslinked to stabilize a clot
E. it is normally degraded by plasmin
7. A patient first experienced chest pains approximately 6 hr ago. A good diagnostic test for the possibility of a myocardial infarction would be:
A. an immunoassay quantitating troponin levels in the serum
B. an electrophoretic assay to determine the relative serum levels of LDH isozymes
C. an electrophoretic assay to determine the relative serum levels of creatine kinase isozymes
D. A, B, C are all correct
E. A and C are correct
8. In proteins, the side chain of serine can be involved in all of the following EXCEPT:
A. phosphorylation
B. hydrogen bonding
C. covalent carbohydrate attachment
D. ionic interactions
9. All of the following statements about integral membrane proteins are true EXCEPT
A. they are associated with lipid in the membrane.
B. they often span the membrane with an helical segment
C. they often act as receptors for hormones and growth factors.
D. they are symmetrically distributed within the membrane.
E. they are only removed from the membrane by drastic treatments,
such as with a detergent.
10. All of the following enzymes carry out substrate level phosphorylations EXCEPT
A. ATP synthase
B. phosphoglycerate kinase
C. pyruvate kinase
D. succinyl CoA synthetase
11. The signal peptide found at the amino end of proteins destined to be secreted from eukaryotic cells:
A. consists largely of hydrophobic amino acids.
B. is added to the polypeptide chain post-translationally.
C. is cleaved off prior to SRP docking at the RER
D. consists largely of hydrophilic amino acids.
E. consists of an amphipathic helix
12. Which of the following components of the mitochondrial electron transport system are incapable of carrying 2 electrons?
1. Ubiquinone
2. cytochrome C
3. FMN
4. Heme b
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
13. The major pathway by which mature adult red cells generate ATP is:
A. aerobic metabolism.
B. anaerobic glycolysis.
C. hexose monophosphate shunt activity.
D. generation of 2,3-diphosphoglycerate.
E. fatty acid oxidation.
14. Intermediates or reactants in urea formation include:
1. argininosuccinate.
2. carbamoyl phosphate.
3. bicarbonate.
4. arginine.
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
15. Dihydroxyacetone phosphate serves all of the following purposes in mammalian cells EXCEPT:
A. as part of a shuttle system for transporting electrons from
NADH to the mitochondria.
B. as precursor of the "glycerol" moiety of glycerides.
C. as precursor of glyceraldehyde 3-phosphate.
D. as precursor of fructose 1,6-bisphosphate.
E. as precursor of leucine.
16. The absorption of glucose from the intestinal lumen into mucosal cells:
A. does not require a carrier protein.
B. requires bile salts
C. occurs down a glucose concentration gradient.
D. requires a greater concentration of sodium outside the cell than inside the cell.
E. occurs through an insulin-responsive glucose transporter
17. All of the following statements about allosteric enzymes are generally correct EXCEPT which one?
A. They exhibit cooperativity in the binding of substrate.
B. The affinity of an enzyme for its substrate is decreased by a
positive allosteric modulator.
C. Some contain regulatory subunits which do not bind substrate.
D. They are commonly involved in the control of metabolic pathways
by feedback inhibition.
E. They give sigmoid kinetics (v vs S graphs).
18. Fatty acid synthase:
1. is a dimer of identical subunits having multiple enzymatic functions
2. cannot make stearate
3. requires NADPH and a covalently bound cofactor that is similar to CoA
4. is found in the cytosolic compartment
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2 and 3
E. all are correct
19. Which of the following enzymes are unique to gluconeogenesis (as opposed to glycolysis)?
1. glucose 6-phosphatase
2. pyruvate kinase
3. PEP carboxykinase
4. aldolase
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
20. Diphtheria toxin is a potent inhibitor of protein synthesis. Which one of the following statements closely describes its mode of action?
A. It inhibits the binding of N-formyl methionine-tRNA to 30S subunit of ribosomes.
B. It inhibits the peptidyl transferase activity of the large subunit of ribosomes.
C. It catalyzes the transfer of adenosine diphosphate ribosyl moiety of NAD to the elongation factor EF-2 (translocase).
D. It causes premature chain termination by covalent attachment of the toxin molecule to the growing polypeptide chain.
E. It inhibits RNA polymerase I.
21. A newly discovered inhibitor was found to cause the accumulation of FMNH2, reduced ubiquinone, and oxidized cytochrome C. It is most likely to be
A. an uncoupler of oxidative phosphorylation
B. affecting a component of complex I
C. affecting a component of complex II
D. affecting a component of complex III
E. affecting a component of complex IV
22. Which of the following amino acids is oxidatively deaminated to furnish ammonium ion for the urea cycle?
A. Tryptophan
B. Glutamate
C. Arginine
D. Glutathione
23. A general mechanism of action of steroid hormones involves:
A. binding of the steroid hormone to a cytoplasmic or nuclear receptor protein.
B. stimulation of plasma membrane-bound adenylate cyclase.
C. activation of a protein kinase signalling cascade.
D. binding of the steroid hormone to a transmembrane receptor of target cells.
E. activation of a specific phospholipase
24. The major site of cholesterol biosynthesis in the human is
A. intestinal epithelia
B. gall bladder
C. pancreas
D. adrenal gland
E. liver
25. Phenylketonuria is a genetic defect due to the absence of the enzyme:
A. alpha-keto acid decarboxylase.
B. tyrosinase.
C. homogentisate oxidase.
D. alanine transaminase.
E. phenylalanine hydroxylase.
26. In biological systems, which compound mediates transfer reactions involving the "one-carbon" pool in multiple oxidation states?
A. glutathione.
B. pyridoxal phosphate.
C. tetrahydrofolic acid.
D. vitamin K.
E. biotin.
27. Which of the following is not true concerning reduction of ribonucleotides?
A. ribonucleoside diphosphates are the substrates that are reduced by ribonucleotide reductase
B. NADPH provides the reducing power for synthesis of deoxyribonucleotides
C. each of the four ribonucleotides are reduced by a separate isozyme of ribonucleotide reductase
D. two proteins, thioredoxin and thioredoxin reductase, are necessary to maintain ribonucleotide reductase in its active reduced state
E. the mechanism of ribonucleotide reductase involves an unusual tyrosine free radical
28. Glycogen synthase and glycogen phosphorylase are both _________ proteins in their _________ state. (fill in the blanks)
A. phosphorylated, inactive
B. sulfated, active
C. pyrophosphorylated, active
D. phosphorylated, active
E. none of the above
29. Which of the following enzymes are involved in the EXCISION-REPAIR of UV-induced pyrimidine dimers?
1. an endonuclease
2. DNA ligase
3. DNA polymerase I
4. photoreactivatingenzyme (DNA photolyase)
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
30. Fatty acids from adipose tissue are transported to sites of utilization in the form of:
A. triglycerides bound to serum albumin.
B. very low density lipoproteins.
C. high density lipoproteins.
D. chylomicrons.
E. free fatty acids bound to serum albumin.
31. Which of the following enzymes catalyzes the committed and rate-limiting step of cholesterol synthesis from acetyl-CoA?
A. acetyl CoA carboxylase
B. citrate lyase
C. HMG CoA reductase
D. thiolase
E. mevalonate kinase
32. Restriction endonucleases:
A. digest DNA duplex molecules from the 5'-OH ends.
B. attack only single stranded DNA.
C. have nucleotide sequence specificity.
D. randomly digest double stranded DNA molecules.
E. are not produced by bacteria.
33. The absorption of which of the following might be lowered by treatment for high cholesterol levels with bile acid sequestrants such as cholestyramine?
1. triglycerides
2. vitamin E
3. vitamin A
4. vitamin K
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2 and 3
E. all of them
34. Which statement about the Cori cycle is TRUE?
A. All of the component reactions occur in the liver.
B. Lactate from muscle is used in the liver as a gluconeogenic substrate.
C. Free glucose, produced from glycogen in skeletal muscle, is utilized for the synthesis of glycogen in the liver.
D. It is the cycle in the liver by which glycogen is synthesized from and degraded to glucose 1-phosphate.
E. All of the component reactions occur in skeletal muscle.
35. The citric acid cycle is initiated by the condensation of two molecules, which are:
A. NAD and oxaloacetate.
B. pyruvate and malate.
C. NAD and oxalosuccinate.
D. acetyl-CoA and oxaloacetate.
E. acetyl-CoA and oxalosuccinate.
36. Which of the groups below contains two compounds that are parts of coenzymes involved in the beta-oxidation of fatty acids?
A. Vitamin D and pantothenic acid
B. Biotin and folic acid
C. Niacin and riboflavin
D. Pyridoxine and thiamine
E. Choline and carnitine
37. Which of the following repair processes occur only in cells that are actively replicating their DNA?
1. excision repair
2. mismatch repair
3. photoreactivation
4. recombinational repair
A. 1 only
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
38. The main function of the glycerol phosphate shuttle is in
A. anaerobic glycolysis for regeneration of NAD.
B. the -oxidation of fatty acids.
C. the transport of reducing equivalents into mitochondria from
NADH formed during glycolysis.
D. the biosynthesis of triacylglycerols.
E. the biosynthesis of serine for use in mitochondrial protein synthesis.
39. An anticodon is:
A. the part of a DNA molecule which codes for chain termination.
B. a 3-nucleotide sequence of a mRNA molecule.
C. a specific part of a tRNA molecule.
D. a nucleotide triplet of a rRNA molecule.
E. the portion of a ribosomal subunit which interacts with aminoacyl-tRNA synthetase.
40. In the liver, increased cyclic AMP leads to increases in the activity of all the following enzymes EXCEPT
A. glycogen phosphorylase.
B. fructose 2,6 bisphosphatase.
C. pyruvate kinase.
D. phosphorylase kinase.
E. cyclic AMP-dependent protein kinase.
41. All of the following molecules, without further metabolism, can cross the inner membrane of functioning mitochondria EXCEPT
A. ATP.
B. oxygen.
C. inorganic phosphate.
D. pyruvate.
E. acetyl CoA.
42. Since the cloning of the HD (Huntington's Disease) gene and identification of the specific defect, a genetic screen can be utilized that does not depend on access to samples from other family members. This screen utilizes which of the following methods:
A. RFLP analysis
B. DNA sequencing
C. Southern blotting with an ASO (allele specific oligonucleotide) probe
D. SSC (single strand conformational analysis)
E. PCR (polymerase chain reaction)
43. The normal storage form of iron in tissues is:
A. an iron-transferrin complex.
B. ferritin.
C. hemoglobin.
D. hemosiderin.
E. None of the above. Iron is not stored; it must be supplied daily
in the diet.
44. The function of the enzyme acetylcholine esterase is to
A. concentrate acetylcholine in synaptic vesicles by exchanging it for protons
B. to signal the release of acetylcholine into the synaptic cleft
C. to clear acetylcholine after it has been secreted into the synaptic cleft
D. to synthesize acetylcholine from acetylCoA and choline
E. to bind to receptors on the postsynaptic membrane
45. Which tissue normally has the highest concentration (per gram of tissue) of glycogen?
A. adipose tissue
B. brain
C. liver
D. red blood cell
E. skeletal muscle
46. Which enzyme of the Krebs cycle is most similar to pyruvate dehydrogenase?
A. citrate synthase
B. succinyl-CoA synthetase
C. succinic dehydrogenase
D. -ketoglutarate dehydrogenase
E. isocitrate dehydrogenase
47. Glutamate can be formed directly (one step) from which citric acid cycle intermediate?
A. malic acid
B. succinic acid
C. alpha-ketoglutarate
D. oxaloacetate
E. fumaric acid
48. An important drug which functions by releasing NO leading to relaxation of heart muscle and vasodilation is:
A. lithium
B. theophylline
C. ibuprofin
D. nitroglycerine
E. l-dopa
49. Which of the following is not one of the important criteria that is considered in determining if a genetic disease is a good candidate for gene therapy?
A. the gene defect must be known and the normal gene must be cloned and characterized
B. the disease should be life threatening with no adequate therapy
C. optimally the genetic defect should be due to a dominant mutation
D. the target tissue should be easily accessible
E. it should exhibit a nonpleiotropic phenotype and should be encoded by a single copy gene
50. Excess circulating cholesterol (as LDL) can cause health problems but cholesterol is an essential compound. Positive functions of cholesterol (or 7-dehydrocholesterol) include:
1. it is a structural component of plasma membranes
2. it is a precursor of vitamin D
3. it is a precursor of bile salts
4. it is a precursor of steroid hormones
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
51. Aspirin would have the greatest effect on the synthesis of which of the following compounds?
A. leukotriene B
B. arachidonic acid
C. progesterone
D. prostaglandin A2
E. diacylglycerol
52. The anticancer drug tamoxifen functions by
A. inhibiting topoisomerase II
B. alkylating DNA in rapidly growing cells
C. stabilizing microtubules preventing mitosis
D. binding to and blocking estrogen receptor function
E. blocking DNA synthesis by inhibiting thymidylate synthase
53. Which of the following is not an important factor in the activation of a growth factor receptor tyrosine kinase?
A. ligand (growth factor) binding
B. receptor dimerization
C. receptor/G protein interaction
D. autophosphorylation (cross-phosphorylation)
54. Each of the following statements is correct EXCEPT which one?
A. Heme is the prosthetic group of myoglobin and certain cytochromes.
B. The ring structure of heme is composed of four pyrrole rings
linked by one-carbon bridges.
C. In hemoglobin, one of the coordinate linkages of each iron atom is to a histidine nitrogen.
D. The phenomenon of cooperativity is observed in the binding of oxygen to myoglobin.
E. The binding of 2,3-BPG to Hb decreases its affinity for oxygen.
55. What vitamin is needed by the liver cell for the synthesis of the plasma protein prothrombin?
A. vitamin D.
B. vitamin E.
C. vitamin K.
D. vitamin A.
E. vitamin B12.
56. A molecule produced both in the Krebs cycle and the urea cycle is
A. arginine.
B. aspartate.
C. ornithine.
D. fumarate.
E. citrate.
57. Allosteric control of enzyme action requires
A. a cofactor derived from a vitamin.
B. a metal ion.
C. the conversion of one form of the enzyme to another by the action of proteolytic enzymes.
D. a conformational change in an enzyme that changes its catalytic activity.
E. an effector that is the product of the enzymatic reaction and which competes for the active site of the enzyme.
58. All of the following statements are correct EXCEPT which one?
A. During RNA synthesis, RNA polymerase moves along the DNA template strand in the 3' --> 5' direction thereby catalyzing RNA chain growth in the 5' -> 3' direction.
B. Binding of each successive aminoacyl-tRNA to the aminoacyl (A) site on the ribosome requires participation of an elongation factor and expenditure of a high energy phosphate from GTP.
C. The site of attachment of the amino acid in aminoacyl transfer RNA is the 3' position of the ribose of the terminal adenosine.
D. Termination of protein synthesis at a stop codon is promoted by a protein, which is bound to the ribosome at the A site.
E. The amino acid sequence of a protein is determined during synthesis by direct interactions between amino acids and codons in the mRNA template.
59. The protein involved in separating the DNA strands at a DNA replication fork is called:
A. helicase.
B. DNA polymerase I.
C. DNA polymerase III.
D. primase.
E. DNA gyrase.
60. A number of genetic diseases are a result of abnormal mRNA splicing. All of the following are involved in splicing EXCEPT:
A. 5' splicing signal
B. 3' splicing signal
C. 5' TATA box
D. U snRNPs
E. branch point consensus signal
61. An enzyme present in the liver but NOT in muscle is
A. hexokinase.
B. glucose 6-phosphatase.
C. lactate dehydrogenase.
D. pyruvate dehydrogenase.
E. glycogen phosphorylase.
62. All of the following compounds are carbon sources for the net synthesis of glucose in liver EXCEPT
A. lactate.
B. Beta-hydroxybutyrate.
C. alanine.
D. aspartate.
E. glycerol.
63. Regarding the process of DNA replication in E. coli which of the following statements is INCORRECT?
A. DNA replication is a semiconservative process.
B. There is a unique site at which replication is initiated.
C. DNA replication is unidirectional.
D. The mechanism of replication is such that there is a leading strand and a lagging strand at each replicating fork.
E. DNA synthesis occurs in the 5' to 3' direction.
64. In untreated insulin-dependent diabetes, all these differences from the normal state are observed EXCEPT
A. transport of glucose into adipose tissue is increased.
B. gluconeogenesis is increased.
C. glycogen breakdown in liver is increased.
D. lipolysis in adipose tissue is increased.
E. ketogenesis is increased.
65. An enzyme affects the rate of a chemical reaction by:
A. decreasing the free energy of the reaction.
B. increasing the free energy of the reaction.
C. lowering the energy of activation of the reaction.
D. raising the energy of activation of the reaction.
E. displacing the equilibrium constant.
66. For transport across the inner mitochondrial membrane, long chain fatty acids are attached to
A. coenzyme A.
B. acyl transacylase.
C. phosphatidylethanolamine.
D. acyl transferase.
E. carnitine.
67. Defective collagen in scurvy is due to insufficient vitamin C which
A. is ordinarily incorporated into crosslinks between collagen molecules.
B. is usually involved in the hydroxylation of prolyl residues.
C. inhibits the oxidative degradation of collagen.
D. is required for the conversion of lysyl residues into aldehydes.
E. is needed to trap free radicals
68. The sequence shown below is one strand of a double-stranded DNA fragment. Which of the oligonucleotide pairs given below could be used to amplify the entire sequence shown by PCR.
5'-TGCCCAGGCCATGGAACACCAGCTCCTGTGCTGCGAATAAGAAACCATCCGAACG-3'
A. 5'-TGCCCAGGCCAT-3' and 5'-CCATCCGAACG-3'
B. 5'-ATGGCCTGGGCA-3' and 5'-CGTTCGGATGG-3'
C. 5'-ACGGGTCCGGTA-3' and 5'-GCAAGCCTACC-3'
D. 5'-TGCCCAGGCCAT-3' and 5'-CGTTCGGATGG-3'
E. 5'-ATGGCCTGGGCA-3' and 5'-CCATCCGAACG-3'
69. Carbon monoxide would be expected to interfere with the function of
A. myosin and myoglobin.
B. myoglobin and cytochrome oxidase.
C. cytochrome oxidase and lactate dehydrogenase.
D. lactate dehydrogenase and myosin.
E. myosin and cytochrome oxidase.
70. In the red blood cells, NADPH is required
1. for the maintenance of reduced glutathione.
2. as a source of electrons for oxidative phosphorylation.
3. for the formation of ribose 5-phosphate from glucose.
4. as a reactant in the pentose phosphate pathway.
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
71. Mobilization of fat from adipose tissue requires the enzymatic activity of:
A. lipoprotein lipase.
B. hormone-sensitive lipase.
C. phospholipase A2.
D. pancreatic lipase.
E. glycerol kinase.
72. All of the following enzymes would be active in catalyzing protein hydrolysis in the intestine EXCEPT which one?
A. trypsin.
B. pepsin.
C. chymotrypsin.
D. carboxypeptidase A.
E. all of the above are active.
73. All of the following are true concerning the promoter region of a gene EXCEPT
A. it insures that transcription begins at the proper place
B. it can bind specifically with certain proteins to enhance
transcription.
C. it can participate as part of control mechanisms to coordinate
transcription with the needs of the cell.
D. it is transcribed in its entirety.
74. Which of the following statements is not true concerning synthesis of glucose from lactate?
A. The process is not the simple reversal of glycolysis.
B. Some of the necessary enzymes are in the cytoplasm and
some in mitochondria.
C. The first enzyme required is lactate dehydrogenase
D. It occurs primarily in skeletal muscle.
E. oxaloacetate is an intermediate in the process
75. With respect to plasma lipoproteins:
1. high density lipoproteins have the highest apolipoprotein content.
2. very low density lipoproteins transport lipid from liver to other tissues.
3. some apolipoproteins are found in several types of lipoprotein particles
4. receptors for LDL are found only in the liver
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
76. Many carbon dioxide utilizing enzymes such as pyruvate carboxylase use as a coenzyme the vitamin:
A. biotin.
B. thiamine.
C. pyridoxine.
D. riboflavin.
E. niacin.
77. Bilirubin:
A. is mainly derived from the rapid turnover of heme-containing enzymes in the liver.
B. is formed by oxidation of heme, initially to biliverdin.
C. is mainly found free in the blood.
D. is tightly bound to serum albumin only after it is conjugated.
E. None of the above.
78. When a template strand of DNA with the sequence AGTCAG (5' -> 3') is transcribed by RNA polymerase the resulting RNA would have the sequence (5' -> 3'):
A. TCAGTC
B. UCAGUC
C. CUGACU
D. CTGACT
E. AGUCAG
79. All of the following statements concerning the first amino acid to be incorporated into a protein during translation in a mammalian cell are true EXCEPT:
A. it is generally modified by formylation of its amino group
B. it is generally coded for by an AUG codon near the 5'-end of the messenger RNA.
C. it is "delivered" to the ribosome attached to a special initiator.
D. it is practically always methionine.
E. it is not always found at the amino-terminus of the protein in its final form.
80. In a cancer cell, the involvement of a tumor suppressor gene
A. generally results from a mutation leading to a "gain of function" for the protein encoded by the gene
B. leads to the loss of an inhibitory or checkpoint control of cell growth
C. is generally the result of gene amplification
D. results in the expression of a protein that is normally involved in stimulating cell growth
E. alone can cause tumorigenic transformation
81. Coenzyme A contains the vitamin:
A. pyridoxine.
B. thiamine.
C. riboflavin.
D. pantothenic acid.
E. nicotinic acid.
82. The rate of an enzyme catalyzed reaction
1. can be determined by measuring the increase in product concentration
with respect to time.
2. is independent of the enzyme concentration.
3. at saturating substrate concentrations, becomes zero-order with respect to substrate.
4. shows the same pH dependence for all enzymes.
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
83. Which of the following are positive allosteric effectors of phosphofructokinase-1?
1. ATP
2. fructose 2,6-bisphosphate
3. citrate
4. AMP
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
84. ATP synthase
A. is located outside the inner mitochondrial membrane
B. reduces oxygen to form water
C. is thought to operate by a binding change mechanism in which 3 substrate binding sites are each in a different conformation at any one time
D. is thought function through a ping-pong catalytic mechanism involving sequential binding of ADP and Pi, first to the alpha subunit and then to the beta subunit
E. is able to continuously synthesize ATP even in the absence of a proton motive force
85. During prolonged starvation, the brain oxidizes significant amounts of
1. glucose.
2. fatty acyl carnitine.
3. acetoacetate.
4. free fatty acids.
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
86. Concerning variable regions of immunoglobulins, which of the following is correct?
A. they are involved in binding of antigen.
B. they include the site which is necessary for clearance of antibody/antigen complexes
C. they occur only in the light chain subunits.
D. they occur only in the heavy chain subunits.
E. they are found only in the IgG class of immunoglobulins
87. The construction of a human genomic DNA library in E. coli would involve or require which of the following?
1. a bacteriophage or plasmid vector with a bacterial origin of replication.
2. the preliminary purification of a unique DNA fragment generated
by restriction endonuclease digestion of nuclear DNA
3. a large number of genomic DNA fragments generated by restriction endonuclease digestion of human genomic DNA
4. a bacteriophage or plasmid vector containing multiple cloning site just upstream of a Shine-Dalgarno sequence
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
88. All of the following directly contribute one or more atoms to the synthesis of a purine ring EXCEPT
A. glutamine
B. bicarbonate ion (CO2)
C. glycine
D. arginine
E. aspartate
89. The left-handed helices of a collagen chain is an example of
A. primary structure
B. secondary structure
C. tertiary structure
D. quaternary structure
E. none of the above
90. Reducing equivalents necessary for de novo biosynthesis of fatty acids can be produced directly by the action of
1. glucose 6-phosphate dehydrogenase.
2. malate dehydrogenase.
3. malic enzyme.
4. succinate dehydrogenase.
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
91. Which of the following statements concerning receptors for low density lipoproteins (LDL) is correct?
A. they are synthesized free in the cytosol and then inserted into the plasma membrane sites.
B. the receptor and its ligand are completely degraded within lysosomes following endocytosis.
C. they play a key role in controlling serum cholesterol levels.
D. they can bind high density lipoproteins (HDL) as well as LDL
E. their synthesis is stimulated by high intracellular levels of cholesterol
92. The Na+K+ ATPase transport system
A. is restricted to the plasma membranes of kidney, brain and erythrocytes.
B. will normally transport both Na+ and K+ in either direction across the membrane.
C. is important in maintaining the membrane potential across the plasma membrane
D. is a peripheral protein associated with the extracellular side of the plasma membrane.
E. allows transport of the ions down their concentration gradients
93. DNA polymerases and RNA polymerases both
1. require a template
2. require a primer to initiate synthesis
3. catalyze formation of phosphodiester bonds
4. utilize ATP as a substrate
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
94. All of the following are TRUE concerning sources of energy and glucose during fasting EXCEPT?
A. Alanine is released from skeletal muscle to be used for gluconeogenesis in the liver.
B. Fatty acid oxidation supplies the ATP required for gluconeogenesis.
C. Glycerol is released from adipose tissue to be used for gluconeogenesis in the liver.
D. Excess free fatty acids are converted to ketone bodies which are then used as an energy source by the liver.
95. Physiologically irreversible reactions in glycolysis include those catalyzed by which of the following enzymes:
1. pyruvate kinase.
2. hexokinase.
3. phosphofructokinase.
4. glyceraldehyde 3-phosphate dehydrogenase.
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2, and 3
E. all of them
96. Which of the following is not a true statement?
A. Chaperones chemically modify nascent polypeptide chains in order to assist folding
B. Protein folding is driven primarily by hydrophobic interactions
C. Protein folding occurs step-wise with several intermediates
D. The information required for proper folding of a protein is contained within the primary sequence
E. Certain enzymes aid protein folding by catalyzing otherwise kinetically slow steps
97. Biological oxidation of which of the following provides the most calories of energy per gram?
A. starch
B. fatty acids
C. cholesterol
E. nucleic acids
D. protein
98. Methotrexate interferes with DNA synthesis by blocking which of the following?
A. UDP dUTP
B. dCMP dUMP
C. thioredoxin disulfide thioredoxin sulfhydryls
D. dUMP dTMP
E. relaxed DNA to supercoiled DNA
99. 10 ml of a 0.1 M solution of a weak acid (Ka = 10-6 M) is mixed with an equal volume of a 0.1 M solution of the sodium salt of that acid. The final pH will be approximately:
A. 3
B. 4
C. 5
D. 6
E. insufficient data to determine
100. The absence of which coagulation factor is responsible for classical hemophilia A?
A. Factor II
B. Factor V
C. Factor VII
D. Factor VIII
E. Factor X