Biochemistry review questionProtein metabolism1. One function of the small protein ubiquitin is: A. to recognize abnormal proteins so they can be degraded B. to degrade proteins within the lysosome C. to become covalently linked to proteins to "mark" them for degradation D. to sort endocytosed proteins to the lysosome for degradation E. to add PEST sequences to proteins to promote their turnover 2. All of the following statements are true regarding turnover of proteins in eukaryotic EXCEPT A. the rate of turnover of a protein may be controlled by altering either the rate of its synthesis or its degradation. B. some mammalian proteins have a half-life of less than an hour. C. polyubiquitination is a signal for intracellular degradation. D. the C-terminal amino acid of proteins determines their rate of degradation. E. lysosomal hydrolytic enzymes are extensively involved in intracellular degradation of proteins. 3. What enzyme(s) or enzyme complex is responsible for the degradation of ubiquitinated proteins? A. cathepsins B. zymogens C. proteasome D. ribosome E. chymotrypsinogen 4. The enzyme defect in homocystinuria is A. cysteine synthase. B. cystathionine synthase. C. cystathionase. D. S-adenosylmethionine sulfatase. E. S-adenosylhomocysteine sulfatase. 5. In mammals, which enzyme(s) must act to catalyze the production of ammonium ion most directly from alanine? A. transaminase, glutaminase B. transaminase C. transaminase, glutamate dehydrogenase D. aminopeptidase, glutamae dehydrogenase E. alanine oxidase 6. Most ammonia formation in the kidney is via the enzyme A. urease. B. uricase. C. arginase. D. carbamoyl phosphate synthetase. E. glutaminase.
7. A reaction in mammalian tissues which requires the participation of BOTH folate and vitamin B12 coenzymes is: A. biosynthesis de novo of IMP. B. methylmalonyl CoA mutase. C. conversion of formiminoglutamate (FIGLU) to glutamate. D. methionine synthase (homocysteine methyltransferase). E. cystathionine synthetase. 8. Enzymes that incorporate free ammonia into forms useful for the central pathways of amino acid metabolism include A. aspartate transaminase and alanine transaminase. B. carbamoyl phosphate synthase II and adenosine deaminase. C. alpha-ketoglutarate aminotransferase and phosphoserine transaminase. D. glutamine synthetase and glutamate dehydrogenase. E. phenylalanine hydroxylase and cystathionase. 9. All of the following are essential amino acids EXCEPT: A. lysine B. valine C. threonine D. serine E. tryptophan 10. The amino acid that is involved in almost every aminotransferase reaction is: A. pyruvate B. aspartate C. lysine D. glutamate E. glutamine 11. Protein metabolism differs from that of fat and carbohydrate in that: A. proteins are absorbed directly into the blood without being broken into their constituent amino acids. B. there is no separate storage form of proteins in the body. C. proteins cannot be utilized for energy. D. excess dietary protein is excreted without metabolism. E. no specific enzymes are necessary to hydrolyze proteins; the acidity of the stomach is sufficient. 12. The nitrogens in urea originate MOST DIRECTLY (fewest number of steps) from: A. NH3 and glutamate B. NH3 and glutamine C. alanine and glutamate D. carbamoyl phosphate and aspartate E. free ammonia 13. Pyridoxal phosphate acts as coenzyme in most: A. dehydrogenation reactions. B. carbon dioxide incorporated reactions. C. transamination reactions.
D. kinase reactions. E. none of the above 14. The major nitrogenous component in urine from an adult on an adequate maintenance diet is: A. amino acids. B. creatinine. C. urea. D. uric acid. E. ammonia. 15. The primary function of the urea cycle is A. to convert toxic ammonia to urea which can be excreted B. the turnover of excess arginine C. the production of the citric acid cycle intermediate fumarate D. the synthesis of ornithine for spermidine synthesis E. the synthesis of aspartate 16. The regeneration of methionine from homocysteine A. occurs only in bacteria B. requires a methyl group to be donated by SAM C. requires pyridoxal phosphate as a cofactor D. involves an S-adenosyl intermediate E. requires vitamin B12 and 5-methyltetrahydrofolate 17. Which of following amino acids can be synthesized directly from a citric acid cycle intermediate by a single transamination step? 1. glutamate 2. glutamine 3. aspartate 4. serine A. 1 B. 1 and 3 C. 2 and 4 D. 1, 2 and 3 E. all of them 18. The most common donor of methyl groups in biosynthetic reactions is A. 5-methyltetrahydrofolate B. S-adenosylmethionine (SAM) C. homocysteine D. 5-formiminotetrahydrofolate E. tetrahydrobiopterin 19. The substrates for the enzyme carbamoyl phosphate synthetase I include: 1. ATP 2. bicarbonate 3. NH3 4. glutamine A. 1 B. 1 and 3
C. 2 and 4 D. 1, 2, and 3 E. all of them 20. Which is not correct about the alanine-glucose cycle A. involves transamination of branched-chain amino acids in muscle. B. serves to carry nitrogen from extrahepatic tissues to the liver. C. supplies glucose to extrahepatic tissues. D. forms free ammonia which enters the bloodstream. 21. Amino groups derived from amino acid catabolism in the muscle are released from the cell predominantly as 1. urea 2. alanine 3. asparagine 4. glutamine A. 1 B. 1 and 3 C. 2 and 4 D. 1, 2, and 3 E. all of them 22. All of the following compounds EXCEPT which one would be expected to be found in excess amounts in the urine in phenylketonuria? A. o-hydroxyphenylacetic acid B. phenyllactic acid C. tyrosine D. phenylacetic acid 23. The utilization of ammonia for synthesis of the alpha-amino group of non-essential amino acids is A. dependent upon the action of glutamate dehydrogenase. B. achieved by reversal of the urea cycle. C. mediated by carbamoyl phosphate. D. effected through the intermediate of carbamino acids. E. dependent upon the intestinal bacterial flora. 24. Liver is the major site for all of the following processes EXCEPT A. transamination of branched chain amino acids. B. synthesis of urea. C. synthesis of glucose from alanine. D. synthesis of ketone bodies. E. phosphorylation of glycerol. 25. The following mammalian enzymes react(s) with substrate ammoniaEXCEPT A. L-glutamate dehydrogenases B. AMP deaminase C. Glutaminase
Answer: 1. C 2. D 3.C 4.B 5.C 6.E 7.D 8.D 9.D 10.D 11. B 12.D 13.C 14.C 15.A 16.E 17.B 18.B 19.D 20.D 21.C 22.C 23.A 24.A 25.D
Biochemistry review question(From nucleotide metabolism to protein biosythesis) Part 1 Each of the following statements is followed by five suggested answers or completions. Mark the one which is best in each case.1.The principal nitrogenous urinary excretion product in humans resulting from the catabolism of AMP is A. creatinine B. urea C. uric acid D. NH4+ E. thymine 2.Phosphoribosyl pyrophosphate A.is required for both purine and pyrimidine synthesis. B.is a ribonucleotide. C.is synthesized from AMP and ribose. D.is a substrate for the first step of UMP biosynthesis. E.synthesis is blocked by aminopterin. 3.An enzyme system, isolated from the liver, converts deoxyuridine-5'-phosphate (dUMP) to thymidine-5'-phosphate ((d)TMP). Which of the following participates in this reaction? A. 5,10-methylene tetrahydrofolic acid B. ATP C. S-adenosylmethionine D. Vitamin B12 E. thioredoxin 4.In an animal fed aminopterin or methotrexate which of the following reactions would you expect to be DIRECTLY impaired? A.The conversion of ribose 5-phosphate to PRPP. B.The formation of IMP from PRPP. C.The formation of GMP from IMP. D.The synthesis of AMP from IMP. E.The formation of UMP from carbamoyl phosphate. 5.All of the carbon and nitrogen atoms of the pyrimidine ring are supplied by which of the groups of compounds listed below? A.glutamate, glycine B.glycine, aspartate C.glutamine, N-10 formyl tetrahydrofolate D.carbamoyl phosphate, ammonia E.carbamoyl phosphate, aspartate 6.GOUT is often treated with A. allopurinol. B. lovastatin. C. sulfa drugs. D. 5-fluorouracil. E. medium chain length fatty acids.
7.In mammalian cells the nitrogen atoms of the purine ring are derived directly from A.aspartate, glutamine and glycine. B.ammonia, glutamine and aspartate. C.urea and ammonia. D.glycine, ammonia and glutamate. E.glycine and aspartate. 8.Carbamoyl phosphate is a key substance in A.purine biosynthesis. B.pyrimidine biosynthesis. C.urea biosynthesis. D.A and B. E.B and C. 9.In the biosynthesis of purines the last common intermediate on the pathway to AMP and GMP is: A.PRPP. B.IMP.C.Phosphoribosylamine. D.AMP. E.xanthosine monophosphate. 10.Which compound is an immediate contributor of three carbon atoms to the de novo biosynthesis of the ring system of uracil? A.aspartate B.glutamate C.5-methyltetrahydrofolate D.glycine E.carbamoyl phosphate 11.The first committed, essentially irreversible step in purine nucleotide biosynthesis is the formation of A.5-phosphoribosylamine. B. formylglycinamide ribotide. C. dihydroorotic acid. D. phosphoribosylpyrophosphate. E. 5-formamidoimidazole-4-carboxamide ribotide. 12.The initial step in the biosynthesis of both pyrimidines and urea involves the formation of A. carbamoyl phosphate B. argininosuccinate C. orotic acid D. ornithine E. carbamoyl aspartate 13.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 14.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 15.DNA excision repair A.involves only two