Biochemistry review question
（Protein metabolism）1. 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 to produce free
ammonia，EXCEPT
A. L-glutamate dehydrogenases
B. AMP deaminase
C. Glutaminase
D. Glutamate-oxaloacetate transaminase
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 distinct steps. B.requires visible light for activation.
C.replaces both strands of a segment of DNA.
D.is deficient in xeroderma pigmentosum. E.is blocked by allopurinol.
16.Which one of the following enzymes catalyzes the elimination of nicks or discontinuities in
DNA that occur during DNA repair or in the linking together of Okazaki fragments?
A. AP exonuclease B. DNA gyrase C. DNA ligase
D. topoisomerase I E. topoisomerase II
17.Semiconservative replication of DNA means that after two rounds of replication
A.only one of the two parental strands is preserved intact in the progeny molecules of DNA.
B.both parental strands remain intact in one of the progeny molecules of DNA.
C.the two parental strands remain intact in different progeny molecules.
D.one of the parental strands is broken down and dispersed in one of the progeny molecules
of DNA, the other parental strand remains intact in one of the progeny molecules.
E.neither of the parental strands appears in the progeny molecules of DNA.
18.The complementary sequence for 5'-TCTAAG-3' is
A. 5'-AGATTC-3' B. 5'-AGATAC-3' C. 5'-AAATTT-3'
D. 5'-CATAGA-3' E. 5'-CTTAGA-3'
19.The activation of amino acids for protein synthesis requires
A.one enzyme which activates all the amino acids.
B.one enzyme for forming amino acyl adenylates and one forming amino acyl tRNA.
C.several enzymes and DNA.
D.a different enzyme for each of the twenty amino acids used to make proteins.
E.a series of enzymes each with a broad specificity for amino acids of similar structure.
20.An important feature of an origin of DNA replication is:
A. a specific sequence recognized by DNA polymerase
B. a specific sequence recognized by topoisomerase
C. an AT-rich region D. a GC-rich region
E. a sequence containing a nick at a specific site
21.Which of the following DOES NOT play a role in prokaryotic replication?
A.DNA ligase B.reverse transcriptase C.DNA helicase
D.primase E. DNA polymerase I
22.Which of the following enzymes are involved in the EXCISION-REPAIR of UV-induced
pyrimidine dimers?
A. an endonuclease B. DNA ligase C. DNA polymerase I
D. photoreactivating enzyme (DNA photolyase) E. DNA gyrase
23.What is the function of the 3' to 5' exonuclease activity of bacterial DNA polymerases?
A.removes mismatched bases during replication B.removes pyrimidine dimers
C.removes the RNA primers of Okazaki fragments
D.initiates mRNA synthesis E.processes precursors of ribosomal RNA
24.Major enzyme of DNA replication in eukaryotes is
A. Pol B. Pol C. Pol D. Pol E. Pol 25.All of the following statements are true concerning DNA synthesis EXCEPT:
A.An RNA-DNA hybrid occurs at one stage.
B.DNA is replicated by several DNA polymerases, one of which can synthesize DNA in a 3'
to 5' direction and another of which synthesizes DNA in a 5' to 3' direction.
C.The primer for DNA synthesis is RNA.
D.DNA synthesis is discontinuous on the lagging strand in the sense that small fragments of
DNA are made first and then sealed together into long strands.
E.DNA synthesis is semi-conservative which means that daughter cells contain one
complete parental DNA strand and one complete new DNA strand.
26.Processing of a tRNA molecule includes all of the following except:
A. removal of nucleotides from the 5' end B. removal of nucleotides from the 3' end
C. addition of nucleotides to the 3' end
D. methylation and other base modifications E. removal of introns by spliceosomes
27.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
28.All of the following statements concerning DNA replication in prokaryotes are true EXCEPT
which one?
A.Replication is bidirectional from a single initiation point.
B.Okazaki fragments are joined by DNA polymerase III.
C.DNA polymerase III utilizes RNA oligonucleotides as primers.
D.Replication occurs in a 5' 3' direction.
E.Unwinding of the double helix requires ATP hydrolysis.
29.All of the following are true for both DNA polymerase and RNA polymerase EXCEPT which
one?
A. both require a template B. both reactions produce pyrophosphate as a product
C. both add 5' nucleotides to 3' hydroxyl groups
D. both utilize nucleotide triphosphates as substrates E. both require a primer
30.Sigma factor is involved in which of the following?
A. initiation of protein synthesis B.termination of protein synthesis
C.recognition of promoters by RNA polymerase
D.termination of transcription by RNA polymerase E.binds to Lac operator
31.Which of the following is not true of the prokaryotic (E. coli) transcriptional process?
A. specific sequences in the promoter are necessary for stable binding of RNA polymerase
B. A separate helicase enzyme is necessary for unwinding the DNA template to create an
open complex
C. during transcriptional elongation base pairing between the new RNA molecule and the
template strand of DNA is important
D. sigma factor is required only during the initiation process
E. termination requires special sequences (signals) in the nascent RNA chain
32.RNA polymerase is bound initially to which part of an operon?
A.promoter B.operator C.structural genes D.regulator genes E.enhancer
33.Control by attenuation (as in the trp operon) can occur only in prokaryotes because:
A. it requires coupling of transcription and translation
B. hairpin loops in RNA are more stable in bacteria
C. prokaryotic genes are often organized as operons
D. eukaryotic transcription does not have specific termination signals
E. repressor molecules are only found in prokaryotes
34.Initiation of mRNA transcription in a eukaryote
A. involves a group of basal transcription factors that are required to position RNA
polymerase at the transcriptional start site
B. does not require specific DNA sequences
C. is not a regulated step for determining the level of gene expression
D. requires canonical -10 and -35 sequences
E. requires sequence specific binding by the RNA polymerase itself
35.Which of the following are not matched correctly?
A. RNA splicing—occurs in the nucleus
B. snRNP—splicing out exons from the transcript
C. poly-A tail—increased transcript stability
D. RNA splicing—remove introns and ligate exons
E. All are matched correctly
36.Which statement most correctly describes the polarity of synthesis of RNA and protein, and the
direction of movement of the ribosome along mRNA?
A.RNA: 3' to 5'
Protein: N terminal to C terminal
Ribosome movement: 5' to 3'
B.RNA: 5' to 3'
Protein: N terminal to C terminal
Ribosome: 3' to 5'
C.RNA: 3' to 5'
Protein: C terminal to N terminal
Ribosome: 3' to 5'
D.RNA: 5' to 3'
Protein: N terminal to C terminal
Ribosome: 5' to 3'
37.Peptidyl transferase
A. is an intrinsic enzymatic activity of the large ribosomal subunit and requires an RNA
component
B. utilizes the energy of GTP hydrolysis to catalyze peptide bonds
C. transfers peptidyl-tRNA from the P site to the A site
D. recognizes signal peptides for transfer of nascent polypeptides to the RER
E. mimics an aminoacyl transferase and binds to the A site to cause termination of
translation
38.Post-translational modifications of polypeptides include all the following EXCEPT which one?
A.disulfide bond formation B.removal of methionine C.protease cleavage
D.capping by 7-methylguanidine E.attachment of prosthetic groups
39.The three-nucleotide codon system can be arranged in combinations.
A. 16 B. 20 C. 32 D. 64 E. 128
40.What will be the effect of a single base deletion in the middle of a cistron on the protein coded
for by this cistron? (Assume that there is no premature termination codon)
A.A protein with a single amino acid substitution in its center will be produced.
B.The cistron will not be transcribed and therefore no product will be produced.
C.The complete amino acid sequence of the protein will be abnormal.
D.This is a missense mutation and therefore the protein may remain functional.
E.The carboxyl half of the protein will have an altered sequence.
41.In eukaryotes, 28S, 5.8S, and 18S ribosomal RNAs
A. are all encoded by separate genes that are transcribed by RNA polymerase I
B. are all synthesized as one large precursor molecule that is subsequently cleaved to release
the 3 RNAs
C. are encoded by one large gene that undergoes splicing to produce the final RNA products
D. are encoded by a single copy gene that is expressed at extremely high levels because of
its localization to the nucleolus
E. are assembled into ribosomes as part of the translation initiation process in the cytosol
42.The genetic code is degenerate means:
A. one codon codes for more than one amino acid
B. there is more than one codon for some amino acids
C. both DNA strands are used as templates for mRNA synthesis
D. the code varies from species to species
E. there is more than one aminoacyl tRNA synthetase for each amino acid
43.The most important step in maintaining fidelity of the translation process is
A. joining of the correct amino acid and tRNA by aminoacyl-tRNA synthetases
B. proper methylation of tRNAs
C. correct base pairing between the codon and anticodon
D. peptide bond formation by peptidyl transferase E. none of the above are involved
44.Each amino acid in a protein is specified by
A. several genes B. a promoter C. an mRNA molecule D. a codon E. anticodon
45.Which of the following are useful antibacterial agents since they block protein synthesis in
prokaryotes but not eukaryotes (in vivo)?
1. streptomycin
2. cycloheximide
3. puromycin
4. diphtheria toxin
A. 1
B. 1 and 3
C. 2 and 4
D. 1, 2 and 3
E. all of them
46.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
47.Which of the following is not a true statement concerning the genetic code
A. some amino acids are coded for by more than one triplet
B. the same code is used by humans and E. coli
C. all 64 possible triplet sequences code for amino acids
D. the code is non-overlapping in an mRNA
E. there are no gaps between successive codons in an mRNA
(i.e. it is commaless)
48.All of the following reactions are involved in the formation of a fully functional tRNA from
precursor tRNA in a eukaryotic cell EXCEPT
A.removal of extra nucleotide sequences from the 5' end of the precursor molecule.
B.addition of a short poly A sequence to the 3' end.
C.addition of the sequence CCA to the 3' end.
D.removal of extra nucleotide sequences from the 3' end of the precursor molecule.
E.modification of individual bases in the tRNA molecule.
49.GTP hydrolysis is required for each of the following activities in protein synthesis EXCEPT
A. chain initiation B. implanting aminoacyl-tRNA into the A site
C. the peptidyltransferase reaction D. translocation
E. chain termination and dissociation of the ribosomal subunits
50.Codon-anticodon interactions
A.take place between mRNA and tRNA B.apply only to suppressor tRNAs
C.involve base-pairing between mRNA and rRNA
D.refer to interactions with the three termination codons
E.involve base-pairing between tRNAs and amino acids
51.The concept of "wobble" involves:
A. base pairing between the first (5') base of the codon and the third (3') base of the
anticodon
B. base pairing between the first base of the codon and the first base of the anticodon
C. base pairing between the third base of the codon and the first base of the anticodon
D. base pairing between the third base of the codon and the third base of the anticodon
E. none of the above are correct
52.Which of the following is a true statement?
A. since AUG serves as the start codon methionine is generally found only at the N terminus
of a protein
B. in eukaryotes the same aminoacyl-tRNA is used for the start codon as for internal AUG
sequences
C. in E. coli the same aminoacyl-tRNA is used for the start codon as for internal AUG
sequences
D. in translation of a eukaryotic mRNA the first AUG sequence almost always serves as the
start codon
E. since AUG serves as the start codon methionine is always the N-terminal amino acid in
mature proteins
53.ATP is directly required in protein biosynthesis for
A.movement of mRNA on the ribosome.
B.the activation of the amino group for peptide bond synthesis.
C.the formation of amino acyl-AMP.
D.the attachment of the ribosome to transfer RNA.
E.the formation of an "initiation complex".
54.The nucleolus is the site of
A.messenger RNA synthesis. B.protein synthesis.
C.ribosomal RNA synthesis. D.spindle fiber attachment. E.tRNA synthesis
55.During the process of peptide chain elongation, the growing peptide chain
A.is linked to the mRNA. B. is linked to the ribosomal RNA.
C.is not linked at all to any RNA.
D.is linked to the 3'-OH of the adenosine terminal nucleoside of tRNA.
Answer:
1-5 CAABE 6-10 AAEBA 11-15DADCD 16-20 CCEDC 21-25 BDADB
26-30 ECBEC 31-35 BAAAB 36-40 DADDE 41-45 BBADA 46-50 CCBCA
51-55 CBCCD
PART II.Give the efinition to the following:
1. de novo synthesis pathways of nucleotides
2. salvage pathways of nucleotides
3. central dogma of molecular biology
4. DNA replication
5. semiconservative replication
6. Okazaki fragment
7. reverse transcription
8. semi-discontinuous replication
9. transcription
10. asymmetry transcription
11. structural genes
12. Coding strand
13. Template strand
14. Pribnow box
15. exon
16. intron
17. RNA splicing
18. translation
19. genetic codon
20. signal peptide
21. polysome
PART III. Short questions.
1. Compare the differences and similarities of the de novo synthesis pathways of purine and
pyrimidine nucleotides according to materials and characteristics.
2. Compare the differences between the carbamoyl phosphate synthetaseⅠ(CPSⅠ) and CPSⅡ.
3. What are the end products of catabolism of purine base, cytosine, uracil and thymine?
4. What kinds of enzymes take part in DNA replication process of prokaryotes? Elaborate their
functions respectively.
5. Narrate DNA replication system.
6. Name three enzymatic activities of DNA polymerase I.
7. Narrate the process of reverse transcription.
8. What types of gene mutation are there according to molecule change?
9. What types of DNA repair are there? Narrate the process of excision repair.
10. Compare the differences and similarities between DNA replication and RNA transcription.
11. Narrate RNA transcription system.
12. Compare the difference of RNA polymerase of prokaryotes and eukaryotes.
13. Describe the post-transcriptional modification of eukaryotic hnRNA.
14. Describe the post-transcriptional modification of eukaryotic tRNA precursor.
15. Describe the various features of the Genetic Code.
16. Narrate the functions of 3 kinds of RNA involved in protein biosynthesis.
17.Briefly describe the translation process of prokaryotes.
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