Download 清华大学本科生考试试题专用纸

清华大学本科生考试试题专用纸
考试课程
Biochemistry II
2001
年
6 月 11
日
说明：1. 请选择正确答案，填在适当的横线处（1-30 题）或写在答题纸上（31-33 题）
；
2. 答案可能是一个或多个；
3. 每题的分数在标在了题目后面；
4. 本卷满分为 100.
1. If the G` of the reaction A
B is –12 kJ/mol, which of the following statements
are correct? (Note the prime symbol means that a thermodynamic parameter is measured
at pH.7.0) (2 points)
A.
B.
C.
D.
The reaction will proceed spontaneously from left to right at the given conditions.
The reaction will proceed spontaneously from right to left at standard conditions.
The equilibrium constant favors the formation of B over the formation of A.
The equilibrium constant could be calculated if the initial concentrations of A and B were
known.
E. The value of G`o is also negative.
Answer(s): A, D
2. Which of the following statements about ATP and its roles in cells are true? (2 points)
A. The ATP molecule is kinetically unstable and is thus consumed within about one minute
following its formation in cells.
B. ATP provides free energy to a thermodynamically unfavorable reactions by group transfer,
always donating a Pi to form a covalent intermediate.
C. ATP can be regenerated by coupling with a reaction that releases more free energy than does
ATP hydrolysis.
D. A transmembrane proton-motive force can drive ATP synthesis.
E. The active form of ATP is usually in a complex with Mg2+.
Answer(s): C, D, E
3. A common moiety for NADP, NAD, FMN, FAD, and coenzyme A is: (2 points)
A. A pyrimidine ring;
B. A three ring structure;
C. An ADP;
D. A pyranose ring;
E. A triphosphate group.
Answer(s): C
4. If the C-1 carbon of glucose were labeled with 14C, which of the carbon atoms in pyruvate would
be labeled after glycolysis? (2 points)
A. The carboxylate carbon;
B. The carbonyl carbon;
C. The methyl carbon.
Answer(s): C
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5. Which of the following are metabolic products of pyruvate in higher organisms? (2 points)
A. Glycerol
B. Lactic acid
C. Acetone
D. Acetyl-CoA
E. Ethanol
Answer(s): B, D
6. Indicate whether each of the following statements about the pentose phosphate pathway is true (T)
or false (F). (5 points)
A. It generates NADH for reductive biosyntheses. F
B. The reactions occur in the cytosol. T
C. Transketolase and transaldolase link this pathway to gluconeogenesis. F
D. It is more active in muscle cells than in fat-storage cells. F
E. It interconverts trioses, tetroses, pentoses, hexoses, and heptoses. T
7. Which of the following statements are correct? The citric acid cycle (2 points)
A. does not exist as such in plants and bacteria, because its functions are performed by the
glyoxylate cycle.
B. oxidizes acetyl CoA derived from fatty acid degradation.
C. produces most of the CO2 in anaerobic organisms.
D. provides succinyl CoA for the synthesis of carbohydrates.
E. provides precursors for the synthesis of glutamic and aspartic acids.
Answer(s): B, E
8. Match the cofactors of the pyruvate dehydrogenase complex with their corresponding enzyme
components and with their roles in the enzymatic steps that are listed. (5 points)
A. Coenzyme A: 3,7
B. NAD+: 2, 9
C. Thiamine pyrophosphate (TPP): 1, 5
D. FAD: 2, 6
E. Lipoamide: 3, 4,8
(1). Pyruvate dehydrogenase component
(2). Dihydrolipoyl dehydrogenase
(3). Dihydrolipoyl transacetylase
(4). Oxidizes the hydroxylethyl group
(5). Decarboxylates pyruvate
(6). Oxidizes dihydrolipoamide
(7). Accepts the acetyl group from acetyllipoamide
(8). Provides a long, flexible arm that coveys intermediates to different enzyme component.
(9). Oxidizes FADH2.
9. Matching the role in fatty acid oxidation and/or mobilization to the appropriate component listed
below. (5 points)
A. Bile salt: 2
B. Serum albumin:5
C. ApoC-II:4
D. Apolipoprotein:3
E. Carnitine:1
(1). Acts as a “carrier” of fatty acids across the inner mitochondrial membrane.
(2). Acts as a biological detergent, disrupting fat globules into small mixed micelles.
(3). Binds and transports triacylglycerols, phospholipids, and cholesterol between organs.
(4). Activates lipoprotein lipase, which cleaves triacylglycerols into their components.
(5). Binds some fatty acids molibized from adipocytes and transports them in the blood to heart
and skeletal muscle.
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10. Which of the following answers complete the sentence correctly? Surplus dietary amino acids
may be converted into (2 points)
A. proteins.
B. Fats.
C. ketone bodies.
D. glucose.
E. a variety of biomolecules for which they are precursors.
Answer(s): A, B, C, D,E
11. Which of the following compounds serves as an acceptor for the amino groups of many amino
acids during metabolism? (2 points)
A. Glutamine
B. Asparagine.
C. -ketoglutarate.
D. Oxaloacetate
E. Glutamate
Answer(s):C
12. Match the functions for the coenzymes that are involved in amino acid metabolism. (4 points)
A. Pyridoxal phosphate: (3)
B. Coenzyme B12: (2)
C. Tetrahydrobiopterin: (1)
D. NAD+: (1)
E. Biotin (4)
(1). Carries electrons
(2). Provides free radicals
(3). Carries amino groups
(4). Carries CO2.
13. Which of the following experimental observations would not support the chemiosmotic model of
oxidative phosphorylation? (3 points)
A. If mitochondrial membranes are ruptured, oxidative phosphorylation cannot occur.
B. Raising the pH of the fluid in the intermembrane space results in ATP synthesis in the
matrix.
C. Transfer of electrons through the respiratory chain results in formation of a proton gradient
across the inner mitochondrial membrane.
D. The orientation of the enzyme complexes of the electron transfer chain results in a
unidirectional flow of H+.
E. Radioactively labeled inorganic phosphate is incorporated into cytosolic ATP only in the
presence of an H+ gradient across the inner mitochondrial membrane.
Answer(s): B
14. Some photosynthetic prokaryotes use H2S, hydrogen sulfide, instead of water as their
photosynthetic hydrogen donor. How does this change the ultimate products of photosynthesis? (2
points)
A. Carbohydrate (CH2O) is not produced.
B. H2O is not produced.
C. Oxygen is not produced.
D. ATP is not produced.
E. The products do not change.
Answer(s): C
15. Which of the following are constituents of chlorophylls? (2 points)
A. Substituted tetrapyrrole.
B. Plastoquinone.
C. Mg2+.
D. Fe2+.
E. Phytol.
F. Iron porphyrin.
Answer(s): A, C, E
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16. The observation that the incubation of photosynthetic algae with 14CO2 in the light for a very brief
time (5s) led to the formation of 14C-labeled 3-phosphoglycerate suggested that the 14CO2 was
condensing with some two-carbon acceptor. That acceptor was in fact which of the following? (2
points)
A. Acetate
B. Acetyl CoA
C. Acetyl phosphate
D. Acetaldehdyde
E. Glycerol phosphate
F. None of the above
Answer(s): F
17. Which of the following are common features of the syntheses of mevalonate (an intermediate of
cholesterol biosynthesis) and ketone bodies? (2 points)
A. Both involve 3-hydroxyl-3-methylglutaryl CoA (HMG-CoA).
B. Both require NADPH.
C. Both require the HMG-CoA cleavage enzyme.
D. Both occur in the mitochondria.
E. Both occur in liver cells.
Answer(s): A
18. S-adenosylmethionine is involved directly in which of the following reactions. (3 points)
A. Methyl transfer to phosphatidyl ethanolamine.
B. Synthesis of glycine from serine.
C. Synthesis of polyamines.
D. Conversion of homocysteine to methionine.
E. Generation of the 5` cap of the eukaryotic mRNAs.
Answer(s): A, C, E
19.Which of the following does not provide a carbon skeleton for the synthesis of amino acids? (2
points)
A. succinate.
B. -ketoglutarate
C. Pyruvate.
D. Oxaloacetate.
E. Ribose-5-phosphate.
Answer(s): A
20. Which of the following compounds directly provide atoms to form the purine ring? (3 points)
A. Aspartate.
B. Carbamoyl phosphate.
C. Glutamine.
D. Glycine.
E. CO2.
F. N5,N10-methylenetetrahydrofolate.
G. N10-formyltetrahydrofolate.
H. NH4+.
Answer(s): A, C, D, E, G
21. Which of the following statements about ribonucleotide reductase are true? (2 points)
A. It converts ribonucleoside diphosphates into 2`-deoxyribonucleoside diphosphates in
humans.
B. It contains coenzyme B12, which generates free radicals needed for the catalysis.
C. It accepts electrons directly from FADH2.
D. It receives electrons directly from either thioredoxin or glutaredoxin.
E. It contains two kinds of allosteric regulatory sites: one for controlling the overall activity
and the other for controlling the substrate specificity.
Answer(s): A, D, E
22. Biosynthetic pathways that require NADPH include which of the following? (2 points)
A. Gluconeogenesis.
B. Fatty acid biosynthesis.
C. Ketone body formation.
D. Cholesterol biosynthesis.
E. Tyrosine biosynthesis.
Answer(s): B,D,E
23. Homologous recombination in E. coli is likely to require which of the following? (3 points)
A. DnaB protein.
B. RecA protein.
C. RecBCD complex.
D. ATP.
E. NAD+.
F. Single-strand DNA binding protein.
G. DNA-dependent RNA polymerase.
H. DNA polymerase I.
I. DNA ligase.
J. dATP.
Answer(s): B, C, D, E, F, H, I, J
24. Which of the following statements about E. coli promoters are correct? (2 points)
A. They may exhibit different transcription efficiencies.
B. For most genes they include variants of consensus sequences.
C. They specify the start sites for transcription on the DNA template.
D. They have identical and defining sequences.
E. They are activated when C or G residues are substituted into their –10 regions by mutation.
F. Those that have sequences that correspond closely to the consensus sequences and are
separated by 17 base pairs are very efficient.
Answer(s): A, B, C, F
25. The AAUAAA sequence on a RNA molecule marks (2 points)
A. The site where ribosomes bind to initiate polypeptide synthesis.
B. The site where transcription stops.
C. The site near which the primary transcript is cleaved and a poly (A) sequence is added.
D. The site where the release factor will bind to end polypeptide synthesis.
E. The site where polyribonucleotide phosphorylase will add a stretch of random sequences.
Answer(s): C
26. The 70 subunit of the E. coli RNA polymerase: (2 points)
A. acts as the catalytic site for polymerization.
B. Recognize promoters.
C. Has a proofreading function.
D. Increases the processivity of the enzyme.
E. Recognizes termination signals.
Answer(s): B
27. The discontinuity of eukaryotic genes were first revealed by: (2 points)
A. Using footprinting techniques.
B. DNA sequence comparison.
C. RNA sequence analysis.
D. Electron microscopic analysis of RNA-DNA hybrid molecules.
E. Plant genetic studies.
Answer(s): D
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28. Which of the following mRNA codons can be recognized by the tRNA anticodon ICG. (2 points)
A. UGC.
B. CGA.
C. UGA.
D. CGU.
E. CGC.
Answer(s): B, D, E
29. A new compound, vivekine, was recently discovered by a clever undergraduate student. It was
isolated from bacteria found in deep sea-dwelling organisms. Vivekine inhibits protein synthesis in
eukaryotes: Protein synthesis can initiate, but only dipeptides are formed and these remain bound to
the ribosome. This toxin affects eukaryotic protein synthesis by blocking the: (2 points)
A. binding of formylmethionyl-tRNA to ribosomes.
B. activity of elongation factors.
C. activation of amino acids.
D. recognition of stop signals.
E. formation of peptide bonds.
Answer(s): B
30. Indicate whether each of the following statements about prokaryotic translation is true (T) or false
(F). (7 points)
A. An aminoacyl-tRNA synthetase catalyzes formation of an ester bond. ( T )
B. An mRNA molecule cannot be used to direct protein synthesis until it has been completely
transcribed. ( F )
C. The positioning of fMet-tRNA on the A site defines the reading frame. ( F )
D. Incoming aminoacyl-tRNA are first bound to the A site. ( T )
E. Formation of the 70S initiation complex requires an input of energy. ( T )
F. The carboxyl group of the amino acid on the aminoacyl-tRNA is transferred to the amino
group of a peptidyl-tRNA.( F )
G. Release factors cause the peptidyl transferase activity of the ribosome to use H2O as a
substrate. ( T )
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31. In an attempt to determine whether a given RNA was catalytically active in the cleavage of a
synthetic oligonucleotide, the following experimental results were obtained. When the RNA and the
oligonucleotide were incubated together, cleavage of the oligonucleotide occurred. When either the
RNA or the oligonucleotide was incubated alone, there was no cleavage. When the RNA was
incubated with higher concentrations of the oligonucleotide, saturation kinetics of the
Michaelis-Menten type were observed. Do these results demonstrate that the RNA has catalytic
activity? Explain. (8 points)
Answer:
These results alone do not establish that the RNA has catalytic activity. A
catalyst must be regenerated. It is entirely possible that the results observed could be
accounted for by a stoichiometric, as opposed to a catalytic, interaction between RNA and
the oligonucleotide. In which the RNA may “commit suicide” as the oligonucleotide is
cleaved. In such an interaction, a portion of the RNA would also be cleaved itself as a part
of the reaction. Four reaction products would accumulate, two resulting from the cleavage
of RNA and two from the cleavage of the oligonucleotide. To show that this particular RNA
was catalytic, it would be necessary to demonstrate that it turns over and is regenerated in
the course of the reaction.
32.Translation involves conversion of the language of nucleotides to that of proteins. In the chain of
events leading from a nucleotide sequence on DNA to the production of protein by ribosomes, where
precisely does the process of translation occur? Explain. (6 points)
Answer: Translation involves conversion of the language of nucleotides to that of proteins. The
agent of translation is the appropriate aminoacyl-tRNA synthetase, which must recognize a particular
amino acid and link it to a tRNA containing an anticodon for that amino acid.
33.Suppose that a bacterial mutant is found to replicate its DNA at a very low rate. Upon analysis, it
is found to have entirely normal activity of DNA polymerases I and III, DNA gyrase, and DNA
ligase. It also makes normal amounts and kinds of dnaA, dnaB, dnaC, and SSB proteins. The oriC
region of its chromosome is found to be entirely normal with respect to nucleotide sequence. What
defect might account for the abnormally low rate of DNA replication in this mutant? Explain. (6
points)
Answer: A decrease in the activity of primase would account for the low rate of DNA replication.
DNA replication requires the prior synthesis of RNA primers. Decreased rates of dNTP synthesis
would also slow replication.
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