生物化学下生化复习历年真题

1、PAGE 第9页/共 9 页清华大学本科生考试试题专用纸 (A)考试课程 Biochemistry II 2005 年 1 月 15 日说明：1. 第140题为选择题，每题2分，答案可能是一个或多个，请将 正确答案填在适当的横线处；2. 第4144题为问答题，每题的分数标在了题目后面，请将答案写 在答题纸上；3. 本卷满分为100。1. Which compound links glycolysis, nucleotide synthesis, and glycogen synthesis?acetyl-CoA oxaloacetatecitrateglucose 6-phosphategly

2、cerol 3-phosphateAnswer(s): D2. You have discovered a compound that inhibits fumarase. How many moles of ATP would you expect to be generated from one mole of acetyl-CoA in the presence of this inhibitor? 566.57.5No ATP would form under these conditions.Answer(s): D3. Indicate which of the following

3、 events can occur during the processing of eukaryotic mRNA transcripts. Attachment of a poly (A) tail to the 5 end of the transcript.Methylation of all G residues.Excisions of introns.Conversion of standard bases to modified bases such as inosine.Splicing together of exons.Differential cutting and s

4、plicing to produce two different proteins.Answer(s): CE4. Although DNA replication has very high fidelity, mutations do occur. Which of the following types of single base-pair mutations would be most likely to be a lethal mutation? substitutioninsertiondeletionsilentB and CAnswer(s): E5. Which of th

5、e following correctly describes the nitrogen cycle? Fixation of atmospheric nitrogen by nitrogen-fixing bacteria yields bioavailable nitrate.Nitrate is reduced to ammonia in a process known as denitrification.Biological nitrogen fixation is carried out by a complex of proteins call the nitrogenase c

6、omplex.A and BA, B, and CAnswer(s): C6. Assuming the 5 3 connection of writing nucleotide sequence, indicate which of the following mRNA codons can be recognized by the tRNA anticodon ICG. UGCCGAUGACGUCGCAnswer(s): BDE7. Both general recombination and transposon-type recombination: occur between hom

7、ologous regions on chromosomes.are important in the repair of damaged DNA.involve RecA protein.generate genetic diversity.The two types of recombination have nothing in common.Answer(s): D8. Consider the mRNA sequence: (5) AAUGCAGCUUUAGCA (3). The sequence of the coding strand of DNA is: (5) ACGATTT

8、CGACGTAA (3)(3) TTACGTCGAAATCGT (5)(5) AATGCAGCTTTAGCA (3)(5) AAUGCAGCUUUAGCA (3)(3) AATGCAGCTTTAGCA (5)Answer(s): C9. The synthesis of palmitate requires: 8 acetyl-CoA.14 NADH.7 ATP.A and C.A, B, and C.Answer(s): D10. Enoyl-CoA isomerase is needed for the complete -oxidation of unsaturated fatty ac

9、ids with cis double bonds.odd-number fatty acids.saturated fatty acids.unsaturated fatty acids with trans double bonds. Answer(s): A11. Which of the following is a characteristic of many aminotransferase reactions? They have a large, negative Go.The amino group is transferred to an -keto acid (such

10、as -ketoglutarate) to form the corresponding amino acid.The amino group is transferred from an ammonia molecule.They are catalyzed by the same enzyme.They require the cofactor S-adenosylmethionine.Answer(s): B12. If the G of the reaction A B is 12 kJ/mol, which of the following statements are correc

11、t? (Note the prime symbol means that a thermodynamic parameter is measured at pH 7.0) 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

12、B over the formation of A.The equilibrium constant could be calculated if the initial concentrations of A and B were known.The value of Go is also negative.Answer(s): AD13. Which of the following is not a physiological role of nucleotides? allosteric regulatorsintermediates for biosynthetic processe

13、scomponents of many proteinscomponents of the coenzymes NAD, FAD, and CoAintracellular signaling moleculesAnswer(s): C14. Indicate which of the following statements about the lac operon is true. All seven genes are transcribed into mRNA, which is then translated into five different proteins.The repr

14、essor binds to the structural genes, preventing their transcription.Efficient binding of RNA polymerase to DNA occurs only in the presence of CRP and cAMP.cAMP acts as an inducer by binding to the Lac repressor.In the absence of lactose, the repressor binds the operator.A mutation in the I gene such

15、 that no gene product is made leads to constitutive expression of the Z, Y, and A genes.Answer(s): CEF15. Which pair correctly matches the enzyme with its allosteric activator? hexokinase; ATPphosphofructokinase-1; AMPpyruvate kinase; ATPpyruvate dehydrogenase: NADHpyruvate carboxylase; ADPAnswer(s)

16、: B 16. Which of the following describes fatty acid transport into the mitochondrial matrix? It is the rate-limiting step in fatty acid oxidation.It is regulated by malonyl-CoA.The cytosolic and matrix pools of CoA are distinct and separate.Once fatty acyl groups have entered the matrix, they are co

17、mmitted to oxidation to acetyl-CoA.All of the above are true.Answer(s): E17. In nucleotide metabolism, all of the following are true except: The commitment step in purine biosynthesis is the transfer of amino group to PRPP.Both purine and pyrimidine biosynthesis are regulated by end-product inhibiti

18、on.Nucleotides can be synthesized in a single reaction via salvage pathways.De novo pyrimidine synthesis begins with a molecule of PRPP.Orotidylate is the common precursor in the biosynthesis of pyrimidines, and inosinate is the common precursor in the biosynthesis of the purines ATP and GTP.Answer(

19、s): D18. The most efficient way to turn off glycogen degradation is to: decrease the activity of phosphorylase kinase.increase the activity of phosphodiesterases.increase the activity of phosphatases.increase the activity of glycogen synthase.decrease the intracellular levels of cAMP.Answer(s): E19.

20、 In some respects, the urea cycle and the citric acid cycle are analogous processes. Ornithine and citrulline have roles that are similar to those of oxaloacetate and what other citric acid cycle intermediate? acetyl-CoAmalatecitrateammoniaCO2Answer(s): C20. Indicate which of the following statement

21、s about the mitochondrial electron transfer and oxidative phosphorylation are true. Synthesized ATP must be transported into the intermembrane space before it can enter the cytosol.Cytochrome c and the F1 subunit of ATPase are peripheral membrane proteins.Complexes I, II, III and IV are all proton p

22、umps.Ubiquinone is a hydrophilic molecule.The final electron acceptor is H2O.Answer(s): AB21. Which of the following describes the activity and regulation of ribonucleotide reductase and/or its importance to the cell? Both of its activity and its substrate specificity are regulated by the binding of

23、 effector molecules.ATP increases the overall activity of the enzyme.Control of the enzymes activity ensures a balanced pool of precursors for DNA synthesis.Balanced pools of deoxyribonucleotides are necessary in DNA synthesis, given the complementary base-pairing of nucleotides in double-stranded D

24、NA.All of the above are true.Answer(s): E22. Earlier in its life, a tadpole lives in an aqueous environment and excretes much of its excess nitrogen as ammonia. Once it matures into an adult, the frog spends much time on dry land and becomes ureotelic. Which of the following enzyme activities would

25、be most likely to increase drastically in the adult frog? carbamoyl phosphate synthetase Iglutamine synthetaseglutaminase-ketoglutarate dehydrogenasecarboxypeptidaseAnswer(s): A23. The discontinuity of eukaryotic genes was first revealed by: using footprinting techniques.DNA sequence comparison.RNA

26、sequence analysis.electron microscopic analysis of RNA-DNA hybrid molecules.plant genetic studies.Answer(s): D24. Ames Test is used to investigate whether a chemical reagent is: oxidative.reductive.mutagenic.enzymatic.Answer(s): C25. A sample of malonyl-CoA synthesized from radioactive (14C labeled)

27、 HCO3- and unlabeled acetyl-CoA is used in fatty acid synthesis. In which carbon(s) will the final fatty acid be labeled? (Recall that the carboxyl carbon is C-1.) every carbonevery odd-numbered carbonevery even-numbered carbononly the carbon farthest from C-1no part of the molecule will be labeled.

28、Answer(s): E26. Not taking into account the NADH generated in the malate dehydrogenase reaction, how many high-energy phosphate bonds are used to form a molecule of urea, starting from ammonia and HCO3-? 12340Answer(s): D27. DNA polymerase I has: 3 5 exonuclease activity.5 3 exonuclease ofreading ac

29、tivity.polymerase activity.Answer(s): ABCD28. The proton-motive force generated by the electron transfer chain: includes a pH-gradient component.includes an electrical-potential component.is used for active transport processes.is used to synthesize ATP.has all of the above characteristics.Answer(s):

30、 E29. Which statement is not true of phosphofructokinase-1? It is inhibited by fructose 2, 6-bisphosphate.It is activated by AMP.It is inhibited by citrate.It is inhibited by ATP.ATP increases its K0.5 for fructose 6-phosphate.Answer(s): A30. Some photosynthetic prokaryotes use H2S, hydrogen sulfide

31、, instead of water as their photosynthetic hydrogen donor. How does this change the ultimate products of photosynthesis?Carbohydrate (CH2O) is not produced.H2O is not produced.Oxygen is not produced.ATP is not produced.The products do not change.Answer(s): C31. Which of the following answers complet

32、e the sentence correctly? Surplus dietary amino acids may be converted into proteins.fats.ketone bodies.glucose.a variety of biomolecules for which they are precursors.Answer(s): ABCDE32. Human chromosomes are extremely large, complex structures. Which of the following statements correctly describes

33、 the organization of the human chromosomes? All of the genetic information of the cell is encoded in the nuclear, chromosomal DNA.Genes for histones and ribosomal RNAs are structural genes.Most of the chromosomal DNA codes for proteins.A and B.A, B, and C.Answer(s): B33. Methylation of GATC sequence

34、s at _ is believed to control the replication frequencies in E. coli cells.oriCTERThe leading strandThe lagging strandAnswer(s): A34. _ causes premature termination of polypeptide synthesis by mimicking aminoacyl transfer RNA: it is able to enter the A site and accept the peptidyl group to form a pe

35、ptidyl molecule, which however will dissociate from the ribosome. Tetracyclin PuromycinChloramphenicol Streptomycin Answer(s): B35. Which of the following compounds do not directly provide atoms to form the purine ring? Aspartate.Carbamoyl phosphate.Glutamine.Glycine.CO2.N5, N10-methylenetetrahydrof

36、olate.N10-formyltetrahydrofolate.NH4+.Answer(s): BFH36. Which of the following is true of the control of gluconeogenesis? Glucagon stimulates adenylyl cyclase, causing the formation of cAMP.Cyclic AMP stimulates the phosphorylation and thus increases the activity of FBPase-2.FBPase-2 activity lowers

37、 the level of fructose-2, 6-bisphosphate, thus increasing the rate of gluconeogenesis.It is reciprocally linked to the control of glycolysis.All of the above are true.Answer(s): E37. Carbon fixation involves a condensation reaction between CO2 and:3-phosphoglycerate.phosphoglycolate.ribulose 1, 5-bi

38、sphosphate.fructose 6-phosphate.ribose 5-phosphate.Answer(s): C38. How do the hormones epinephrine and glucagon differ in their metabolism of glucose? Only epinephrine stimulates glyconeogenesis.Only glucagon stimulates glyconeogenesis.Only epinephrine acts on muscle.Only glucagon stimulates glycoly

39、sis. Answer(s): C39. The enzyme(s) responsible for the transcription of eukaryotic rRNA is： RNA polymerase IRNA polymerase IIRNA polymerase IIIRNA polymerase I and IIIRNA polymerase II and IIIAnswer(s): D40. The enzymatic process of “charging” a molecule of tRNA is similar to other enzyme catalyzed

40、reactions you have encountered in this course. Which of the following correctly describes such similarities? Formation of an acyl-adenylate intermediate coupled to the hydrolysis of pyrophosphate is similar to reactions involved in fatty acid activation.Proofreading and correcting abilities that pre

41、vent incorporation of the wrong molecule are analogous to the action of DNA polymerase.The aminoacyl-tRNA synthetase is a relatively nonspecific enzyme (i.e. it can activate many different amino acids) and in the respect is similar to ribonucleotide reductase.A and BA and CB and CAnswer(s): D41. Exp

42、lain why skeletal muscle does not contribute glucose to the blood. (4 points)Answer: Because it lacks the enzyme glucose 6-phosphatase.42. Explain why untreated diabetics lose weight. (4 points)Answer: The rate of triacylglycerol biosynthesis is affected by the action of several hormones, one of whi

43、ch is insulin. Insulin promotes the conversion of carbohydrates to triacylglycerols. People with severe diabetes, due to failure of insulin secretion or action, not only are unable to use glucose properly but also fail to synthesize fatty acids from carbohydrates or amino acids. Untreated diabetics

44、have increased rate of fat oxidation and ketone body formation, as a consequence, lose weight.43. 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 amou