Sample Questions for Exam 3

Transcription

1 Sample Questions for Exam 3 1. All of the following occur during prometaphase of mitosis in animal cells except a. the centrioles move toward opposite poles. b. the nucleolus can no longer be seen. c. the nuclear envelope disappears. d. chromosomes replicate. e. the spindle is organized. 2. If there are 20 centromeres in a cell, how many chromosomes are there? a. 10 b. 20 c. 30 d. 40 e Where do the microtubules of the spindle originate during mitosis in both plant and animal cells? a. centromere b. centrosome c. centriole d. chromatid e. kinetochore 4. If a cell has 8 chromosomes at metaphase of mitosis, how many chromosomes will it have during anaphase? a. 1 b. 2 c. 4 d. 8 e During which phase(s) of mitosis do we find chromosomes composed of two chromatids? a. from interphase through anaphase b. from G1 of interphase through metaphase c. from metaphase through telophase d. from anaphase through telophase e. from G2 of interphase through metaphase 6. Movement of the chromosomes during anaphase would be most affected by a drug that a. reduced cyclin concentrations. b. increased cyclin concentrations. c. prevented elongation of microtubules. d. prevented shortening of microtubules. e. prevented attachment of the microtubules to the kinetochore.

2 7. What causes the rhythmic change in cyclin concentration in the cell cycle? a. an increase in production of a Cdk once the restriction point is passed b. the cascade of increased production once the protein is phosphorylated by Cdk c. the changing ratio of cytoplasm to genome d. its destruction by an enzyme phosphorylated by the cyclin-cdk complex e. the binding of PDGF to receptors on the cell surface 8. What are enzymes called that control the activities of other proteins by phosphorylating them? a. ATPases b. kinases c. cyclins d. chromatin e. phosphatases The questions below consist of three phrases or sentences concerned with the cell cycle. For each phrase or sentence, select the answer letter from below that is most closely related to it. Each answer may be used once, more than once, or not at all a. G0 b. G1 c. S d. G2 e. M 9. The restriction point occurs here. 10. the shortest part of the cell cycle 11. DNA is replicated at this time of the cell cycle. 12. A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. Those cells would have picograms at the end of the S phase and picograms at the end of G2. a. 8, 8 b. 8, 16 c. 16, 8 d. 16, 16 e. 12, 16

3 13. A particular cell has half as much DNA as some of the other cells in a mitotically active tissue. The cell in question is most likely in a. G1. b. G2 c. prophase. d. metaphase. e. anaphase. 14. Which of the following is true of the process of meiosis? a. Two diploid cells result. b. Four diploid cells result. c. Four haploid cells result. d. Four autosomes result. e. Four chiasmata result. 15. Crossing-over occurs during which phase of meiosis? a. prophase I b. anaphase I c. telophase I d. prophase II e. metaphase II Use the following key to answer the following questions. Each answer may be used once, more than once, or not at all a. The statement is true for mitosis only. b. The statement is true for meiosis I only. c. The statement is true for meiosis II only. d The statement is true for mitosis and meiosis I. e. The statement is true for mitosis and meiosis II. 16. This occurs when a cell divides to form two nuclei that are genetically identical. 17. Homologous chromosomes synapse and crossing over occurs. 18. Centromeres uncouple and chromatids are separated from each other.

4 19. The process(es) is (are) preceded by a copying (replication) of the DNA. 20. What happens when T 2 phages are grown in the presence of radioactive phosphorus? a. Their DNA becomes radioactive. b. Their proteins become radioactive. c. Their DNA is found to be of medium density in a centrifuge tube. d. They are no longer able to transform bacterial cells. e. They transfer their radioactivity to E. coli chromosomes during infection. 21. Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. What percent of the nucleotides in this sample will be thymine? a. 12 b. 24 c. 31 d. 38 e. It cannot be determined from the information provided. 22. All of the following statements apply to the Watson and Crick model of DNA except. a. The two strands of the DNA form a double helix. b. The distance between the strands of the helix is uniform. c. The framework of the helix consists of sugar-phosphate units of the nucleotides. d. The two strands of the helix are held together by covalent bonds. e. The purines are attracted to pyrimidines. 23. Which enzymes catalyze the elongation of a DNA strand in the 5 3 direction? a. primase b. DNA ligase c. DNA polymerases d. topoisomerase e. helicase 24. Which of the following help to hold the DNA strands apart while they are being replicated? a. helicase b. ligase c. DNA polymerase d. single-strand binding proteins e. primase

5 25. An eukaryotic cell lacking telomerase would a. have a high probability of becoming cancerous. b. produce Okazaki fragments. c. be unable to replicate. d. undergo a reduction in chromosome length. e. be highly sensitive to sunlight. 26. A particular triplet of bases in the coding sequence of DNA is AGT. The corresponding codon for the mrna transcribed is a. AGT. b. UCA. c. TCA. d. AGU. e. either UCA or TCA, depending on wobble in the first base. 27. Which of the following is correct about a codon? It a. consists of two nucleotides. b. may code for the same amino acid as another codon. c. consists of discrete amino acid regions. d. catalyzes RNA synthesis. e. is on the DNA molecule. 28. The genetic code is essentially the same for all organisms. From this, one can logically assume all of the following except: a. A gene from an organism could theoretically be expressed by any other organism. b. All organisms have a common ancestor. c. DNA was the first genetic material. d. Codons usually translate into the same amino acids. e. The genetic code was an early event in the evolution of life. 29. Where is the attachment site for RNA polymerase? a. structural gene region b. initiation region c. promoter region d. operator region e. regulator region

6 30. Which of the following helps to stabilize mrna by inhibiting its degradation? a. TATA box b. spliceosomes c. exons d. snrnps e. poly(a) tail 31. What are the coding segments of a stretch of eukaiyotic DNA called? a. introns b. exons c. codons d. replicons e. transposons 32. All of the fo!lowing are found in prokaryotic messenger RNA except a. the AUG codon. b. the UGA codon. c. introns. d. uracil. e. cytosine. 33. Once transcribed, eukaryotic mrna typically undergoes substantial alteration that includes a. excision of introns. b. fusion into circular forms known as plasmids. c. linkage to histone molecules. d. union with ribosomes. e. fusion with other newly transcribed mrna. 34. The codons in the genetic code that do not specify amino acids are called a. missense codons b. start codons c. stop codons d. promoters e. initiator codons

7 35. In eukaryotic cells, transcription and translation a. are separated. Translation occurs in the nucleus and transcription in the cytoplasm. b. occur together in the cytosol. c. occur together in the nucleus. d. are separated. Translation occurs in the cytoplasm and transcription in the nucleus. e. are separated, except for proteins that bind to the DNA and ribosomes, which are translated in the nucleus. 36. Telomerase is important to eukaryotic cells because a. telomeres tend to get shortened with each cell division. b. telomeres tend to get longer with each cell division. c. telomerase digests telomeres to proper length. d. the leading strand of DNA causes the telomeres to shorten. e. it aids in making artificial chromosomes. 37. Each human chromosome must have a. a centromeric sequence. b. telomeric sequences. c. an origin of replication. d. All of the above e. None of the above 38. RNA polymerase II by itself cannot bind to the chromosome and initiate transcription. It can bind and act only after the assembly of regulatory proteins called factors. a. translation b. post-translation c. initiation d. transcription e. None of the above 39. In bacteria, transcription a. is separate from translation. b. occurs in the nucleus. c. is not separated from translation. d. is the process of synthesizing proteins. e. is continuous for all genes.

8 40. The mrna will form hybrids only with the template strand of DNA because a. DNA will not re-anneal at high temperatures. b. the salt concentration will affect DNA re-annealing. c. DNA will not re-anneal at low temperatures. d. RNA DNA hybridization follows the base-pairing rules. e. denatured DNA will not re-anneal after it is diluted. 41. DNA sequences found in introns provide a. amino acid sequence information. b. regulatoiy information. c. no known useful information. d. structure for the gene. e. alternative DNA splicing possibilities. 42. Which of the following is not part of RNA processing in eukaryotes? a. Splicing of exons b. Reverse transcription c. Addition of a 5 cap d. Addition of a poly A tail e. Intron removal 43. Consensus sequences (short segments of DNA) appear in the transcribed regions of various genes. These sequences appear to be involved in a. directing the polymerases to the appropriate place on the DNA for transcription to begin. b. the splicing of introns out of the DNA. c. allowing the transcription to stop at the appropriate spot. d. catalyzing the synthesis of a protein. e. None of the above 44. The expression of some genes can be regulated in part by the pattern of RNA splicing. This is an example of a. DNA methylation. b. transcriptional regulation. c. catalytic RNA s. d. posttranscriptional control. e. the endo-symbiotic theory.

9 45. Which of the following best describes the function of the addition of a methylated guanosine cap to the 5 end of primary mrna? a. It contains all of the coding and noncoding sequences of the DNA template. b. It provides the mrna molecule with a poly A tail. c. It facilitates the binding of mrna to ribosomes. d. It forms hydrogen bonds. e. It helps transfer amino acids to the ribosomes. 46. The binding of snrnp s to consensus sequences is necessary for a. gene duplication. b. addition of a poly A tail. c. capping an hnrna. d. RNA splicing. e. transcription. 47. The modified G cap on eukaryotic mrnas is found a. at the 5 end. b. at the 3 end. c. in the consensus sequence. d. in the poly A tail. e. in snrna. 48. In eukaryotic cells, a repressor a. is made of DNA. b. binds to the enhancer region to block transcription. c. is located both upstream and downstream from the promoter. d. binds to the operator to block RNA polymerase. e. binds to a silencer to reduce transcription rates. 49. The TATA box is a(n) a. sequence common to the promoter region of many genes. b. square-shaped sequence. c. enhancer consensus sequence. d. activator sequence necessary for proper translation. e. None of the above

10 Refer to the following list of enzymes to answer the following questions. The answers may be used once, more than once, or not at all a. helicase b. gyrase c. ligase d. DNA polymerase e. Primase 50. enhances separation of DNA strands during replication a. b. c. d. e 51. covalently connects segments of DNA 52. synthesizes short segments of RNA a. b. c. d. e 53. The strands that make up DNA are anti-parallel. This means that a. the twisting nature of DNA creates nonparallel strands. b. the 5 to 3 direction of one strand runs counter to the 5 to 3 direction of the other strand. c. base pairings create unequal spacing between the two DNA strands. d. one strand is positively charged while the other is negatively charged. e. the chromosomes are circular in shape. 54. A new DNA strand only elongates in the 5 to 3 direction because a. DNA polymerase begins adding nucleotides at the 5 end. b. Okazaki fragments prevent elongation in the 3 to 5 direction. c. the polarity of the DNA molecule prevents addition of nucleotides at the 3 end. d. replication must progress toward the replication fork. e. DNA polymerase adds nucleotides only to the free 3 end.