BIL 255 EXAM 2 ANSWERS

50. Which of the following molecules of RNA would you predict to be the most likely to fold into a specific structure as a result of intramolecular base-pairing? A) 5´-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3´ B) 5´-UGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUGUG-3´ C) 5´-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA-3´ D) 5´-GGAAAAGGAGAUGGGCAAGGGGAAAAGGAGAUGGGCAAGG-3´

A) 5´-CCCUAAAAAAAAAAAAAAAAUUUUUUUUUUUUUUUUAGGG-3´

9. The citric acid cycle is a critical sequence of reactions for energy production, which take place in the matrix of the mitochondria. The reaction cycle requires materials from the cytosol to be converted into acetyl CoA, which represents the starting point of a new cycle. Which of the following statements about acetyl CoA is TRUE? A) Amino acids can be converted into acetyl CoA. B) Pyruvate is converted into acetyl CoA in the cytosol. C) Triacylglycerol molecules are transported into the mitochondrial matrix and cleaved by lipases to produce acetyl CoA. D) Oxaloacetate is converted directly into acetyl CoA to feed the citric acid cycle.

A) Amino acids can be converted into acetyl CoA.

43. The repair of mismatched base pairs or damaged nucleotides in a DNA strand requires a multistep process. Which choice below describes the known sequence of events in this process? A) DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase. B) DNA repair polymerase simultaneously removes bases ahead of it and polymerizes the correct sequence behind it as it moves along the template. DNA ligase seals the nicks in the repaired strand. C) DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by an exonuclease, and the gap is repaired by DNA ligase. D) A nick in the DNA is recognized, DNA repair proteins switch out the wrong base and insert th

A) DNA damage is recognized, the newly synthesized strand is identified by an existing nick in the backbone, a segment of the new strand is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase.

55.Genes in eukaryotic cells often have intronic sequences coded for within the DNA. These sequences are ultimately not translated into proteins. Why? A) Intronic sequences are removed from RNA molecules by the spliceosome, which works in the nucleus. B) Introns are not transcribed by RNA polymerase. C) Introns are removed by catalytic RNAs in the cytoplasm. D) The ribosome will skip over intron sequences when translating RNA into protein.

A) Intronic sequences are removed from RNA molecules by the spliceosome, which works in the nucleus.

7. What purpose does the phosphorylation of glucose to glucose 6-phosphate by the enzyme hexokinase serve as the first step in glycolysis? A) It helps drive the uptake of glucose from outside the cell. B) It generates a high-energy phosphate bond. C) It converts ATP to a more useful form. D) It enables the glucose 6-phosphate to be recognized by phosphofructokinase, the next enzyme in the glycolytic pathway.

A) It helps drive the uptake of glucose from outside the cell.

4. The conversion of glyceraldehyde 3-phosphate to 1,3 bisphosphoglycerate in step 6 of glycolysis generates a "high- energy" phosphoanhydride bond. Which of the following BEST describes what happens to that bond in step 7? A) It is hydrolyzed to drive the formation of ATP. B) It is hydrolyzed to drive the formation of NADH. C) It is hydrolyzed to generate pyruvate. D) It is oxidized to CO2.

A) It is hydrolyzed to drive the formation of ATP.

44. Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the cytosine in the sequence TCAT is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication? A) TTAT B) TUAT C) TGAT D) TAAT

A) TTAT

11. In the final stage of the oxidation of food molecules, a gradient of protons is formed across the inner mitochondrial membrane, which is normally impermeable to protons. If cells were exposed to an agent that causes the membrane to become freely permeable to protons, which of the following effects would you expect to observe? A) The ratio of ATP to ADP in the cytoplasm would fall. B) NADH would build up. C) Carbon dioxide production would cease. D) The consumption of oxygen would fall.

A) The ratio of ATP to ADP in the cytoplasm would fall.

52. Which of the following does not occur before a eukaryotic mRNA is exported from the nucleus? A) The ribosome binds to the mRNA. B) The mRNA is polyadenylated at its 3´ end. C) A guanine nucleotide with a methyl group is added to the 5´ end of the mRNA. D) RNA polymerase dissociates.

A) The ribosome binds to the mRNA.

37. What part of the DNA replication process would be most directly affected if a strain of bacteria lacking primase were used to make the cell extracts? A) initiation of DNA synthesis B) Okazaki fragment synthesis C) leading-strand elongation D) lagging-strand completion

A) initiation of DNA synthesis

38. What part of the DNA replication process would be most directly affected if a strain of bacteria lacking helicase were used to make the cell extracts? A) initiation of DNA synthesis B) Okazaki fragment synthesis C) leading-strand elongation D) lagging-strand completion

A) initiation of DNA synthesis

32. Methylation and acetylation are common changes made to histone H3, and the specific combination of these changes is sometimes referred to as the "histone code." Which of the following patterns will probably lead to gene silencing? A) lysine 9 methylation B) lysine 4 methylation and lysine 9 acetylation C) lysine 14 acetylation D) lysine 9 acetylation and lysine 14 acetylation

A) lysine 9 methylation

48. Nonhomologous end joining can result in all but which of the following? A) the recovery of lost nucleotides on a damaged DNA strand B) the interruption of gene expression C) loss of nucleotides at the site of repair D) translocations of DNA fragments to an entirely different chromosome

A) the recovery of lost nucleotides on a damaged DNA strand

10. In step 4 of the citric acid cycle, the reduction of NAD+ to NADH is coupled to the generation of CO2 and the formation of a high-energy thioester bond. The energy of the thioester bond is harnessed in step 5. What is the energy used for? A) to generate a molecule of GTP B) to generate a molecule of ATP C) to generate a proton gradient D) to generate a molecule of NADH`

A) to generate a molecule of GTP

19. The mitochondrial ATP synthase consists of several different protein subunits. Which subunit binds to ADP + Pi and catalyzes the synthesis of ATP as a result of a conformational change? A) transmembrane H+ carrier B) F1 ATPase head C) peripheral stalk D) central stalk

B) F1 ATPase head

54. Which of the following statements about RNA splicing is FALSE? A) Conventional introns are not found in bacterial genes. B) For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene. C) Small RNA molecules in the nucleus perform the splicing reactions necessary for the removal of introns. D) Splicing occurs after the 5´ cap has been added to the end of the primary transcript.

B) For a gene to function properly, every exon must be removed from the primary transcript in the same fashion on every mRNA molecule produced from the same gene.

5. Steps 7 and 10 of glycolysis result in substrate-level phosphorylation. Which of the following best describes this process? A) ATP is being hydrolyzed to phosphorylate the substrate. B) The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP. C) Two successive phosphates are transferred, first to AMP, then to ADP, finally forming ATP. D) The substrate is hydrolyzed using ATP as an energy source.

B) The energy derived from substrate oxidation is coupled to the conversion of ADP to ATP.

34. Fred Griffith studied two strains of Streptococcus pneumonia, one that causes a lethal infection when injected into mice, and a second that is harmless. He observed that pathogenic bacteria that have been killed by heating can no longer cause an infection. But when these heat-killed bacteria are mixed with live, harmless bacteria, this mixture is capable of infecting and killing a mouse. What did Griffith conclude from this experiment? A) The infectious strain cannot killed by heating. B) The heat-killed pathogenic bacteria "transformed" the harmless strain into a lethal one. C) The harmless strain somehow revived the heat-killed pathogenic bacteria. D) The mice had lost their immunity to infection with S. pneumoniae.

B) The heat-killed pathogenic bacteria "transformed" the harmless strain into a lethal one.

18. Which of the following statements is TRUE? A) The NADH dehydrogenase complex does not pump protons across the membrane. B) The pH in the mitochondrial matrix is higher than the pH in the intermembrane space. C) The proton concentration gradient and the membrane potential across the inner mitochondrial membrane tend to work against each other in driving protons from the intermembrane space into the matrix. D) The difference in proton concentration across the inner mitochondrial membrane has a much larger effect than the membrane potential on the total proton-motive force.

B) The pH in the mitochondrial matrix is higher than the pH in the intermembrane space.

8. The first energy-generating steps in glycolysis begin when glyceraldehyde 3-phosphate undergoes an energetically favorable reaction in which it is simultaneously oxidized and phosphorylated by the enzyme glyceraldehyde 3-phosphate dehydrogenase to form 1,3-bisphosphoglycerate, with the accompanying conversion of NAD+ to NADH. In a second energetically favorable reaction catalyzed by a second enzyme, the 1,3-bisphosphoglycerate is then converted to 3- phosphoglycerate, with the accompanying conversion of ADP to ATP. Which of the following statements is TRUE about this reaction? A) The reaction glyceraldehyde 3-phosphate ® 1,3-bisphosphoglycerate should be inhibited when levels of NADH fall. B) The ∆G° for the oxidation of the aldehyde group on glyceraldehyde 3-phosphate to form a carboxylic acid is more negative than the ∆G° for ATP hydrolysis. C) The energy stored in the phosphate bond of glyceraldehyde

B) The ∆G° for the oxidation of the aldehyde group on glyceraldehyde 3-phosphate to form a carboxylic acid is more negative than the ∆G° for ATP hydrolysis.

39. The DNA duplex consists of two long covalent polymers wrapped around each other many times over their entire length. The separation of the DNA strands for replication causes the strands to be "overwound" in front of the replication fork. How does the cell relieve the torsional stress created along the DNA duplex during replication? A) Nothing needs to be done because the two strands will be separated after replication is complete. B) Topoisomerases break the covalent bonds of the backbone, allowing the local unwinding of DNA ahead of the replication fork. C) Helicase unwinds the DNA and rewinds it after replication is complete. D) DNA repair enzymes remove torsional stress as they replace incorrectly paired bases.

B) Topoisomerases break the covalent bonds of the backbone, allowing the local unwinding of DNA ahead of the replication fork.

46. Sickle-cell anemia is an example of an inherited disease. Individuals with this disorder have misshapen (sickle-shaped) red blood cells caused by a change in the sequence of the b-globin gene. What is the nature of the change? A) chromosome loss B) base-pair change C) gene duplication D) base-pair insertion

B) base-pair change

31. The N-terminal tail of histone H3 can be extensively modified, and depending on the number, location, and combination of these modifications, these changes may promote the formation of heterochromatin. What is the result of heterochromatin formation? A) increase in gene expression B) gene silencing C) recruitment of remodeling complexes D) displacement of histone H1

B) gene silencing

2. Glycolysis generates more stored energy than it expends. What is the net number of activated carrier molecules produced in this process (number and type of molecules produced minus the number of those molecules used as input)? A) 6 ATP, 2 NADH B) 4 ATP, 4 NADH C) 2 ATP, 2 NADH D) 4 ATP, 2 NADH

C) 2 ATP, 2 NADH

26. Which DNA base pair is represented in the figure? A) A-T B) T-A C) G-C D) C-G

C) G-C

Which of the following statements is TRUE? A) The two genes must be transcribed into RNA using the same strand of DNA. B) If gene A is transcribed in a cell, gene B cannot be transcribed. C) Gene A and gene B can be transcribed at different rates, producing different amounts of RNA within the same cell. D) If gene A is transcribed in a cell, gene B must be transcribed.

C) Gene A and gene B can be transcribed at different rates, producing different amounts of RNA within the same cell.

17. During Stage 2 of oxidative phosphorylation, ATP synthesis is powered by movement of ______ ions through the ______. A) H+; H+ pump B) OH- ; porin complex C) H+; ATP synthase D) elections; electron-transport chain

C) H+; ATP synthase

29. The core histones are small, basic proteins that have a globular domain at the C-terminus and a long, extended conformation at the N-terminus. Which of the following is NOT true of the N-terminal "tail" of these histones? A) It is subject to covalent modifications. B) It extends out of the nucleosome core. C) It binds to DNA in a sequence-specific manner. D) It helps DNA pack tightly.

C) It binds to DNA in a sequence-specific manner.

16. What is the final result of the electron transfers in Stage 1 of the membrane-based processes that drive ATP synthesis in mitochondria? A) OH- is oxidized to O2 B) pyruvate is oxidized to CO2 C) O2 is reduced to H2O D) H- is converted to H2

C) O2 is reduced to H2O

23. If you add a compound to illuminated chloroplasts that inhibits the NADP+ reductase, NADPH generation ceases, as expected. However, ferredoxin does not accumulate in the reduced form because it is able to donate its electrons not only to NADP+ (via NADP+ reductase) but also back to the cytochrome b6-f complex. Thus, in the presence of the compound, a "cyclic" form of photosynthesis occurs in which electrons flow in a circle from ferredoxin, to the cytochrome b6-f complex, to plastocyanin, to photosystem I, to ferredoxin. What will happen if you now also inhibit photosystem II? A) Less ATP will be generated per photon absorbed. B) ATP synthesis will cease. C) Plastoquinone will accumulate in the oxidized form. D) Plastocyanin will accumulate in the oxidized form.

C) Plastoquinone will accumulate in the oxidized form.

45. Several members of the same family were diagnosed with the same kind of cancer when they were unusually young. Which one of the following is the most likely explanation for this phenomenon? It is possible that the individuals with the cancer have inherited A) a cancer-causing gene that suffered a mutation in an ancestor's somatic cells. B) a mutation in a gene required for DNA synthesis. C) a mutation in a gene required for mismatch repair. D) a mutation in a gene required for the synthesis of purine nucleotides.

C) a mutation in a gene required for mismatch repair.

33. You are a virologist interested in studying the evolution of viral genomes. You are studying two newly isolated viral strains and have sequenced their genomes. You find that the genome of strain 1 contains 25% A, 55% G, 20% C, and 10% T. You report that you have isolated a virus with a single-stranded DNA genome. Based on what evidence can you make this conclusion? A) because single-stranded genomes always have a large percentage of purines B) by using the formula G - A = C + T C) because double-stranded genomes have equal amounts of A and T D) because single-stranded genomes have a higher rate of mutation

C) because double-stranded genomes have equal amounts of A and T

3. Which of the following steps or processes in aerobic respiration include the production of carbon dioxide? A) breakdown of glycogen B) glycolysis C) conversion of pyruvate to acetyl CoA D) oxidative phosphorylation

C) conversion of pyruvate to acetyl CoA

1. The advantage to the cell of the gradual oxidation of glucose during cellular respiration compared with its combustion to CO2 and H2O in a single step is that A) more free energy is released for a given amount of glucose oxidized. B) no energy is lost as heat. C) energy can be extracted in usable amounts. D) more CO2 is produced for a given amount of glucose oxidized.

C) energy can be extracted in usable amounts.

13. Which of the following compounds will NOT support the growth of animal cells when used as the major source of carbon in food, but will support the growth of nonphotosynthetic bacteria? A) pyruvate B) glucose C) fatty acids D) fructose

C) fatty acids

20. Bongkrekic acid is an antibiotic that inhibits the ATP/ADP transport protein in the inner mitochondrial membrane. Which of the following will allow electron transport to occur in mitochondria treated with bongkrekic acid? A) placing the mitochondria in anaerobic conditions B) adding FADH2 C) making the inner membrane permeable to protons D) inhibiting the ATP synthase

C) making the inner membrane permeable to protons

30. Although the chromatin structure of interphase and mitotic chromosomes is very compact, DNA-binding proteins and protein complexes must be able to gain access to the DNA molecule. Chromatin-remodeling complexes provide this access by A) recruiting other enzymes. B) modifying the N-terminal tails of core histones. C) using the energy of ATP hydrolysis to move nucleosomes. D) denaturing the DNA by interfering with hydrogen-bonding between base pairs.

C) using the energy of ATP hydrolysis to move nucleosomes.

25. Which of the following DNA strands can form a DNA duplex by pairing with itself at each position? A) 5´-AAGCCGAA-3´ B) 5´-AAGCCGTT-3´ C) 5´-AAGCGCAA-3´ D) 5´-AAGCGCTT-3´

D) 5´-AAGCGCTT-3´

12. Step 3 in glycolysis requires the activity of phosphofructokinase to convert fructose 6-phosphate into fructose 1,6- bisphosphate. Which of the following molecules is an allosteric inhibitor of this enzyme? A) Pi B) AMP C) ADP D) ATP

D) ATP

14. Which of the following is NOT part of the process known as "oxidative phosphorylation"? A) Molecular oxygen serves as a final electron acceptor. B) FADH2 and NADH become oxidized as they transfer a pair of electrons to the electron-transport chain. C) The electron carriers in the electron-transport chain toggle between reduced and oxidized states as electrons are passed along. D) ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

D) ATP molecules are produced in the cytosol as glucose is converted into pyruvate.

28. Which of the following questions would NOT be answered by using karyotyping? A) Is the individual genetically female or male? B) Do any of the chromosomes contain pieces that belong to other chromosomes? C) Does the individual have an extra chromosome? D) Do any chromosomes contain point mutations

D) Do any chromosomes contain point mutations

24. Which of the following statements about the possible fates of glyceraldehyde 3-phosphate is FALSE? A) It can be exported from the chloroplast to the cytosol for conversion into sucrose. B) It can be used to make starch, which is stored inside the stroma of the chloroplast. C) It can be used as a precursor for fatty acid synthesis and stored as fat droplets in the stroma. D) It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron transport chain

D) It can be transported into the thylakoid space for use as a secondary electron acceptor downstream of the electron transport chain

36. You have discovered an "Exo- " mutant form of DNA polymerase in which the 3´-to-5´ exonuclease (proofreading) function has been destroyed but the ability to join nucleotides together is unchanged. Which of the following properties do you expect the mutant polymerase to have? A) It will polymerize in both the 5´-to-3´ direction and the 3´-to-5´ direction. B) It will polymerize more slowly than the normal Exo+ polymerase. C) It will fall off the template more frequently than the normal Exo+ polymerase. D) It will be more likely to generate mismatched base pairs.

D) It will be more likely to generate mismatched base pairs.

41. You are examining the DNA sequences that code for the enzyme phosphofructokinase in skinks and Komodo dragons. You notice that the coding sequence that actually directs the sequence of amino acids in the enzyme is very similar in the two organisms but that the surrounding sequences vary quite a bit. What is the most likely explanation for this? A) Coding sequences are repaired more efficiently. B) Coding sequences are replicated more accurately. C) Coding sequences are packaged more tightly in the chromosomes to protect them from DNA damage. D) Mutations in coding sequences are more likely to be deleterious to the organism than mutations in noncoding sequences.

D) Mutations in coding sequences are more likely to be deleterious to the organism than mutations in noncoding sequences.

22. Stage 2 of photosynthesis, sometimes referred to as the dark reactions, involves the reduction of CO2 to produce organic compounds such as sucrose. What cofactor is the electron donor for carbon fixation? A) H2O B) NADH C) FADH2 D) NADPH

D) NADPH

40. Telomeres serve as caps protecting the ends of linear chromosomes. Which of the following is FALSE regarding the replication of telomeric sequences? A) The lagging-strand telomeres are not completely replicated by DNA polymerase. B) Telomeres are made of repeating sequences. C) Additional repeated sequences are added to the template strand. D) The leading strand doubles back on itself to form a primer for the lagging strand.

D) The leading strand doubles back on itself to form a primer for the lagging strand.

35. Which of the following statements correctly explains what it means for DNA replication to be bidirectional? A) The replication fork can open or close, depending on the conditions. B) The DNA replication machinery can move in either direction on the template strand. C) Replication-fork movement can switch directions when the fork converges on another replication fork. D) The replication forks formed at the origin move in opposite directions.

D) The replication forks formed at the origin move in opposite directions.

51. Which of the following might decrease the transcription of only one specific gene in a bacterial cell? A) a decrease in the amount of sigma factor B) a decrease in the amount of RNA polymerase C) a mutation that introduced a stop codon into the DNA that precedes the gene's coding sequence D) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site

D) a mutation that introduced extensive sequence changes into the DNA that precedes the gene's transcription start site

15. Electron transport is coupled to ATP synthesis in mitochondria, in chloroplasts, and in the thermophilic bacterium Methanococcus. Which of the following is likely to affect the coupling of electron transport to ATP synthesis in ALL of these systems? A) a potent inhibitor of cytochrome c oxidase B) the removal of oxygen C) the absence of light D) an ADP analog that inhibits ATP synthase

D) an ADP analog that inhibits ATP synthase

27. The complete set of information in an organism's DNA is called its A) genetic code. B) coding sequence. C) gene. D) genome.

D) genome.

6. Which of the following processes do NOT take place in the mitochondria? A) citric acid cycle B) conversion of pyruvate to activated acetyl groups C) oxidation of fatty acids to acetyl CoA D) glycogen breakdown

D) glycogen breakdown

53. Total nucleic acids are extracted from a culture of yeast cells and are then mixed with resin beads to which the polynucleotide 5´-TTTTTTTTTTTTTTTTTTTTTTTTT-3´ has been covalently attached. After a short incubation, the beads are then extracted from the mixture. When you analyze the cellular nucleic acids that have stuck to the beads, which of the following is most abundant? A) DNA B) tRNA C) rRNA D) mRNA

D) mRNA

49. Transcription is similar to DNA replication in that A) an RNA transcript is synthesized discontinuously and the pieces are then joined together. B) it uses the same enzyme as that used to synthesize RNA primers during DNA replication. C) the newly synthesized RNA remains paired to the template DNA. D) nucleotide polymerization occurs only in the 5´-to-3´ direction.

D) nucleotide polymerization occurs only in the 5´-to-3´ direction.

21. Photosynthesis is a process that takes place in chloroplasts and uses light energy to generate high-energy electrons, which are passed along an electron-transport chain. Where are the proteins of the electron-transport chain located in chloroplasts? A) thylakoid space B) stroma C) inner membrane D) thylakoid membrane

D) thylakoid membrane