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Intro to Molecular Cell Biology Test Bank Chapter 6
The process of DNA replicaƟon requires that each of the parental DNA strands be used as a ____________ to produce a duplicate of the opposing strand. (a) catalyst (b) compeƟtor (c) template (d) copy - (c) template DNA replicaƟon is considered semiconservaƟve because __________________________________. (a) aŌer many rounds of DNA replicaƟon, the original DNA double helix is sƟll intact. (b) each daughter DNA molecule consists of two new strands copied form the parent (c) each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand. - (c) each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand The classic experiment conducted by Meselson and Stahl demonstrated that DNA replicaƟon is accomplished by employing a ______________ mechanism. - semiconservaƟve IniƟator proteins bind to replicaƟon origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relaƟve ease of strand separaƟon by iniƟator proteins? (a) replicaƟon origins are rich in A-T base pairs (b) the reacƟon can occur at room temperature (c) they only separate a few base pairs at a Ɵme (d) once opened, other porƟons of the DNA replicaƟon machinery bind to the origin - (b) the reacƟon can occur at room temperature If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of a fruit fly be replicated in only 3 minutes? (a) The fruit fly genome is smaller than E coli
(b) EukaryoƟc DNA polymerase synthesizes DNA at a much faster rate than prokaryoƟc (c) The nuclear membrane keeps the fruit fly DNA concentrated in one place in the cell, which increases the rate of polymerizaƟon (d) Fruit fly DNA contains more origins of replicaƟon than E coli DNA. - (d) Fruit fly DNA contains more origins of replicaƟon than E coli DNA True or false? When DNA is being replicated inside a cell, local heaƟng occurs, allowing the two strands to separate. - False. This is accomplished by iniƟated proteins binding at the origin of replicaƟon. True or false? DNA replicaƟon origins are typically rich in G-C base pairs. - They are rich in A-T base pairs which makes it easier for them to separate the strands because they are only held together by two hydrogen bonds True or false? Meselson and Stahl ruled out the dispersive model for DNA replicaƟon. - true True or false? DNA replicaƟon is a bidirecƟonal process that is iniƟated at mulƟple locaƟons among chromosomes in eukaryoƟc cells. - True How many replicaƟon forks are formed when an origin of replicaƟon is opened? - 2 How does the total number of replicaƟon origins in bacterial cells compare with the number of origins in human cells? - 1 versus 10, Which of the following statement correctly explains what it means for DNA replicaƟon to be bidirecƟonal? (a) The replicaƟon forks formed at the origin moved in opposite direcƟons. (b) the DNA replicaƟon machinery can move in either direcƟon on the template strand (c) The replicaƟon fork can either open or close depending on the condiƟon
What part of the DNA replicaƟon process would be most directly affected if a strain of bacteria lacking the exonuclease acƟvity of DNA polymerase were used to make the cell extracts? (a) iniƟaƟon of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongaƟon (d) lagging-strand compleƟon - (d) lagging strand compleƟon What part of the DNA replicaƟon process would be most directly affected if a strain of bacteria lacking helicase were used to make the cell extracts? (a) iniƟaƟon of DNA synthesis (b)Okazaki fragment synthesis (c) leading strand elongaƟon (d) lagging strand compleƟon - (a) inƟaƟon of DNA synthesis What part of the DNA replicaƟon process would be most directly affected if a strain of bacteria lacking single-strand binding protein were used to make the cell extracts? (a) iniƟaƟon of DNA synthesis (b) Okazaki fragment synthesis (c) leading strand elongaƟon (d) lagging strand compleƟon - (b) Okazaki fragment synthesis What part of the DNA replicaƟon process would be most directly affected if a strain of bacteria lacking DNA ligase were used? (a) iniƟaƟon of DNA synthesis (b) Okazaki fragment synthesis (c) leading strand elongaƟon (d) lagging strand compleƟon - (d) lagging strand compleƟon Which of the following statements is true about the newly synthesized strand of a human chromosome? (a) It was synthesized from mulƟple origins by a mixture of conƟnuous and disconƟnuous DNA synthesis.
(b) It was synthesized from a single origin solely by conƟnuous DNA synthesis. (c) It was synthesized from a single origin by a mixture of disconƟnuous and conƟnuous synthesis. - (a) It was synthesized from mulƟple origins by a mixture of conƟnuos and disconƟnuous DNA synthesis You have discovered an Exo mutant form of DNA polymerase in which the 3' to 5' exonuclease funcƟon has been destroyed but the ability to join nucleoƟdes together is unchanged. Which of the following properƟes do you expect the mutant polymerase to have? (a) It will be more likely to generate mismatched base pairs. (b) It will fall off the template more frequently than the normal. (c) It will polymerize more slowly (d) It will polymerize in both direcƟons - (a) It will be more likely to generate mismatched base pairs. A molecule of bacterial DNA introduced into a yeast cell is imported into the nucleus but fails to replicate with the yeast of DNA. Choose the protein or protein complex below that is most likely responsible for the failure to replicate bacterial DNA. (a) primase (b) helicase (c) DNA polymerase (d) iniƟator proteins - (d) iniƟator proteins True or false? Primase is needed to iniƟate DNA replicaƟon on both lagging and the leading strand. - True True or false? The sliding clamp is loaded once on each DNA strand where it remains associated unƟl replicaƟon is complete. - False. True or false? Telomerase is a DNA polymerase that carries its own RNA molecule to uses as a primer at the end of the lagging strand. - true
(d) If an incorrect base is added, it is unpaired before removal. - (b) The exonuclease acƟvity cleaves DNA in the '5-to-3' direcƟon. The DNA duplex consists of two long covalent polymers wrapped around each other many Ɵmes over their enƟre length. The separaƟon of DNA strands for replicaƟon causes the strands to be overwound in front of the replicaƟon fork. How does the cell relieve the torsional stress created along the DNA duplex during replicaƟon? (a) Nothing needs to be done because the two strands will be separated aŌer replicaƟon is complete. (b) Topoisomerases break the covalent bonds of the backbone allowing the local unwinding of DNA ahead of the replicaƟon fork. (c) Helicase unwinds the DNA and rewinds it aŌer replicaƟon is complete. (d) DNA repair enzymes remove 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 replicaƟon fork. Telomeres serve as caps at the ends of linear chromosomes. Which of the following is not true regarding the replicaƟon of telomeric sequences? (a) The lagging strand telomeres are not completely replicated by DNA polymerase. (b) Telomeres are made of repeaƟng sequences (c) AddiƟonal 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 Sickle-cell anemia is an inherited disease that causes a disorder where red blood cells are misshapen caused by a change in the sequence of the B-globin gene. What is the nature of this change? (a) chromosome loss (b) base-pair change (c) gene duplicaƟon (d) base-pair inserƟon - (b) base-pair change To what degree does the mismatch repair system decrease the error rate arising from DNA replicaƟon? (a) 2 fold
(b) 5 fold (c) 10 fold (d) 100 fold - (d) 100 fold Beside the distorƟon in the DNA backbone caused by a mismatched base pair, what addiƟonal mark is there on eukaryoƟc DNA to indicate which strand needs to be repaired? (a) a nick in the template strand (b) a chemical modificaƟon of the new strand (c) a nick in the new strand (d) a sequence gap in the new strand - (c) a nick in the new strand A pregnant mouse is exposed to high levels of a chemical. Many of the mice in her liter are deformed, but when they are interbred with another, all of their offspring are normal. Which two of the following statements could explain these results? (a) In the deformed mice, somaƟc cells but not germ cells were mutated (b) The original mouse's germ cells were mutated (c) In the deformed mice, germ cells but not somaƟc cells were mutated (d) The toxic chemical affects development but is not mutagenic. - (a) In the deformed mice, somaƟc cells but not germ cells were mutated. and (d) The toxic chemical affects development but it not mutagenic The repair of mismatched base pairs or damaged nucleoƟdes in a DNA strand requires a mulƟstep process. Which choice below describes the sequence of events in this process? (a) DNA damage is recognized, the newly synthesized strand is idenƟfied by an exisƟng nick in the backbone, a segment 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. - (a) DNA damage is recognized, the newly synthesized strand is idenƟfied by an exisƟng nick in the backbone, a segment is removed by repair proteins, the gap is filled by DNA polymerase, and the strand is sealed by DNA ligase.
SomeƟmes, chemical damage to DNA can occur just before DNA replicaƟon begins, not giving the repair system enough Ɵme to correct the error before it is duplicated. This gives rise to mutaƟon. If the adenosine in the sequence TCAT is depurinated and not repaired, what is the point mutaƟon you would observe aŌer this segment has undergone two rounds of replicaƟon? - TCT Which of the following statements is not an accurate statement about thymine dimers? (a) They can cause the DNA replicaƟon machinery to stall. (b) They are covalent links between thymidines on oppoiste DNA strands (c) Prolonged exposure to sunlight causes thymine dimers to form (d) Repair proteins recognize thymine dimers as a distorƟon in the DNA backbone - (b) They are covalent links between thymidines on opposite DNA strands True or false? Ionizing radiaƟon and oxidaƟve damage can cause DNA double-strand breaks. - True True or false? AŌer damaged DNA has been repaired, nicks in the phosphate backbone are maintained as a way to idenƟfy the strand that was repaired. - False True or false? DepurinaƟon of DNA is rare event that is caused by ultraviolet irradiaƟon. - False True or false? Nonhomologous end joining is a mechanism that ensures that DNA double strand breaks are repaired with a high degree of fidelity to the original DNA sequence. - False 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 most likely explanaƟon for this? It is possible that the individuals with cancer have ________________. (a) inherited a cancer causing gene that suffered mutaƟon in somaƟc cells (b) inherited a mutaƟon in a gene required for DNA synthesis (c) inherited a mutaƟon in a gene required for mismatch repair - (c) inherited a mutaƟon in a gene required for mismatch repair
Nonhomologous end joining is a process by which a double-stranded DNA end is joined ____________________________. (a) to a similar stretch of sequence on the complementary chromosome (b) aŌer repairing any mismatches (c) to the nearest available double stranded DNA end - (c) to the nearest available double stranded DNA end Nonhomologous end joining can result in all but which of the following? (a) the recovery of lost nucleoƟdes on a damaged DNA strand (b) the interrupƟon of gene expression (c) loss of nucleoƟdes - (a) the recovery of lost nucleoƟdes on a damaged DNA strand Which of the following is not neccessary for homologous recombinaƟon to occur? (a) 3' DNA strand overhangs (b) 5' DNA strand overhangs (c) a long stretch of sequence similarity (d) nucleases - (b) 5' strand overhangs In addiƟon to the repair of DNA double strand breaks, homogolous recombinaƟon is a mechanism for generaƟng geneƟc diversity by swapping segments of parental chromosomes. Which process does this swapping occur? (a) replicaƟon (b) DNA repair (c) meiosis (d) transportaƟon - (c) meiosis
