Deck 13: Dna Replication and Repair

Question 1

Cultured mammalian cells grown in thymidine for many generations were allowed to undergo replication in the presence of bromodeoxyuridine (BrdU),which replaces thymidine in DNA.After two rounds of replication,what would the DNA look like if replication were conservative?

A)All chromatids have one strand that contains BrdU and one strand that does not.
B)All chromatids have two strands that contain BrdU.
C)Half of the chromatids have two strands that contain BrdU and half of the chromatids have 2 strands lacking BrdU.
D)Both strands of each chromatid contain mixtures of BrdU and thymidine.
E)75% of the chromatids have two strands that contain BrdU and 25% of the chromatids have 1 strand lacking BrdU and 1 strand containing BrdU.

Answer 1

E

Question 2

Bacteria are grown in a medium containing ¹⁵NH₄Cl for a number of generations so that all of the DNA is made of fully "heavy" DNA.The bacteria are moved to a new medium and grown in ¹⁵NH₄Cl so that all new DNA will be light.After one generation time,what does the DNA look like?

A)All of the DNA is made of 2 "light" strands.
B)All of the DNA is made of 2 "heavy" strands.
C)All of the DNA is made of 1 "heavy" strand and 1 "light" strand.
D)Each strand is made of a mixture of "heavy" and "light" DNA,with each strand being between 75% and 100% "light".
E)Half of the DNA is made of 2 "light" strands and half of the DNA is made of 2 "heavy" strands.

Answer 2

C

Question 3

Cultured mammalian cells grown in thymidine for many generations were allowed to undergo replication in the presence of bromodeoxyuridine (BrdU),which replaces thymidine in DNA.After two rounds of replication,what does the DNA look like?

A)All chromatids have one strand that contains BrdU and one strand that does not.
B)All chromatids have two strands that contain BrdU.
C)Half of the chromatids have two strands that contain BrdU and half of the chromatids have 2 strands lacking BrdU.
D)Both strands of each chromatid contain mixtures of BrdU and thymidine.
E)Half of the chromatids have two strands that contain BrdU and half of the chromatids have 1 strand lacking BrdU and one strand containing BrdU.

Answer 3

E

Question 4

In replicating bacterial chromosomes,where does replication terminate?

A)at the origin
B)across the circular chromosome from the origin
C)at random locations around the circle
D)one quarter of the way around the DNA circle from the origin
E)near Arnold

Question 5

Why is an intact,linear double helix an ineffective template for DNA polymerase?

A)It has a 3'-hydroxyl group,but lacks a template.
B)It lacks a 3'-hydroxyl group,but has a template.
C)It lacks a 3'-hydroxyl group and a template.
D)It has a 3'-hydroxyl group and has a template.
E)It lacks a 5'-hydroxyl group and has a template.

Question 6

In early experiments with DNA polymerase I,what evidence convinced investigators that the original unlabeled DNA in the reaction mixture served as the template for the newly made DNA?

A)The new DNA had the same base composition as the original unlabeled DNA.
B)The new DNA had a variable base composition.
C)The new DNA had a triple helix.
D)The new DNA and the old DNA were made of the same elements.
E)The new DNA was equally stable.

Question 7

The replication fork generates _______ supercoils in the _______ portion of the DNA molecule.

A)negative,replicated
B)positive,replicated
C)neutral,unreplicated
D)positive,unreplicated
E)negative,unreplicated

Question 8

Who was the first to suggest semiconservative replication?

A)Meselson and Stahl
B)Hershey and Chase
C)Watson and Crick
D)Avery,McCarty and MacLeod
E)Darwin and Wallace

Question 9

Which type of replication results in 2 duplexes made of one parental strand and one newly synthesized strand?

A)semiconservative replication
B)conservative replication
C)dispersive replication
D)incisive replication
E)reservative replication

Question 10

Replication moves outward from the origin in ________ direction(s)and is said to be ________.

A)both,unidirectional
B)both,bidirectional
C)one,bidirectional
D)unique,unidirectional
E)one,unidirectional

Question 11

Who was the first to purify an enzyme from bacterial extracts that could incorporate DNA precursors into a polymer?

A)Arthur Kornberg
B)James Watson
C)Francis Crick
D)Jacques Monod
E)Joel B.Piperberg (I wish!)

Question 12

Cultured mammalian cells grown in thymidine for many generations were allowed to undergo replication in the presence of bromodeoxyuridine (BrdU),which replaces thymidine in DNA.After one round of replication,what would the DNA look like if replication were dispersive?

A)All chromatids have one strand that contains BrdU and one strand that does not.
B)All chromatids have two strands that contain BrdU.
C)Half of the chromatids have two strands that contain BrdU and half of the chromatids have 2 strands lacking BrdU.
D)Both strands of each chromatid contain mixtures of BrdU and thymidine.
E)All chromatids lack BrdU.

Question 13

The specific site on the bacterial chromosome at which replication begins is called the ________.

A)beginning
B)origin
C)initiation site
D)initiator
E)replicon

Question 14

Cultured mammalian cells grown in thymidine for many generations were allowed to undergo replication in the presence of bromodeoxyuridine (BrdU),which replaces thymidine in DNA.After one round of replication,what does the DNA look like?

A)All chromatids have one strand that contains BrdU and one strand that contains thymidine.
B)All chromatids have two strands that contain BrdU.
C)Half of the chromatids have two strands that contain BrdU and half of the chromatids have 2 strands lacking BrdU.
D)Both of the strands of each chromatid contain mixtures of BrdU and thymidine.
E)All chromatids lack BrdU.

Question 15

Bacteria are grown in a medium containing ¹⁵NH₄Cl for a number of generations so that all of the DNA is made of fully "heavy" DNA.The bacteria are moved to a new medium and grown in ¹⁴NH₄Cl so that all new DNA will be "light".If replication were dispersive,what would the DNA look like after two generation times.

A)All of the DNA is made of 2 "light" strands.
B)Half of the DNA is made of 2 "light" strands and half of the DNA is made of 1 "light" strand and 1 "heavy" strand.
C)All of the DNA is made of 1 "heavy" strand and 1 "light" strand.
D)Each strand is made of a mixture of "heavy" and "light" DNA,with each strand being between 75% and 100% "light".
E)75% of the DNA is made of 2 "light" strands and 25% of the DNA is made of 2 "heavy" strands.

Question 16

What happens to DNA (circular DNA or linear DNA that is not free to rotate)when it becomes overwound?

A)It becomes negatively supercoiled.
B)It breaks into a number of fragments.
C)It becomes positively supercoiled.
D)It stretches.
E)Its mass decreases.

Question 17

Where is DNA gyrase normally positioned as it changes positively supercoiled DNA into negatively supercoiled DNA in the replicating circular,bacterial chromosome?

A)It is permanently located at the origin.
B)It travels along the DNA behind the replication fork.
C)It travels along the DNA ahead of the replication fork.
D)It travels along the DNA at the replication fork as part of the replisome.
E)It is permanently located at the termination site of replication.

Question 18

What supplies the energy that drives the relief of mechanical strain by DNA gyrase?

A)condensation of ATP
B)condensation of GTP
C)hydrolysis of ATP
D)hydrolysis of GTP
E)a proton gradient

Question 19

What type of replication results in the integrity of both parental strands being disrupted? The new duplex strands are made of both old and new DNA.Neither the parental strands nor the parental duplex is preserved.

A)semiconservative replication
B)conservative replication
C)dispersive replication
D)incisive replication
E)reservative replication

Question 20

Bacteria are grown in a medium containing ¹⁵NH₄Cl for a number of generations so that all of the DNA is made of fully "heavy" DNA.The bacteria are moved to a new medium and grown in ¹⁵NH₄Cl so that all new DNA will be "light".If replication were conservative,what would the DNA look like after two generation times.

A)All of the DNA is made of 2 "light" strands.
B)Half of the DNA is made of 2 "light" strands and half of the DNA is made of 1 "light" strand and 1 "heavy" strand.
C)All of the DNA is made of 1 "heavy" strand and 1 "light" strand.
D)Each strand is made of a mixture of "heavy" and "light" DNA with each strand being between 75% and 100% "light".
E)75% of the DNA is made of 2 "light" strands and 25% of the DNA is made of 2 "heavy" strands.

Question 21

In bacteria,a _______ is formed when a ________ associates transiently with a _______.

A)primosome,helicase,DNA polymerase
B)primosome,helicase,primase
C)ribosome,helicase,primase
D)helicosome,primosome,DNA polymerase
E)primosome,helicase,DNA ligase

Question 22

How can the replication of both DNA strands by two tethered polymerases be accomplished when the template strands run in opposite directions?

A)One of the enzymes polymerizes DNA in the 3'->5' direction.
B)The DNA of the lagging strand loops back on itself so it has same orientation as the leading strand template.
C)The DNA of the leading strand loops back on itself so it has same orientation as the lagging strand template.
D)The lagging strand is broken and then rejoined regularly to allow simultaneous synthesis.
E)It just is.

Question 23

Which DNA polymerase in bacteria is mostly involved in DNA repair to correct damaged DNA sections and removes RNA primers at the 5' ends of Okazaki fragments,replacing them with DNA?

A)DNA polymerase I
B)DNA polymerase II
C)DNA polymerase III
D)DNA polymerase IV
E)both DNA polymerase I and DNA polymerase III

Question 24

What proteins bind selectively to single-stranded DNA and are responsible for keeping it extended and preventing it from being rewound?

A)DNA helicase
B)DNA gyrase
C)single-stranded DNA binding (SSB)proteins
D)ATPase
E)DNA unwindase

Question 25

Which of the following may be a further advantage of using RNA primers during initiation of a strand in replication?

A)Using primers may decrease mistakes; such errors as mismatched bases are more likely during initiation than elongation,and the use of a short,removable RNA segment avoids inclusion of mismatched bases.
B)Using primers is faster.
C)The RNA of the primers is more stable.
D)The RNA of the primers is more likely to lead to changes in base sequence,which enhances the rate of mutation and thus evolution.
E)The RNA of the primers allows more efficient packing of the chromosomes after its removal.

Question 26

All DNA polymerases lay down nucleotides in a ______ direction and move along the template in a _______ direction.

A)3'->5',5'->3'
B)N->C.C->N
C)5'->3',3'->5'
D)C->N,N->C
E)N->C,5'->3'

Question 27

Since one strand of DNA is synthesized continuously during replication and the other is made discontinuously,replication is said to be ___________.

A)continuous
B)hemicontinuous
C)discontinuous
D)semidiscontinuous
E)semicontinuous

Question 28

The DNA strand growing toward the replication fork grows ______ in a 5'->3' direction as the replication fork advances and is called the ________.

A)continuously,leading strand
B)discontinuously,lagging strand
C)continuously,lagging strand
D)discontinuously,leading strand
E)steadfastly,forthright strand

Question 29

During replication,DNA is constructed in small segments called ________ that are rapidly linked to longer pieces of DNA synthesized earlier.

A)Watson fragments
B)Tokyo fragments
C)Osaka fragments
D)Okazaki fragments
E)Ouabain fragments

Question 30

The enzyme that joins the small fragments of the lagging strand together into a continuous strand is called _______.

A)DNA gyrase
B)DNA ligase
C)DNA polymerase
D)primase
E)deoxyribonuclease

Question 31

The RNA primers that initiate replication are subsequently _____ and the resulting gap in the strand is _______ DNA and then sealed by _______.

A)filled in,removed by,DNA ligase
B)removed,filled in with,DNA ligase
C)removed,filled in with,RNA ligase
D)chemically altered to DNA,excised,DNA ligase
E)chemically altered to DNA,filled in with,DNA ligase

Question 32

The _______ strand fragment grows away from the replication fork toward the ___- end of the previously synthesized fragment to which it is subsequently linked.

A)leading,5'
B)lagging,5'
C)leading,3'
D)lagging,3'
E)lagging,N-terminal

Question 33

Where is the DnaB helicase first loaded onto the DNA?

A)at the replication terminator site
B)at the replication origin
C)at random locations through the circular chromosome
D)at the operator
E)at the promoter

Question 34

Why is a single-stranded,circular DNA an ineffective template for DNA polymerase?

A)It has a 3'-hydroxyl group,but lacks a template.
B)It lacks a 3'-hydroxyl group,but has a template.
C)It lacks a 3'-hydroxyl group and a template.
D)It has a 3'-hydroxyl group and has a template.
E)It lacks a 5'-hydroxyl group and has a template.

Question 35

As replication proceeds,the lagging strand template of the DNA is looped back on itself so that it has the same orientation as the leading strand template; the looping DNA repeatedly grows and shortens during lagging strand replication.This model is often referred to as the _________.

A)telescope model
B)extension model
C)trombone model
D)French horn model
E)piccolo model

Question 36

Which DNA polymerase in bacteria synthesizes DNA strands during replication and forms part of a complex that serves as a large replication machine?

A)DNA polymerase I
B)DNA polymerase II
C)DNA polymerase III
D)DNA polymerase IV
E)both DNA polymerase I and DNA polymerase III

Question 37

What discovery suggested the presence of other DNA polymerases in bacteria besides the Kornberg DNA polymerase enzyme?

A)Kornberg DNA polymerase mutants died.
B)Kornberg DNA polymerase mutants grew much more slowly.
C)Mutants with <1% of the normal Kornberg DNA polymerase enzyme activity multiplied at a normal rate.
D)Mutants with <1% of the normal Kornberg DNA polymerase enzyme activity multiplied at a low rate.
E)Kornberg DNA polymerase mutants reproduced much faster than normal bacteria.

Question 38

Strand initiation during replication is carried out by an enzyme that makes a short RNA molecule that is used as a primer; the enzyme is a distinct type of RNA polymerase,called _______.

A)RNA gyrase
B)RNA ligase
C)ribonuclease
D)primase
E)deoxyribonuclease

Question 39

How does DNA polymerase III move from one site on the lagging strand template to a site closer to replication fork?

A)It hitches a ride with the DNA polymerase that is moving that way along the leading strand template.
B)It hitches a ride with the DNA polymerase that is moving that way along the lagging strand template.
C)It moves by itself like a tiny molecular motor.
D)It transports from the earlier Okazaki fragment to the later Okazaki fragment.
E)It is moved toward the replication fork by a complex of proteins called the transportosome.

Question 40

_________ are DNA unwinding enzymes that unwind the DNA in a reaction using the energy from ________ to move along one of the DNA strands,breaking the _______ holding the two strands together.

A)DNA helicases,ATP dehydration,disulfide linkages
B)DNA gyrases,ATP hydrolysis,H bonds
C)DNA helicases,ATP hydrolysis,3'-5'-phosphodiester linkages
D)DNA helicases,ATP hydrolysis,H bonds
E)DNA gyrases,ATP dehydration,H bonds

Question 41

Which eukaryotic DNA polymerase replicates mitochondrial DNA and does not appear to be involved in nuclear DNA replication?

A)polymerase $\gamma$
B)polymerase $\delta$
C)polymerase $\varepsilon$
D)polymerase $\beta$
E)polymerase $\alpha$

Question 42

What is responsible for joining the last deoxyribonucleotide added during RNA primer digestion and the 5' end of the previously synthesized and adjacent DNA fragment?

A)DNA polymerase I
B)DNA polymerase III
C)DNA ligase
D)the holoenzyme
E)DNA gyrase

Question 43

The collection of proteins in eukaryotes that forms the replicative complex is known as the __________.

A)replicand
B)replicon
C)replisome
D)replimere
E)polymerizer

Question 44

The small portions in which eukaryotic cells replicate their genomes are called _______.

A)replicants
B)replicons
C)repliants
D)replicosomes
E)tracts

Question 45

At what stage of the cell cycle do the key protein kinases,like cyclin-dependent kinase become activated?

A)right after mitosis
B)right before mitosis
C)just before the start of S phase
D)in the middle of the G2 phase
E)in the G0 phase

Question 46

What is the mechanism of action of the anti-HIV drug AZT?

A)it causes double-strand DNA breaks
B)it inhibits DNA synthesis by reverse transcriptase
C)it prevents transcription in infected cells
D)it blocks the active site of DNA ligase
E)it prevents viral entry into cells

Question 47

What technique was used in the discovery of the existence in eukaryotic cells of replicons,a discovery in which single DNA molecules were shown to be replicated simultaneously at several sites along their length?

A)scanning electron microscopy
B)confocal laser scanning microscopy
C)autoradiography
D)polyacrylamide gel electrophoresis
E)isoelectric focusing

Question 48

DNA sequences comprising the yeast origin of replication can be removed from yeast cells and inserted into bacterial DNA molecules.Because these sequences promote replication of the DNA in which they are contained,they are referred to as __________.

A)polygamous replicating sequences
B)autonomous replicating sequences
C)analogous replicating sequences
D)ARSs
E)both autonomous replicating sequences and ARSs

Question 49

Which eukaryotic DNA polymerase functions in DNA repair,but does not appear to be involved in nuclear DNA replication?

A)polymerase $\gamma$
B)polymerase $\delta$
C)polymerase $\varepsilon$
D)polymerase $\beta$
E)polymerase $\alpha$

Question 50

What is the name of the noncatalytic component of the DNA polymerase III holoenzyme that keeps the polymerase associated with the DNA template?

A) $\beta$ -pleated sheet
B) $\alpha$ -helix
C) $\beta$ clamp
D) $\alpha$ clamp
E) $\gamma$ clamp

Question 51

What is the average rate of replication in bacteria like E.coli?

A)about 100 nucleotides/sec
B)about 1,000 nucleotides/min
C)about 1,000 nucleotides/sec
D)about 10,000 nucleotides/sec
E)about 100 nucleotides/min

Question 52

Which eukaryotic DNA polymerase is thought to be the primary DNA-synthesizing enzyme during replication of the leading strand?

A)polymerase $\gamma$
B)polymerase $\delta$
C)polymerase $\varepsilon$
D)polymerase $\beta$
E)polymerase $\alpha$

Question 53

Why does it appear that each origin can only be activated once per cell cycle?

A)Mcm proteins are displaced from the DNA after replication and cannot reassociate with a replication origin that has already fired.
B)The ORC is denatured after replication and cannot return to the DNA.
C)The DNA becomes naked until the next round of cell division.
D)Mcm proteins reassociate with DNA immediately and prevent further replication from that DNA.
E)Mcm proteins bind to other proteins in the cytoplasm; together they actively inhibit further replication.

Question 54

The DNA polymerase can incorporate the wrong nucleotide occasionally.What is the probability that the wrong nucleotide is incorporated into the growing polynucleotide chain during replication?

A)fewer than 1 in 1 billion nucleotides
B)about 1 in 1000 nucleotides
C)fewer than 1 in about 4 million nucleotides
D)about 1 in 100,000 to 1,000,000 nucleotides
E)about 1 in 10,000 nucleotides

Question 55

Cyclin-dependent kinase activity stays high through mitosis after rising prior to DNA synthesis.Which of the following results from its elevated activity?

A)Chromosomes decondense.
B)It suppresses the formation of new prereplication complexes.
C)It enhances the formation of new prereplication complexes.
D)It enlarges the histones by removing their phosphate groups.
E)It shrinks the histones by binding amino groups to them.

Question 56

What binds to the ORC to assemble the prereplication complex (pre-RC)that is competent to initiate replication?

A)the ORC factors
B)licensing factors
C)competence factors
D)initiation factors
E)enlisting factors

Question 57

The clamp loader that loads PCNA onto DNA is called _______ and is analogous to the E.coli DNA polymerase III clamp loader complex.

A)RFC
B)KFC
C)NBC
D)TLC
E)SEC

Question 58

What is the probability that in E.coli an incorrect nucleotide will be incorporated into DNA during replication and remain there?

A)fewer than 1 in 1 billion nucleotides
B)about 1 in 1000 nucleotides
C)fewer than 1 in about 4 million nucleotides
D)about 1 in 100,000 to 1,000,000 nucleotides
E)about 1 in 10,000 nucleotides

Question 59

Which eukaryotic DNA polymerase is thought to be the primary DNA-synthesizing enzyme during replication of the lagging strand?

A)polymerase $\gamma$
B)polymerase $\delta$
C)polymerase $\varepsilon$
D)polymerase $\beta$
E)polymerase $\alpha$

Question 60

What evidence below suggested that the sequence of DNA was unimportant in the timing of replication?

A)The inactive,heterochromatized X chromosome in female mammals replicates late in S phase,while the active euchromatic X chromosome replicates at an earlier stage.
B)The inactive,heterochromatized X chromosome in female mammals replicates early in S phase,while the active euchromatic X chromosome replicates at a later stage.
C)The inactive,heterochromatized X chromosome in female mammals replicates late in M phase,while the active euchromatic X chromosome replicates at an earlier stage.
D)Incorporation of radioactive DNA precursors in replicating cells begins over heterochromatic regions in the nucleus.
E)Incorporation of radioactive DNA precursors in replicating cells ends over heterochromatic regions in the nucleus.

Question 61

In mammalian cells,a complex of proteins binds to the broken ends of the DNA duplex and catalyzes a series of reactions that rejoin the broken strands.This is an example of what kind of repair?

A)nucleotide excision repair
B)base excision repair
C)mismatch repair
D)double-strand breakage repair
E)nonhomologous end joining

Question 62

Which eukaryotic DNA polymerase appears to be the primary DNA-synthesizing enzyme during replication of the lagging strand?

A)polymerase $\gamma$
B)polymerase $\delta$
C)polymerase $\varepsilon$
D)polymerase $\beta$
E)polymerase $\alpha$

Question 63

Why did natural selection favor the use of thymine as a base in DNA instead of uracil even though uracil was presumably present in RNA,when it served as the genetic material during the early evolution of life?

A)Thymine was more stable.
B)Thymine paired better with adenine than did uracil.
C)Retention of uracil as a DNA base would make it hard to tell whether a uracil was supposed to be at a particular site or whether it resulted from damage to cytosine.
D)Thymine is resistant to all chemical treatments.
E)Retention of uracil as a DNA base would make it hard to tell whether a uracil was supposed to be at a particular site or whether it resulted from damage to guanine.

Question 64

What is the advantage of transcription-coupled repair?

A)It allows the cell to do two things at once.
B)It ensures that the genes of least importance to the cell receive the highest priority on the repair list.
C)It ensures that the genes of greatest importance to the cell receive the highest priority on the repair list.
D)It is repairs noncoding sequences preferentially.
E)It is the most accurate method of repair.

Question 65

What is responsible for removing the RNA primer and short DNA segment added by eukaryotic DNA polymerase $\alpha$ ?

A)FEN-1
B)DNA polymerase $\delta$
C)DNase H
D)both FEN-1 and DNase H
E)DNA ligase

Question 66

After cuts are made on the two sides of the lesion in nucleotide excision repair,what holds the damaged part of the strand in position for a while before its final removal?

A)ionic bonds
B)van der Waals forces
C)H bonds
D)3'-5' phosphodiester linkages
E)disulfide linkages

Question 67

What evidence suggests that the assembly of DNA into nucleosomes is a very rapid event?

A)Radiolabel is incorporated in a very short time.
B)Nucleosomes have a very unusual shape.
C)Electron micrographs of replicating DNA show nucleosomes forming on both daughter duplexes very near the replication fork.
D)Electron micrographs of replicating DNA show nucleosomes forming on both daughter duplexes at a large distance from the replication fork.
E)Nucleosomes are twice as big near the replication fork.

Question 68

Which type of DNA repair removes via a cut-and-patch mechanism a variety of bulky lesions,like pyrimidine dimers and nucleotides to which various chemical groups have been attached?

A)nucleotide excision repair
B)base excision repair
C)mismatch repair
D)double-strand breakage repair
E)All of these are correct.

Question 69

What enzyme is responsible for recognizing a chemical alteration in the DNA and removing the base by cleavage of the bond holding the base to the deoxyribose sugar moiety?

A)an AP endonuclease
B)phosphodiesterase activity of polymerase $\beta$
C)5'->3' exonuclease
D)3'->5' exonuclease
E)DNA glycosylase

Question 70

In the transcription-coupled repair pathway,how is the presence of a lesion thought to be detected?

A)There are special enzymes that scan the DNA for such lesions.
B)The lesion may be signaled by a stalled RNA polymerase.
C)The lesion may be signaled by a stalled DNA polymerase.
D)The lesion may be signaled by a stalled peptidyl transferase.
E)The lesion may be detected single-stranded binding proteins.

Question 71

What is responsible for joining eukaryotic Okazaki fragments together?

A)DNA ligase
B)DNA polymerase $\beta$
C)DNA polymerase $\delta$
D)DNA polymerase $\varepsilon$
E)RNase H1

Question 72

Which DNA repair mechanism recognizes a distortion in double helix geometry caused by DNA polymerase's insertion of an incorrect nucleotide during replication,one that escaped the enzyme's proofreading exonuclease?

A)nucleotide excision repair
B)base excision repair
C)mismatch repair
D)double-strand breakage repair
E)transcription-coupled pathway

Question 73

A double-stranded breakage repair pathway that requires the presence of a second chromosome carrying the same sequence of genes as the damaged chromosome is called _________.

A)nonhomologous end joining repair
B)homologous recombination
C)NHEJ
D)DNA methylation repair
E)nonhomologous recombination

Question 74

The stepwise assembly of nucleosomes and their orderly spacing along the DNA is facilitated by what?

A)a network of accessory proteins
B)a number of histone chaperones that are able to accept newly synthesized histones and transfer them to daughter strands
C)a number of histone chaperones that are able to accept parental histones and transfer them to daughter strands
D)CAF-1,which is able to accept either parental histones or newly synthesized histones and transfer them to daughter strands
E)All of these are correct.

Question 75

Which eukaryotic DNA polymerase appears to be the primary DNA-synthesizing enzyme during replication of the leading strand?

A)polymerase $\gamma$
B)polymerase $\delta$
C)polymerase $\varepsilon$
D)polymerase $\beta$
E)polymerase $\alpha$

Question 76

What enzyme cleaves the DNA backbone to remove the beheaded deoxyribose phosphate during base excision repair?

A)an AP endonuclease
B)phosphodiesterase activity of polymerase 
C)5'->3' exonuclease
D)3'->5' exonuclease
E)DNA glycosylase

Question 77

Which DNA repair mechanism removes altered nucleotides generated by reactive chemicals present in the diet or produced by metabolism?

A)nucleotide excision repair
B)base excision repair
C)mismatch repair
D)double-strand breakage repair
E)the global genomic pathway

Question 78

What is the most common mechanism for repairing damage to DNA?

A)direct repair of the damage
B)selective excision of the damaged section and use of the complementary strand to replace the excised portion
C)simple removal of damaged portion without replacement
D)simplistic repair of the damage
E)altruistic repair of the damage

Question 79

What is responsible for filling the gap left by the nucleases that digest the primer and the short DNA segment added to it by polymerase ?

A)DNA polymerase $\beta$
B)DNA polymerase $\delta$
C)DNA polymerase $\varepsilon$
D)both DNA polymerase $\beta$ and DNA polymerase $\delta$
E)RNase H1

Question 80

Patients with the classical form of xeroderma pigmentosum have a defect in one of the genes involved in ______________.

A)nucleotide excision repair
B)replication
C)base excision repair
D)transcription
E)base excitation repair