Question 1

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?

Accepted Answer

Nonhomologous end joining is a pathway that repairs double-strand breaks in DNA by directly ligating the broken ends without the need for a homologous template.

Question 2

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

Accepted Answer

Polymerase F1F1F1S1F1F1F10 appears to be the primary DNA-synthesizing enzyme during replication of the lagging strand. This is because it has a high processivity and proofreading ability, which helps ensure accurate synthesis and repair of DNA on the lagging strand.

Question 3

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?

Accepted Answer

The answer of Why did natural selection favor the use...

Question 4

What is the advantage of transcription-coupled repair?

Accepted Answer

Transcription-coupled repair prioritizes the repair of genes that are actively being transcribed, which are likely to be of greater importance to the cell. This helps ensure the survival of the cell and the integrity of its genetic information.

Question 5

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

Accepted Answer

FEN-1 (Flap Endonuclease 1) is responsible for removing the RNA primer and the short DNA segment during DNA replication in eukaryotes.

Question 6

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?

Accepted Answer

Hydrogen bonds hold the damaged part of the strand in position for a while before its final removal during nucleotide excision repair.

Question 7

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

Accepted Answer

Electron micrographs of replicating DNA show nucleosomes forming on both daughter duplexes very near the replication fork, indicating that nucleosomes assemble quickly on newly replicated DNA.

Question 8

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?

Accepted Answer

Nucleotide excision repair is the type of DNA repair that removes bulky lesions, such as pyrimidine dimers, via a cut-and-patch mechanism. This repair process involves the removal of a short segment of damaged DNA and the subsequent replacement with a newly synthesized strand. Base excision repair, mismatch repair, and double-strand breakage repair are different types of DNA repair mechanisms that do not involve the removal of bulky lesions.

Question 9

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?

Accepted Answer

DNA glycosylase is the enzyme responsible for recognizing a chemical alteration in the DNA, such as damaged or incorrect bases, and removes the base by cleaving the bond holding the base to the deoxyribose sugar moiety. This process is known as base excision repair.

Question 10

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

Accepted Answer

In the transcription-coupled repair pathway, the presence of a lesion is thought to be detected when RNA polymerase stalls at the lesion site, signaling the need for repair. This mechanism ensures that lesions that may interfere with transcription are repaired in a timely manner.

Question 11

What is responsible for joining eukaryotic Okazaki fragments together?

Accepted Answer

The enzyme responsible for joining eukaryotic Okazaki fragments together is DNA ligase. It creates a phosphodiester bond between the 3' hydroxyl group of one nucleotide and the 5' phosphate group of another nucleotide, ultimately sealing the nicks between adjacent Okazaki fragments. DNA polymerases are responsible for the synthesis of the fragments themselves, but cannot join them together. RNase H1 is a ribonuclease that cleaves RNA in RNA-DNA hybrid molecules, and is not involved in the joining of Okazaki fragments. Among the three DNA polymerases listed, only polymerase δ and ε are involved in DNA replication in eukaryotic cells while polymerase β is mainly involved in DNA repair, but none of them can join Okazaki fragments together.

Question 12

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?

Accepted Answer

Mismatch repair is the DNA repair mechanism that 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. Mismatch repair corrects base mismatches, insertions, or deletions in the newly synthesized DNA strand. Nucleotide excision repair corrects bulky DNA base adducts, while base excision repair corrects oxidative damage to DNA bases. Double-strand breakage repair repairs double-strand breaks, while transcription-coupled pathway repairs DNA damage that interferes with transcription.

Question 13

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 _________.

Accepted Answer

Homologous recombination is a double-stranded breakage repair pathway that requires the presence of a second chromosome carrying the same sequence of genes as the damaged chromosome. Nonhomologous end joining repair (NHEJ) is another type of double-stranded breakage repair, but it does not require a second chromosome carrying the same sequence of genes. DNA methylation repair and nonhomologous recombination are not accurate descriptions of any known repair pathways.

Question 14

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

Accepted Answer

The stepwise assembly of nucleosomes and their orderly spacing along the DNA is facilitated by a network of accessory proteins, as well as a number of histone chaperones that are able to accept either parental histones or newly synthesized histones and transfer them to daughter strands. CAF-1 is one such histone chaperone that is involved in this process. Therefore, all of the choices given are correct.

Question 15

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

Accepted Answer

DNA polymerase ε is primarily responsible for synthesizing the leading strand during eukaryotic DNA replication.

Question 16

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

Accepted Answer

AP endonuclease cleaves the DNA backbone to remove the beheaded deoxyribose phosphate during base excision repair.

Question 17

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

Accepted Answer

Base excision repair removes altered nucleotides, such as those generated by reactive chemicals or produced by metabolism. Nucleotide excision repair removes bulky lesions, mismatch repair corrects errors during DNA replication, double-strand breakage repair fixes double-strand breaks, and the global genomic pathway repairs multiple types of lesions simultaneously.

Question 18

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

Accepted Answer

Selective excision repair, also known as nucleotide excision repair, is the most common mechanism for repairing damage to DNA. It involves the removal of the damaged section of DNA and use of the complementary strand to replace the excised portion. This mechanism can repair a variety of different types of DNA damage, including UV-induced damage and chemically-induced damage.

Question 19

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 ?

Accepted Answer

DNA polymerase δ is responsible for filling the gap left by the nucleases that digest the RNA primer and the short DNA segment added to it by polymerase α during DNA replication.

Question 20

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

Accepted Answer

Patients with classical xeroderma pigmentosum have a defect in nucleotide excision repair, which is responsible for repairing DNA damage caused by UV radiation. This defect leads to an increased susceptibility to skin cancer and other types of cancer due to the accumulation of DNA damage in skin cells. Replication, base excision repair, and base excitation repair are not directly implicated in the pathology of xeroderma pigmentosum. Transcription is also not directly implicated, but it may be affected secondarily due to the accumulation of DNA damage.

Quiz 13: Dna Replication and Repair

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?

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

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?

What is the advantage of transcription-coupled repair?

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

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?

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

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?

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?

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

What is responsible for joining eukaryotic Okazaki fragments together?

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 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 _________.

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

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

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

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

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

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 ?

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

Quiz 13: Dna Replication and Repair

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?

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

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?

What is the advantage of transcription-coupled repair?

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

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?

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

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?

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?

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

What is responsible for joining eukaryotic Okazaki fragments together?

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 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 _________.

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

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

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

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

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

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 ?

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

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