Question 1

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

Accepted Answer

Xeroderma pigmentosum is a genetic disorder that affects the nucleotide excision repair pathway, which is responsible for repairing damaged DNA caused by UV radiation. Defects in this pathway can lead to an increased risk of skin cancer and other types of cancer.

Question 2

You are the enzyme responsible for carrying out mismatch repair.You notice a mismatched pair in the DNA strand and you know it is your job to remove one of the bases in the mismatched pair.How would you decide which nucleotide to remove?

Accepted Answer

The answer of You are the enzyme responsible for carrying...

Question 3

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 requires the presence of a second chromosome with the same sequence of genes in order to repair a double-stranded breakage. Nonhomologous end joining repair (NHEJ) on the other hand, does not require homologous sequence and can result in loss or gain of genetic information. DNA methylation repair and nonhomologous recombination are not recognized repair pathways.

Question 4

What enzyme activity are the Mcm proteins (Mcm2 - Mcm7)thought to exhibit once they have been loaded onto the replication origin and associated into a ring-shaped complex? What role does this enzyme activity play in replication and to what protein in E.coli is it analogous?

Accepted Answer

The answer of What enzyme activity are the Mcm proteins...

Question 5

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 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.

Question 6

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. This mechanism identifies the incorrect nucleotide, removes it, and replaces it with the correct one using the complementary strand as a template. This repair process is crucial for maintaining the integrity of the genetic information during DNA replication.

Question 7

You are studying replication in a particular bacterial strain.At 37°C,the bacteria appear perfectly normal.If the temperature is raised to 43°C,however,they stop growing and are unable to replicate their DNA.If some of them are placed back at 37°C,they begin to replicate their DNA and are again perfectly normal.What is wrong?

Accepted Answer

The answer of You are studying replication in a particular...

Question 8

What happens once damage caused by lesions in the genome,like a thymidine dimer,is bypassed during replication and replication must continue?

Accepted Answer

Once the damage is bypassed, the normal replicative DNA polymerase resumes replication to ensure high fidelity and processivity.

Question 9

After exonucleases have excised the damaged portion of DNA,how can DNA polymerase fill in the gap? Is there a primer?

Accepted Answer

The answer of After exonucleases have excised the damaged portion...

Question 10

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 11

The DNA polymerases in a relatively large family of polymerases in which each member is specialized for incorporating nucleotides opposite particular types of DNA lesions in the template strand engage in a type of DNA synthesis called __________.They have an unusually spacious active site that ____________.

Accepted Answer

The statement describes the process of translesion synthesis which involves specialized DNA polymerases that can incorporate nucleotides opposite specific DNA lesions in the template strand. These polymerases have an unusually spacious active site which allows them to physically accommodate altered nucleotides that would not fit in the active site of a replicative polymerase.

Question 12

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

The answer of In mammalian cells,a complex of proteins binds...

Quiz 13: Dna Replication and Repair