Question 1

If DNA repair mechanisms fail,what is the result?

Accepted Answer

Failure of DNA repair mechanisms can lead to a wide range of consequences, including mutations, defective enzymes, and cancer. Therefore, all of the above options can result from the failure of DNA repair mechanisms.

Question 2

In the mismatch repair process,enzyme complexes replace bases that were incorrectly inserted into the newly synthesized DNA strand.To function,they must be able to distinguish between the parent DNA strand and the new strand.How is this accomplished?

Accepted Answer

The parent strand is methylated, meaning it has added methyl groups to certain nucleotides. These methyl groups are absent from the newly synthesized DNA strand, allowing the mismatch repair enzyme complexes to distinguish between the two strands.

Question 3

What are pyrimidine dimers?

Accepted Answer

Pyrimidine dimers refer to adjacent pyrimidines (usually thymine) on the same DNA strand that join by covalent bonding, forming a structure that disrupts DNA replication and transcription. The most common type of pyrimidine dimer is the cyclobutane pyrimidine dimer (CPD), which forms when two adjacent thymines on the same strand of DNA are photochemically linked by a covalent bond. Pyrimidine dimers are considered a type of DNA damage and can be caused by exposure to UV radiation or certain chemical agents.

Question 4

In humans,xeroderma pigmentosum is a disorder of the nucleotide excision repair mechanism.These individuals are unable to repair DNA damage caused by ultraviolet light.Which of the following are the most prominent types of mutations in individuals suffering from xeroderma pigmentosum?

Accepted Answer

Pyrimidine dimers are the most prominent type of DNA damage caused by ultraviolet light, and individuals suffering from xeroderma pigmentosum are unable to repair this type of damage.

Question 5

-Where would Okazaki fragments be found in the image above? Note: The black boxes represent RNA primers and the polarities of the template strands are indicated.
A)A,B
B)C,D
C)A,C
D)B,D
E)A,D

Accepted Answer

The answer of 
-Where would Okazaki fragments be found in...

Question 6

In a healthy cell,the rate of DNA repair is equal to the rate of DNA mutation.When the rate of repair lags behind the rate of mutation,what is a possible fate of the cell?

Accepted Answer

When the rate of DNA repair lags behind the rate of mutation, it can lead to the accumulation of mutations in the DNA, which can result in the cell becoming cancerous. Cancer cells have a high rate of DNA mutations and a low rate of DNA repair.

Question 7

Which of the following agents can cause mutations in DNA?

Accepted Answer

All of the listed agents can cause mutations in DNA. Aflatoxins can cause DNA damage and mutations by binding to DNA and disrupting its structure. Free radicals can react with and damage DNA, leading to mutations. Ultraviolet radiation can cause thymine dimers, which disrupt DNA replication and can lead to mutations.

Question 8

Researchers found E.coli that had mutation rates 100 times higher than normal.What is a possible explanation for these results?

Accepted Answer

The proofreading mechanism of DNA polymerase plays a critical role in correcting errors during DNA replication. When this mechanism is not working properly, there is an increased chance of mutations occurring at a higher rate than normal. Therefore, option C is the best choice as a possible explanation for the results obtained.

Question 9

DNA replication is highly accurate.It results in about one mistake per billion nucleotides.For the human genome,how often would errors occur?

Accepted Answer

The answer of DNA replication is highly accurate.It results in...

Question 10

If during the process of DNA replication,the enzyme topoisomerase was not functioning (i.e.it was mutated)what do you expect will happen to the replication process?

Accepted Answer

Topoisomerase relieves the tension that builds up ahead of the replication fork by making transient breaks in the DNA. Mutations in Topoisomerase would result in over-twisting of the DNA, causing premature termination of replication. Therefore, B is the correct choice. Choices A, C, and D are not likely outcomes of a Topoisomerase mutation.

Question 11

The epsilon (ε)subunit of DNA polymerase III of E.coli has exonuclease activity.How does it function in the proofreading process?

Accepted Answer

The epsilon subunit of DNA polymerase III of E.coli functions in the proofreading process by removing a mismatched nucleotide. This is accomplished through its exonuclease activity, which allows it to backtrack along the newly synthesized DNA strand and remove the incorrect base. Once the mismatched nucleotide has been removed, the polymerase activity of the enzyme can resume and the correct nucleotide can be added to the growing DNA strand.

Question 12

What is a telomere?

Accepted Answer

Telomeres are the ends of linear chromosomes that consist of repetitive DNA sequences that protect the genetic material during cell division and prevent the loss of important genetic information.

Question 13

Which of the following cells do not have active telomerase activity?

Accepted Answer

Most normal somatic cells do not have active telomerase activity. Telomerase activity is more commonly found in cells with high proliferative potential such as germ cells and cancer cells.

Question 14

Hereditary nonpolyposis colorectal cancer (HNPCC)is an inherited disorder.The genetic defect identified is an error in the mismatch repair mechanism.Which of the following would be an expected result of this mutation?

Accepted Answer

HNPCC is caused by a mutation in the mismatch repair mechanism, which leads to a decreased ability to repair certain DNA mutations. This increases the risk of developing colorectal cancer and other cancers.

Question 15

Bodnar et al.(1998)used telomerase to extend the life span of normal human cells.Telomere shortening puts a limit on the number of times a cell can divide.How might adding telomerase affect cellular aging?

Accepted Answer

Adding telomerase would ensure that the ends of chromosomes (telomeres) are accurately replicated, eliminating the shortening that occurs with each cell division. This would prevent the cell from reaching its replicative limit and extend its ability to divide, ultimately delaying cellular aging. However, it is worth noting that telomerase activation can also have negative consequences, such as promoting uncontrolled cell growth (cancer).

Question 16

Recent studies have shown that xeroderma pigmentosum (an error in the nucleotide excision repair process)can result from mutations in one of seven genes.What can you infer from this finding?

Accepted Answer

The fact that mutations in seven different genes can result in the same error (xeroderma pigmentosum) suggests that there are multiple enzymes involved in the nucleotide excision repair process.

Question 17

Which of the following would be least likely to cause DNA damage in an individual suffering from xeroderma pigmentosum?

Accepted Answer

Incandescent light bulbs do not emit harmful UV radiation, so they would be the least likely to cause DNA damage in an individual with xeroderma pigmentosum. Natural lighting, low-level ultraviolet lights, and reflected sunlight are all sources of harmful UV radiation that could cause DNA damage in someone with this condition.

Question 18

Telomere shortening is a problem in which types of cells?

Accepted Answer

Telomere shortening is a problem in eukaryotic cells. Prokaryotes do not have telomeres because their DNA is circular and does not have linear ends like those found in eukaryotic chromosomes.

Question 19

Which of the following are important in reducing the errors in DNA replication in E.coli organisms?

Accepted Answer

All of the choices listed (proofreading activity of DNA polymerase III, mismatch repair, and nucleotide excision repair) are important mechanisms in minimizing errors in DNA replication in E.coli organisms. The proofreading activity of DNA polymerase III checks for incorrect nucleotides that are incorporated during replication and replaces them with correct nucleotides. Mismatch repair corrects errors that may arise from base mis-pairings after DNA replication. Nucleotide excision repair corrects errors resulting from DNA damage caused by mutagens or other environmental factors. Together, these mechanisms work to minimize errors in DNA replication in E.coli.

Quiz 14: Dna and the Gene: Synthesis and Repair

If DNA repair mechanisms fail,what is the result?

In the mismatch repair process,enzyme complexes replace bases that were incorrectly inserted into the newly synthesized DNA strand.To function,they must be able to distinguish between the parent DNA strand and the new strand.How is this accomplished?

What are pyrimidine dimers?

In humans,xeroderma pigmentosum is a disorder of the nucleotide excision repair mechanism.These individuals are unable to repair DNA damage caused by ultraviolet light.Which of the following are the most prominent types of mutations in individuals suffering from xeroderma pigmentosum?

-Where would Okazaki fragments be found in the image above? Note: The black boxes represent RNA primers and the polarities of the template strands are indicated. A)A,B B)C,D C)A,C D)B,D E)A,D

In a healthy cell,the rate of DNA repair is equal to the rate of DNA mutation.When the rate of repair lags behind the rate of mutation,what is a possible fate of the cell?

Which of the following agents can cause mutations in DNA?

Researchers found E.coli that had mutation rates 100 times higher than normal.What is a possible explanation for these results?

DNA replication is highly accurate.It results in about one mistake per billion nucleotides.For the human genome,how often would errors occur?

If during the process of DNA replication,the enzyme topoisomerase was not functioning (i.e.it was mutated) what do you expect will happen to the replication process?

The epsilon (ε) subunit of DNA polymerase III of E.coli has exonuclease activity.How does it function in the proofreading process?

What is a telomere?

Which of the following cells do not have active telomerase activity?

Hereditary nonpolyposis colorectal cancer (HNPCC) is an inherited disorder.The genetic defect identified is an error in the mismatch repair mechanism.Which of the following would be an expected result of this mutation?

Bodnar et al.(1998) used telomerase to extend the life span of normal human cells.Telomere shortening puts a limit on the number of times a cell can divide.How might adding telomerase affect cellular aging?

Recent studies have shown that xeroderma pigmentosum (an error in the nucleotide excision repair process) can result from mutations in one of seven genes.What can you infer from this finding?

Which of the following would be least likely to cause DNA damage in an individual suffering from xeroderma pigmentosum?

Telomere shortening is a problem in which types of cells?

Which of the following are important in reducing the errors in DNA replication in E.coli organisms?