Question 1

Which of the following best describes the mechanism of DNA replication in E. coli?

Accepted Answer

Semi-conservative and bidirectional

Question 2

During lagging strand synthesis in E. coli, which enzyme is responsible for removing RNA primers and replacing them with DNA?

Accepted Answer

DNA polymerase I

Question 3

Which of the following is a key difference between DNA replication in E. coli and in human cells?

Accepted Answer

Human cells have multiple origins of replication per chromosome, while E. coli has only one

Question 4

Which enzyme introduces negative supercoils into DNA to relieve torsional strain ahead of the replication fork in E. coli?

Accepted Answer

DNA gyrase

Question 5

A patient with extreme sensitivity to sunlight and a high risk of skin cancer is most likely to have a defect in which DNA repair pathway?

Accepted Answer

Nucleotide excision repair

Question 6

Which of the following best describes the function of telomerase in eukaryotic cells?

Accepted Answer

It extends the 3' end of linear chromosomes using an RNA template

Question 7

Which of the following agents acts directly on DNA polymerases to inhibit DNA replication in viruses?

Accepted Answer

Acyclovir

Question 8

A mutation that changes a cytosine to a thymine is classified as which type of base substitution?

Accepted Answer

Transition

Question 9

The Ames test is used to assess the mutagenic potential of chemicals. Which of the following outcomes indicates a positive result in the Ames test?

Accepted Answer

The test strain of Salmonella survives and grows on histidine-deficient medium

Question 10

Which of the following best explains why Okazaki fragments are shorter in eukaryotes than in prokaryotes?

Accepted Answer

Eukaryotic Okazaki fragments are limited by nucleosome spacing

Question 11

Which of the following DNA repair mechanisms is most likely to be error-prone and activated in response to extensive UV-induced DNA damage?

Accepted Answer

SOS repair

Question 12

A patient is diagnosed with hereditary nonpolyposis colon cancer (HNPCC). Which DNA repair pathway is most likely defective?

Accepted Answer

Mismatch repair

Question 13

Which of the following best describes the role of photolyase in DNA repair?

Accepted Answer

It uses visible light to cleave pyrimidine dimers

Question 14

Which of the following is a consequence of a defect in the ATM gene, as seen in ataxia telangiectasia?

Accepted Answer

Increased sensitivity to ionizing radiation

Question 15

Which of the following best explains why DNA ligase cannot seal a gap in the DNA backbone?

Accepted Answer

DNA ligase requires a 5' phosphate and a 3' hydroxyl group on adjacent nucleotides

Question 16

Which of the following diseases is associated with defective repair of interstrand cross-links or x-ray induced DNA damage?

Accepted Answer

Fanconi's anemia

Question 17

A chemical agent causes the formation of O6-methylguanine in DNA. Which enzyme is responsible for direct reversal of this damage?

Accepted Answer

O6-methylguanine-DNA methyltransferase (MGMT)

Question 18

Which of the following best describes the function of the ε subunit of E. coli DNA polymerase III?

Accepted Answer

It provides 3' to 5' exonuclease proofreading activity

Question 19

Which of the following is a real-life application of rolling-circle replication?

Accepted Answer

Replication of phage DNA and bacterial conjugation

Question 20

A patient presents with premature aging, cataracts, and growth retardation. Which DNA repair disorder is most likely?

Accepted Answer

Cockayne's syndrome

DNA Replication, Repair, and Mutagenesis: Biochemistry Study Notes

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