Question 1

Which experiment provided the strongest evidence that DNA, and not protein, is the genetic material in phages?

Accepted Answer

The Hershey-Chase experiment using radioactive labeling of DNA and protein

Question 2

What is the chemical bond that links nucleotides together in the backbone of a DNA strand?

Accepted Answer

Phosphodiester bond

Question 3

According to Chargaff's rules, if a DNA sample contains 30% adenine, what percentage of guanine would you expect?

Accepted Answer

$$20\%$$

Question 4

Which of the following best describes the antiparallel nature of DNA?

Accepted Answer

One strand runs $$5' \rightarrow 3'$$, the other runs $$3' \rightarrow 5'$$

Question 5

A scientist isolates a DNA molecule and finds that it is composed of 24% thymine. What is the expected percentage of cytosine?

Accepted Answer

$$26\%$$

Question 6

Which enzyme is responsible for unwinding the DNA double helix during replication?

Accepted Answer

Helicase

Question 7

During DNA replication, why is an RNA primer necessary?

Accepted Answer

DNA polymerase can only add nucleotides to an existing $$3'$$ hydroxyl group

Question 8

Which enzyme removes RNA primers and replaces them with DNA nucleotides during lagging strand synthesis in E. coli?

Accepted Answer

DNA polymerase I

Question 9

What is the main function of DNA ligase during DNA replication?

Accepted Answer

Joining Okazaki fragments by forming phosphodiester bonds

Question 10

The Meselson-Stahl experiment demonstrated that DNA replication is semiconservative. What does this mean?

Accepted Answer

Each daughter DNA molecule consists of one old and one new strand

Question 11

A DNA template strand has the sequence $$3'-AAGTCAGT-5'. $$What is the sequence of the newly synthesized complementary strand?

Accepted Answer

$$5'-TTCAGTCA-3'$$

Question 12

Why do eukaryotic chromosomes have telomeres?

Accepted Answer

To postpone the erosion of genes near the ends of DNA molecules

Question 13

Which enzyme is responsible for extending telomeres in eukaryotic cells?

Accepted Answer

Telomerase

Question 14

A patient with Xeroderma Pigmentosum (XP) is highly sensitive to sunlight due to a defect in which DNA repair pathway?

Accepted Answer

Nucleotide excision repair

Question 15

Which of the following best explains why DNA polymerase has a low error rate during DNA replication?

Accepted Answer

It has $$3' \rightarrow 5'$$ exonuclease activity for proofreading

Question 16

A chemical in cigarette smoke causes bulky DNA adducts that distort the double helix. Which repair mechanism is most likely to fix this damage?

Accepted Answer

Nucleotide excision repair

Question 17

If a mutation in the gene encoding DNA ligase occurred, which process would be most directly affected?

Accepted Answer

Joining of Okazaki fragments on the lagging strand

Question 18

Which of the following statements about the leading and lagging strands during DNA replication is correct?

Accepted Answer

The lagging strand is synthesized discontinuously in short fragments

Question 19

Which of the following best describes the role of topoisomerase during DNA replication?

Accepted Answer

It relieves overwinding strain ahead of the replication fork

Question 20

A mutation in the gene encoding a mismatch repair protein increases the risk of which type of disease?

Accepted Answer

Hereditary non-polyposis colon cancer (HNPCC)

DNA and the Gene: Synthesis and Repair – Study Notes

Study Guide - Practice Questions