Question 1

Which experiment provided the first direct evidence that DNA, and not protein, is the genetic material responsible for inheritance in cells?

Accepted Answer

Hershey and Chase’s bacteriophage labeling experiment using $$^{32}P$$ and $$^{35}S$$

Question 2

In the Hershey and Chase experiment, why was $$^{32}P$$ used to label DNA and $$^{35}S$$ used to label protein?

Accepted Answer

$$^{32}P is $$incorporated into the phosphate backbone of DNA, while $$^{35}S is $$found in the sulfur-containing amino acids of proteins.

Question 3

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

Accepted Answer

One strand runs 5′ to 3′, and the other runs 3′ to 5′.

Question 4

A scientist isolates a DNA sample and finds that 30% of the bases are adenine. According to Chargaff’s rules, what percentage of the bases should be cytosine?

Accepted Answer

20%

Question 5

During DNA replication, which enzyme is responsible for relieving the twisting stress ahead of the replication fork?

Accepted Answer

Topoisomerase

Question 6

Why is an RNA primer necessary for DNA polymerase to begin synthesis of a new DNA strand?

Accepted Answer

DNA polymerase can only add nucleotides to an existing 3′-OH group.

Question 7

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are short DNA fragments synthesized on the lagging strand.

Question 8

What is the function of DNA ligase during DNA replication?

Accepted Answer

It joins Okazaki fragments together by forming phosphodiester bonds.

Question 9

A mutation in the gene encoding DNA polymerase eliminates its 3′ to 5′ exonuclease activity. What is the most likely consequence?

Accepted Answer

The accuracy of DNA replication will decrease due to loss of proofreading.

Question 10

Why do linear chromosomes in eukaryotes require telomeres and the enzyme telomerase?

Accepted Answer

To prevent the loss of essential genetic information at the ends of chromosomes during DNA replication.

Question 11

Which of the following best explains the semi-conservative model of DNA replication?

Accepted Answer

Each new DNA molecule consists of one parental strand and one newly synthesized strand.

Question 12

A cell is exposed to UV light, causing thymine dimers to form in its DNA. Which repair mechanism is most likely to fix this damage?

Accepted Answer

Nucleotide excision repair

Question 13

Which feature of DNA allows it to interact with histone proteins in chromosomes?

Accepted Answer

Its negatively charged phosphate backbone

Question 14

In prokaryotic DNA replication, what is the significance of having a single origin of replication?

Accepted Answer

Replication proceeds bidirectionally from the origin, allowing rapid copying of the circular chromosome.

Question 15

Which of the following best describes the role of single-strand binding proteins during DNA replication?

Accepted Answer

They keep the separated DNA strands from re-annealing.

Question 16

A DNA molecule is found to have 18% guanine. What is the percentage of thymine in this molecule?

Accepted Answer

32%

Question 17

Which of the following is a direct result of the antiparallel structure of DNA during replication?

Accepted Answer

One strand is synthesized continuously, and the other is synthesized in fragments.

Question 18

Which of the following equations correctly represents the base pairing in double-stranded DNA according to Chargaff’s rules?

Accepted Answer

$$[A] = [T]$$ and $$[G] = [C]$$

Question 19

During DNA synthesis, which chemical reaction provides the energy for the addition of a nucleotide to the growing DNA strand?

Accepted Answer

Release and subsequent hydrolysis of pyrophosphate ($$PP_i) $$from the incoming nucleotide triphosphate

The Molecular Basis of Inheritance: DNA Structure and Replication

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