Question 1

Which experiment provided the first direct evidence that DNA, and not protein, is the genetic material in viruses?

Accepted Answer

Hershey and Chase's experiment using radioactive labeling of T2 phage DNA and protein

Question 2

A scientist is studying a newly discovered organism and finds that its DNA contains 30% adenine. According to Chargaff's rules, what percentage of guanine would you expect to find?

Accepted Answer

$$20\%$$

Question 3

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

Accepted Answer

The two DNA strands have complementary base sequences and run in opposite directions: one 5' to 3', the other 3' to 5'.

Question 4

During DNA replication, which enzyme is responsible for relieving the strain caused by unwinding of the double helix ahead of the replication fork?

Accepted Answer

Topoisomerase

Question 5

A mutation disables DNA polymerase I in a bacterial cell. Which of the following would most likely occur during DNA replication?

Accepted Answer

RNA primers would not be replaced with DNA on the lagging strand.

Question 6

Which of the following statements about eukaryotic and bacterial chromosomes is correct?

Accepted Answer

Bacterial chromosomes are circular and found in the nucleoid, while eukaryotic chromosomes are linear and found in the nucleus.

Question 7

Why is DNA replication described as semiconservative?

Accepted Answer

Each new DNA molecule consists of one old (parental) strand and one new strand.

Question 8

Which of the following best explains why DNA synthesis occurs in opposite directions on the two template strands at a replication fork?

Accepted Answer

DNA polymerase can only add nucleotides to the 3' end, so one strand is synthesized continuously toward the fork (leading), and the other discontinuously away from the fork (lagging).

Question 9

A cell is observed to have highly condensed chromatin and very low levels of gene expression. Which chromatin state is most likely present, and what is the implication for gene accessibility?

Accepted Answer

Heterochromatin; genes are largely inaccessible

Question 10

Which of the following is a direct function of telomeres in eukaryotic chromosomes?

Accepted Answer

They prevent the loss of coding DNA during replication by acting as a buffer zone.

Question 11

A researcher is studying a cancer cell line and finds that the cells can divide indefinitely without losing essential genetic information. Which enzyme is most likely abnormally active in these cells, and what is its function?

Accepted Answer

Telomerase; extends telomeres to prevent chromosome shortening

Question 12

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

Accepted Answer

It synthesizes short RNA primers to provide a starting point for DNA polymerase.

Question 13

During the S phase of the cell cycle, what is the main purpose of DNA replication?

Accepted Answer

To ensure that each daughter cell receives a complete set of genetic information during mitosis

Question 14

Which of the following is NOT a function of single-strand binding proteins during DNA replication?

Accepted Answer

Catalyzing the joining of Okazaki fragments

Question 15

A mutation causes a eukaryotic cell to lack histone proteins. Which of the following would most likely result?

Accepted Answer

DNA would not be packaged efficiently, leading to problems fitting into the nucleus

Question 16

Which of the following best illustrates an epigenetic change?

Accepted Answer

Methylation of DNA bases leading to reduced gene expression without changing the DNA sequence

Question 17

Which enzyme is responsible for joining the sugar-phosphate backbones of Okazaki fragments during DNA replication?

Accepted Answer

DNA ligase

Question 18

A patient is diagnosed with a rare genetic disorder that causes rapid telomere shortening in somatic cells. Which of the following is a likely consequence?

Accepted Answer

Premature aging and early loss of tissue regenerative capacity

Question 19

Which of the following best explains why Okazaki fragments are formed during DNA replication?

Accepted Answer

DNA polymerase can only synthesize DNA in the 5' to 3' direction, so the lagging strand is synthesized discontinuously away from the replication fork.

Question 20

Which of the following is a direct result of the double-helix structure of DNA as proposed by Watson and Crick?

Accepted Answer

Specific base pairing allows for accurate copying of genetic information during replication.

DNA Structure, Replication, and Chromosome Organization

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