Question 1

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

Accepted Answer

Hershey and Chase's blender experiment using radioactive isotopes

Question 2

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

Accepted Answer

$$20\%$$

Question 3

Which of the following best describes the structure of a DNA double helix as determined by Watson and Crick?

Accepted Answer

Two antiparallel sugar-phosphate backbones with bases paired in the interior

Question 4

What is the significance of pairing a purine with a pyrimidine in the DNA double helix?

Accepted Answer

It results in a uniform width consistent with X-ray crystallography data

Question 5

Which enzyme is responsible for relieving the strain caused by unwinding of the DNA double helix during replication?

Accepted Answer

Topoisomerase

Question 6

During DNA replication, why is an RNA primer necessary?

Accepted Answer

DNA polymerase can only add nucleotides to an existing 3' end

Question 7

Which of the following statements about Okazaki fragments is correct?

Accepted Answer

They are joined together by DNA ligase on the lagging strand

Question 8

A mutation occurs during DNA replication. Which enzyme is most likely to correct this error immediately?

Accepted Answer

DNA polymerase

Question 9

What is the evolutionary significance of mutations that escape DNA repair mechanisms?

Accepted Answer

They are the source of genetic variation for natural selection

Question 10

Why do eukaryotic chromosomes have telomeres at their ends?

Accepted Answer

To prevent the loss of essential genes during DNA replication

Question 11

Which enzyme catalyzes the lengthening of telomeres in germ cells?

Accepted Answer

Telomerase

Question 12

In the Meselson-Stahl experiment, what result supported the semiconservative model of DNA replication?

Accepted Answer

After two generations, DNA molecules of intermediate and light densities were observed

Question 13

Which of the following best describes the role of histones in eukaryotic cells?

Accepted Answer

They package DNA into nucleosomes, aiding in chromatin structure

Question 14

A scientist exposes cells to X-rays, causing DNA damage. Which DNA repair mechanism is most likely to remove and replace the damaged DNA?

Accepted Answer

Nucleotide excision repair

Question 15

Which of the following statements about the directionality of DNA synthesis is correct?

Accepted Answer

DNA is synthesized in the 5' → 3' direction

Question 16

Which of the following is a direct consequence of the antiparallel structure of DNA?

Accepted Answer

One strand is synthesized continuously, the other discontinuously

Question 17

Which of the following best explains why DNA polymerase cannot initiate synthesis of a new strand?

Accepted Answer

It requires a free 3' hydroxyl group to add nucleotides

Question 18

Which of the following is NOT a function of the enzyme DNA ligase?

Accepted Answer

Synthesizing RNA primers

Question 19

A patient’s cells are found to have abnormally high telomerase activity. What is a possible consequence?

Accepted Answer

Increased risk of cancer due to unlimited cell division

Question 20

Which of the following best describes the organization of bacterial chromosomes?

Accepted Answer

Circular DNA molecules with a small amount of protein, found in the nucleoid

The Molecular Basis of Inheritance: DNA Structure and Replication

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