Question 1

Which of the following equations is NOT consistent with Erwin Chargaff’s findings regarding double-stranded DNA?

Accepted Answer

$$(C + G) = (A + T)$$

Question 2

The molecule shown in the image contains a ribose sugar and a double-ringed nitrogenous base. Which of the following best describes this molecule?

Accepted Answer

RNA; purine

Question 3

Which experiment provided strong evidence that DNA replication is semiconservative in prokaryotes?

Accepted Answer

Meselson–Stahl experiment using 15N labeling

Question 4

In the Meselson–Stahl experiment, what would be observed after one generation of E. coli grown in 14N medium following initial growth in 15N medium, assuming semiconservative replication?

Accepted Answer

All DNA would be 15N/14N

Question 5

Which of the following statements about DNA replication in bacteria is correct?

Accepted Answer

Replication begins at a single origin and proceeds bidirectionally

Question 6

What is the main purpose of using equilibrium density gradient centrifugation in the Meselson–Stahl experiment?

Accepted Answer

To separate DNA based on its weight/density

Question 7

Which of the following best describes semiconservative replication?

Accepted Answer

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

Question 8

In the Taylor–Woods–Hughes experiment, what was the significance of using 3H-thymidine and autoradiography?

Accepted Answer

It allowed visualization of newly synthesized DNA

Question 9

If DNA replication were conservative instead of semiconservative, what would be the expected result after one generation in the Meselson–Stahl experiment?

Accepted Answer

Half DNA would be 15N/15N and half 14N/14N

Question 10

Which of the following is a critical feature of the origin of replication (ORI) in bacterial DNA?

Accepted Answer

It is the site where the DNA helix is unwound and replication begins

Question 11

A student claims that after three generations in 14N medium, all DNA in the Meselson–Stahl experiment will be 14N/14N. Is this correct? Why or why not?

Accepted Answer

No, because some DNA will still have 15N/14N strands

Question 12

Which of the following best explains why the percentages of A and T, and C and G, are equal in double-stranded DNA?

Accepted Answer

A pairs with T and C pairs with G due to strand complementarity

Question 13

Which of the following is NOT a plausible outcome of the Meselson–Stahl experiment if DNA replication were dispersive?

Accepted Answer

DNA would separate into distinct heavy and light bands

Question 14

Which of the following statements about the replicon in bacterial DNA is correct?

Accepted Answer

It refers to the length of DNA replicated from a single origin

Question 15

A scientist observes that only one chromatid is labeled after DNA replication in a eukaryotic cell using 3H-thymidine. What does this indicate?

Accepted Answer

DNA replication is semiconservative

Question 16

Which of the following is a real-world application of understanding semiconservative DNA replication?

Accepted Answer

Designing antibiotics that target DNA polymerase in bacteria

Question 17

If a mutation occurs at the origin of replication (ORI) in a bacterial chromosome, which of the following is the most likely consequence?

Accepted Answer

Replication may fail to initiate, preventing cell division

Question 18

Which of the following best describes the role of autoradiography in the Taylor–Woods–Hughes experiment?

Accepted Answer

It pinpoints the location of newly synthesized DNA by detecting radioisotope grains

Question 19

Which of the following statements about the Meselson–Stahl experiment is correct?

Accepted Answer

It demonstrated that DNA replication is semiconservative by showing intermediate density bands

DNA Replication: Semiconservative Mechanism and Experimental Evidence

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