Question 1

Which of the following statements best explains Chargaff’s rules regarding DNA base composition?

Accepted Answer

The amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C) in any species.

Question 2

Rosalind Franklin’s X-ray diffraction photograph of DNA was critical evidence for which feature of DNA structure?

Accepted Answer

The double helical structure with a uniform width.

Question 3

Which enzyme is responsible for relieving the overwinding strain ahead of the replication fork during DNA replication?

Accepted Answer

Topoisomerase

Question 4

During DNA replication, why is the lagging strand synthesized discontinuously?

Accepted Answer

The lagging strand template runs in the 3' to 5' direction, requiring synthesis away from the replication fork in short segments.

Question 5

Which of the following best describes the role of DNA ligase in DNA replication?

Accepted Answer

It joins Okazaki fragments together by forming phosphodiester bonds.

Question 6

A mutation causes a cell to lack functional single-strand binding proteins. What is the most likely consequence during DNA replication?

Accepted Answer

The separated DNA strands will re-anneal or form secondary structures, impeding replication.

Question 7

Which of the following equations correctly represents the directionality of DNA synthesis?

Accepted Answer

$$5' \rightarrow 3'$$

Question 8

Why do eukaryotic chromosomes have multiple origins of replication?

Accepted Answer

Because eukaryotic chromosomes are much larger and require multiple starting points to replicate efficiently.

Question 9

What is the function of telomeres in eukaryotic chromosomes?

Accepted Answer

They postpone the erosion of genes near the ends of DNA molecules during replication.

Question 10

A patient is exposed to X-rays, which cause DNA damage. Which DNA repair mechanism is most likely to be activated to remove and replace damaged DNA segments?

Accepted Answer

Nucleotide excision repair

Question 11

Which of the following best describes the composition of a nucleosome?

Accepted Answer

A segment of DNA wrapped around a core of histone proteins

Question 12

If a eukaryotic cell lost the function of telomerase, what would be the most likely long-term consequence?

Accepted Answer

The chromosomes would gradually shorten with each cell division, eventually leading to loss of genetic information.

Question 13

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

Accepted Answer

One strand is synthesized continuously (leading), while the other is synthesized discontinuously (lagging).

Question 14

Which enzyme removes RNA primers and replaces them with DNA nucleotides during DNA replication?

Accepted Answer

DNA polymerase I

Question 15

A scientist observes that a DNA sample contains 30% adenine. According to Chargaff’s rules, what percentage of guanine should be present?

Accepted Answer

20%

Question 16

Which of the following best explains why DNA polymerase requires a primer to begin synthesis?

Accepted Answer

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

Question 17

Which of the following scenarios would most likely result in a mutation being passed to the next generation?

Accepted Answer

A mutation occurs in the coding region of a germ cell and is not repaired.

Question 18

Which of the following best describes euchromatin?

Accepted Answer

Loosely packed chromatin that is generally accessible for transcription.

Question 19

Which of the following is a real-world consequence of errors in DNA replication that are not corrected?

Accepted Answer

Increased genetic diversity in a population.

Question 20

Which of the following best explains why prokaryotes do not face the same end-replication problem as eukaryotes?

Accepted Answer

Prokaryotes have circular chromosomes, so they do not lose DNA from the ends during replication.

lecture 22-23: The Molecular Basis of Inheritance: DNA Structure and Replication

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