Question 1

Which of the following best describes the structure of a DNA molecule as shown in the images above?

Accepted Answer

A double helix with antiparallel strands held together by hydrogen bonds between complementary bases

Question 2

What type of bond connects the nucleotides in the backbone of a DNA strand?

Accepted Answer

Phosphodiester bond

Question 3

Which carbon of the deoxyribose sugar is the phosphate group attached to in a nucleotide?

Accepted Answer

5' carbon

Question 4

If a DNA sample contains 20% adenine, what is the percentage of guanine in the sample?

Accepted Answer

$$30\%$$

Question 5

Which enzyme is responsible for unwinding the DNA double helix during replication?

Accepted Answer

Helicase

Question 6

During DNA replication, which enzyme synthesizes the RNA primer required for DNA polymerase to begin synthesis?

Accepted Answer

Primase

Question 7

What is the main difference between the leading and lagging strands during DNA replication?

Accepted Answer

The leading strand is synthesized continuously, while the lagging strand is synthesized in short fragments.

Question 8

Which model of DNA replication was supported by the Meselson-Stahl experiment?

Accepted Answer

Semiconservative

Question 9

What is the function of DNA ligase during DNA replication?

Accepted Answer

It joins Okazaki fragments on the lagging strand.

Question 10

Why does DNA polymerase synthesize DNA only in the 5' to 3' direction?

Accepted Answer

Because the 3' end provides a free hydroxyl group for nucleotide addition and proofreading is more efficient in this direction.

Question 11

Which of the following best explains why telomeres are important in eukaryotic chromosomes?

Accepted Answer

They prevent the loss of essential genes during DNA replication.

Question 12

A hereditary defect in which DNA repair mechanism is associated with a form of colon cancer?

Accepted Answer

Mismatch repair

Question 13

Which enzyme relieves the strain caused by tight twisting ahead of the replication fork?

Accepted Answer

Topoisomerase

Question 14

What is the role of single-strand binding proteins during DNA replication?

Accepted Answer

They stabilize unwound DNA strands and prevent them from reannealing.

Question 15

Which of the following is a correct sequence of events in the Meselson-Stahl experiment?

Accepted Answer

Grow cells in $$^{15}N$$, shift to $$^{14}N$$, extract DNA, centrifuge in cesium chloride

Question 16

Which repair mechanism removes only the damaged base from DNA?

Accepted Answer

Base excision repair

Question 17

What is the function of telomerase in eukaryotic cells?

Accepted Answer

It extends telomeres to prevent chromosome shortening in germ line and some stem cells.

Question 18

Which of the following statements about Okazaki fragments is TRUE?

Accepted Answer

They are joined together by DNA ligase after RNA primers are replaced with DNA.

Question 19

Which of the following best explains why errors in DNA replication are rare?

Accepted Answer

DNA polymerases have proofreading activity and can replace incorrect nucleotides.

Question 20

Which of the following is a direct result of the semiconservative model of DNA replication?

Accepted Answer

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

DNA Structure and Replication: Foundations and Mechanisms

Study Guide - Practice Questions