Quiz: DNA Replication Fundamentals — 9 perguntas

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

A. Ligase

B. DNA polymerase

C. Helicase

D. Primase

Answer: (C)

Explicação

Helicase is the enzyme that unwinds the DNA double helix at the replication fork, separating the two strands to allow replication to proceed. DNA polymerase synthesizes new DNA strands, ligase joins fragments, and primase synthesizes RNA primers.

2. Which enzyme is responsible for unwinding the DNA duplex during replication?

A. Helicase

B. Primase

C. DNA polymerase

D. Ligase

Answer: (A)

Explicação

Helicase unwinds the DNA at the replication fork, allowing for single strands to be accessible for copying. Primase synthesizes RNA primers, DNA polymerase extends new strands, and ligase joins fragments—none unwind DNA.

3. What is the primary difference between the leading and lagging strands during DNA replication?

A. The leading strand is synthesized in the 3' to 5' direction, and the lagging in 5' to 3'.

B. The leading strand is synthesized discontinuously, while the lagging strand is continuous.

C. The leading strand uses RNA primers, whereas the lagging strand does not.

D. The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized in fragments.

Answer: (D)

Explicação

The leading strand is synthesized continuously in the 5' to 3' direction, following the replication fork. The lagging strand is synthesized discontinuously in Okazaki fragments, also in the 5' to 3' direction, but in segments opposite to the fork movement.

4. Where does DNA replication primarily occur in eukaryotic cells?

A. In the nucleus

B. In the cytoplasm

C. In the mitochondria

D. In the endoplasmic reticulum

Answer: (A)

Explicação

DNA replication in eukaryotic cells takes place in the nucleus, while in prokaryotes, it occurs in the cytoplasm. Mitochondria have their own DNA replication, but it's not the primary location for nuclear DNA.

5. Which base pairing rule is correct in DNA replication?

A. A pairs with T, C pairs with G

B. A pairs with C, G pairs with T

C. A pairs with G, C pairs with T

D. A pairs with G, T pairs with C

Answer: (A)

Explicação

In DNA, the base pairing follows specific rules: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). These pairs are stabilized by hydrogen bonds and are essential for accurate replication.

6. What is the function of DNA ligase during replication?

A. Unwinds DNA strands

B. Synthesizes RNA primers

C. Joins Okazaki fragments

D. Proofreads DNA

Answer: (C)

Explicação

Ligase joins Okazaki fragments on the lagging strand, sealing nicks in the sugar-phosphate backbone. It does not unwind DNA, synthesize primers, or proofread.

7. How many hydrogen bonds form between adenine and thymine in DNA?

A. Two

B. Three

C. One

D. Four

Answer: (A)

Explicação

Adenine pairs with thymine via two hydrogen bonds, whereas cytosine pairs with guanine via three hydrogen bonds, reflecting their base pairing rules.

8. Which of the following best describes the directionality of DNA synthesis?

A. 3' to 5'

B. 5' to 3'

C. 5' to 5'

D. 3' to 3'

Answer: (B)

Explicação

DNA synthesis always occurs in the 5' to 3' direction, meaning nucleotides are added to the 3' end of the growing strand.

9. On which strand is DNA synthesized continuously during replication?

A. Leading strand

B. Lagging strand

C. Okazaki strand

D. Template strand

Answer: (A)

Explicação

The leading strand is synthesized continuously toward the replication fork, while the lagging strand is synthesized discontinuously in Okazaki fragments.