Cuestionario: Fundamentals of DNA Replication — 9 preguntas

1. What is the structure of DNA characterized by?

A. A single strand of nucleotides forming a linear chain

B. A double helix composed of two antiparallel strands with complementary base pairing

C. A flat, sheet-like structure stabilized by hydrogen bonds

D. A triple helix with three strands intertwined

Answer: (B)

Explicación

DNA's structure is characterized by a double helix formed by two antiparallel strands. These strands are composed of nucleotides linked by phosphodiester bonds, with nitrogenous bases pairing specifically (A with T, C with G) via hydrogen bonds. This structure was discovered by Watson and Crick in 1953 and is fundamental to its function in storing genetic information.

2. What is the primary function of helicase during DNA replication?

A. To synthesize RNA primers needed for DNA replication

B. To unwind the DNA double helix by breaking hydrogen bonds between bases

C. To join Okazaki fragments on the lagging strand

D. To synthesize the new DNA strand in the 3' to 5' direction

Answer: (B)

Explicación

Helicase unwinds the DNA double helix by breaking hydrogen bonds between base pairs, creating the replication fork. The synthesis of primers is performed by primase, not helicase.

3. Which enzyme is responsible for unwinding the DNA double helix at the replication fork during DNA replication?

A. DNA polymerase

B. Helicase

C. Primase

D. Ligase

Answer: (B)

Explicación

Helicase is the enzyme responsible for unwinding the DNA double helix at the replication fork by breaking hydrogen bonds between base pairs. This unwinding creates the single-stranded DNA templates needed for replication. DNA polymerase synthesizes new DNA strands, primase synthesizes RNA primers, and ligase joins Okazaki fragments; none of these enzymes unwind DNA.

4. Which enzyme is responsible for synthesizing the RNA primers during DNA replication?

A. DNA polymerase

B. Ligase

C. Primase

D. Helicase

Answer: (C)

Explicación

Primase synthesizes RNA primers necessary to start DNA replication on both leading and lagging strands, providing a starting point for DNA polymerase.

5. What is the primary role of replication enzymes during DNA replication?

A. To facilitate the unwinding, synthesis, and sealing of DNA strands, ensuring accurate copying of genetic information.

B. To regulate gene expression by controlling the transcription process.

C. To package DNA into chromosomes for cell division.

D. To repair damaged DNA by excising and replacing faulty nucleotides.

Answer: (A)

Explicación

Replication enzymes work together to unwind the DNA helix, synthesize new complementary strands, and join fragments to ensure accurate duplication of genetic material. This collective function is essential for DNA replication, which is fundamental for cell division and genetic inheritance.

6. Why are Okazaki fragments necessary on the lagging strand?

A. Because DNA polymerase can only synthesize DNA in the 5' to 3' direction, requiring discontinuous synthesis on the lagging strand

B. To allow the lagging strand to be synthesized in the same direction as the leading strand

C. Because the lagging strand is a continuous DNA segment

D. To prevent the DNA from unwinding during replication

Answer: (A)

Explicación

Okazaki fragments are short DNA segments synthesized discontinuously on the lagging strand because DNA polymerase synthesizes DNA only in the 5' to 3' direction, opposite the movement of the replication fork.

7. What is the role of DNA ligase in replication?

A. To unwind the DNA double helix at the replication fork

B. To synthesize the RNA primers

C. To join Okazaki fragments into a continuous DNA strand

D. To synthesize the new DNA strand in the 5' to 3' direction

Answer: (C)

Explicación

DNA ligase joins Okazaki fragments together, sealing the nicks to create a continuous DNA strand on the lagging template.

8. In what year did Watson and Crick publish their discovery of the DNA double helix?

A. 1953

B. 1947

C. 1961

D. 1928

Answer: (A)

Explicación

Watson and Crick published their paper describing the structure of DNA as a double helix in 1953, which was a groundbreaking event in molecular biology.

9. What is the significance of the antiparallel nature of DNA strands?

A. It allows for complementary base pairing and proper enzyme function during replication and transcription

B. It prevents the hydrogen bonds from forming between bases

C. It is necessary for the DNA strands to run in the same direction

D. It causes the DNA to be resistant to denaturation

Answer: (A)

Explicación

The antiparallel orientation facilitates complementary base pairing and is essential for the proper function of enzymes involved in replication and transcription, as they read the DNA in specific directions.