QCM : Fundamentals of DNA Replication — 9 questions

Questions et réponses du QCM

1. What is the structure of DNA characterized by?

A single strand of nucleotides forming a linear chain
A double helix composed of two antiparallel strands with complementary base pairing
A flat, sheet-like structure stabilized by hydrogen bonds
A triple helix with three strands intertwined

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

Explication

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?

To synthesize RNA primers needed for DNA replication
To unwind the DNA double helix by breaking hydrogen bonds between bases
To join Okazaki fragments on the lagging strand
To synthesize the new DNA strand in the 3' to 5' direction

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

Explication

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?

DNA polymerase
Helicase
Primase
Ligase

Helicase

Explication

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?

DNA polymerase
Ligase
Primase
Helicase

Primase

Explication

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?

To facilitate the unwinding, synthesis, and sealing of DNA strands, ensuring accurate copying of genetic information.
To regulate gene expression by controlling the transcription process.
To package DNA into chromosomes for cell division.
To repair damaged DNA by excising and replacing faulty nucleotides.

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

Explication

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?

Because DNA polymerase can only synthesize DNA in the 5' to 3' direction, requiring discontinuous synthesis on the lagging strand
To allow the lagging strand to be synthesized in the same direction as the leading strand
Because the lagging strand is a continuous DNA segment
To prevent the DNA from unwinding during replication

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

Explication

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?

To unwind the DNA double helix at the replication fork
To synthesize the RNA primers
To join Okazaki fragments into a continuous DNA strand
To synthesize the new DNA strand in the 5' to 3' direction

To join Okazaki fragments into a continuous DNA strand

Explication

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?

1953
1947
1961
1928

1953

Explication

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?

It allows for complementary base pairing and proper enzyme function during replication and transcription
It prevents the hydrogen bonds from forming between bases
It is necessary for the DNA strands to run in the same direction
It causes the DNA to be resistant to denaturation

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

Explication

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.

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DNA double helix — structure?

Two antiparallel strands with base pairing.

DNA — structure?

Double helix, two antiparallel strands.

Replication fork — role?

Site where DNA unwinds for replication.

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