Question

Which of the following statement is most correct in DNA replication

• A. Helicase enzyme separates the two strands, DNA gyrase helps in opening of DNA double helix in front of replication fork and Tus protein helps in termination of replication
• B. DNA polymerase enzyme separates the two strands, DNA gyrase helps in opening of DNA double helix in front of replication fork and Tus protein helps in termination of replication
• C. Helicase enzyme separates the two strands, DNA ligase helps in opening of DNA double helix in front of replication fork and Tus protein helps in termination of replication
• D. DNA ligase enzyme separates the two strands, DNA gyrase helps in opening of DNA double helix in front of replication fork and topoisomerase helps in termination of replication

Hint:

Remember the three key replication enzymes and proteins: Helicase unwinds, Gyrase relieves supercoiling strain ahead of the fork, and Tus terminates replication by binding to Ter sites.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
DNA replication is a highly coordinated process that requires the sequential action of several enzymes and accessory proteins to ensure accurate duplication of the genetic material.

Step 2: Detailed Explanation:
Let us analyze the role of each enzyme mentioned in the options to determine the most accurate statement:
1. Helicase is the enzyme responsible for unwinding the double-stranded template DNA by breaking the hydrogen bonds between complementary base pairs at the replication fork.
2. DNA gyrase (a bacterial type II topoisomerase) relieves the torsional strain and positive supercoiling that accumulates in front of the advancing replication fork as the strands are separated.
3. Tus (terminus utilization substance) is a specialized protein in prokaryotes that binds to specific termination (Ter) sequences, creating a replica-trap to block the replisome and terminate replication.
Looking at the choices:
Option (A) correctly attributes strand separation to helicase, torsional relief to DNA gyrase, and replication termination to the Tus protein.
Option (B) is incorrect because DNA polymerase synthesizes new DNA strands rather than separating the template strands.
Option (C) is incorrect because DNA ligase seals nicks in the phosphodiester backbone of DNA rather than opening the double helix.
Option (D) is incorrect because DNA ligase does not separate DNA strands, and topoisomerase does not directly act as the primary protein responsible for termination in prokaryotes.

Step 3: Final Answer:
Therefore, the most accurate statement is option (A).