Which protein prevents the separated DNA strands from re-annealing during replication?

Which protein prevents the separated DNA strands from re-annealing during replication?

• A. Single-strand binding proteins
• B. DNA ligase
• C. Helicase
• D. Topoisomerase

Answer: (A)

When the DNA double helix is opened at the replication fork, exposed single-stranded DNA tends to re-anneal or degrade unless it is stabilized. Single-strand binding proteins bind to these exposed strands, coating them to keep the strands from coming back together and to protect them from nucleases. This stabilization makes the template ready for primase and DNA polymerase to copy the DNA efficiently. The other proteins have different roles: helicase is the motor that unwinds the helix but doesn’t prevent re-annealing after unwinding; topoisomerase relieves torsional stress ahead of the fork; DNA ligase seals nicks in the sugar-phosphate backbone after synthesis.

When the DNA double helix is opened at the replication fork, exposed single-stranded DNA tends to re-anneal or degrade unless it is stabilized. Single-strand binding proteins bind to these exposed strands, coating them to keep the strands from coming back together and to protect them from nucleases. This stabilization makes the template ready for primase and DNA polymerase to copy the DNA efficiently.

The other proteins have different roles: helicase is the motor that unwinds the helix but doesn’t prevent re-annealing after unwinding; topoisomerase relieves torsional stress ahead of the fork; DNA ligase seals nicks in the sugar-phosphate backbone after synthesis.