Once the DNA at the replication fork is unwound by helicases, what prevents the two strands from coming back together to re-form a double helix?

• A. The helicase modifies the DNA in such a way as to eliminate the affinity between the two strands.
• B. DNA polymerase follows the helicase so closely that there is no chance for the strands to come back together.
• C. The helicase pushes the two strands so far apart that they have no chance of finding each other.
• D. One of the strands is rapidly degraded, preventing the double helix from re-forming.
• E. Single-strand binding proteins bind the unwound DNA and prevent the double helix from re-forming.

Answer: (E)

Verified step by step guidance

1. Understand the role of helicase: Helicase is an enzyme that unwinds the DNA double helix at the replication fork, separating the two strands to allow replication to occur.
2. Identify the problem: Once the DNA strands are separated, they have a natural tendency to re-anneal or come back together due to complementary base pairing.
3. Consider the options: Evaluate each given option to determine which mechanism actually prevents the re-formation of the double helix.
4. Recognize the role of single-strand binding proteins: These proteins bind to the separated DNA strands, stabilizing them and preventing them from re-annealing.
5. Conclude with the correct mechanism: Single-strand binding proteins are crucial in maintaining the separation of DNA strands during replication, ensuring that the replication process can proceed efficiently.