Question

in e. coli, there is a mutation in a gene called dnab that alters the helicase that normally acts at the origin of replication. which of the following events would you expect to occur as a result of this mutation?

no proofreading will occur.

the dna strands at the origin of replication will separate, but replication will not progress.

the dna will supercoil.

dna polymerase i will not function correctly.

Explanation:

1. Recall the function of helicase (encoded by dnaB in E. coli) in DNA replication: Helicase unwinds the DNA double helix at the origin of replication to separate the strands and allow replication machinery to proceed.
2. Analyze each option:

• "No proofreading will occur": Proofreading is done by DNA polymerases, not helicase, so this is incorrect.
• "The DNA strands at the origin of replication will separate, but replication will not progress": If the mutated helicase can still separate the strands (partially or initially) but fails to function properly to allow replication to proceed (e.g., can't maintain unwinding or interact with other replication proteins), this is plausible.
• "The DNA will supercoil": Supercoiling is managed by topoisomerases, not helicase, so this is incorrect.
• "DNA polymerase I will not function correctly": DNA polymerase I function is independent of helicase (in terms of direct interaction for its core function), so this is incorrect.

Answer:

The DNA strands at the origin of replication will separate, but replication will not progress.