Function of DNA Helicase In DNA metabolism, what is the primary role of DNA helicase?
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AUnwind the double helix by separating complementary strands
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BBind the double helix more tightly to prevent unwinding
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CBreak phosphodiester bonds to excise nucleotides
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DNone of the above
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EJoin adjacent DNA fragments to seal nicks
Answer
Correct Answer: Unwind the double helix by separating complementary strands
Explanation
Introduction / Context:Helicases are essential nucleic acid motor proteins in replication, repair, and recombination. They use NTP hydrolysis to destabilize base pairing and unwind DNA for downstream enzymes.
Given Data / Assumptions:
- Helicase acts ahead of replication forks.
- Strand separation is prerequisite for polymerase action.
Concept / Approach:Differentiate unwinding (helicase) from nick sealing (ligase) and backbone cleavage (nucleases). Helicase does not cut phosphodiester bonds; it disrupts hydrogen bonding between bases through mechanical translocation and energy usage.
Step-by-Step Solution:
Step 1: Identify the process requiring strand separation.Step 2: Map to helicase function (unwinding).Step 3: Exclude nuclease and ligase activities.Verification / Alternative check:In vitro helicase assays measure duplex unwinding; ligase shows nick sealing without unwinding capability.
Why Other Options Are Wrong:
- Tight interaction to prevent unwinding: opposite of helicase action.
- Breaking phosphodiester bonds: nuclease, not helicase.
- Joining fragments: ligase function.
Common Pitfalls:Confusing unwinding (hydrogen bonds) with cutting (phosphodiester bonds).
Final Answer:Unwind the double helix by separating complementary strands