5. The diagram shows the process of DNA replication at a replication fork.
[VISUALIZATION: Diagram of a DNA replication fork. Show the parent DNA double helix unwinding. Label the leading strand being synthesized continuously towards the fork and the lagging strand being synthesized discontinuously away from the fork in Okazaki fragments. Label Helicase, DNA Polymerase III, RNA primer, Okazaki fragment, and indicate the 5′ and 3′ ends of the parent strands and newly synthesized strands to show directionality.]
(a) State the function of helicase in DNA replication. [1]
(b) Distinguish between the synthesis of the leading strand and the lagging strand using **two** features. [2]
(c) Explain the role of complementary base pairing in ensuring the fidelity of DNA replication. [2]
Question
State the function of helicase in DNA replication. [1]
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What enzyme is responsible for separating the two DNA strands at the start of replication?
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Unwinds/unzips the DNA double helix / breaks hydrogen bonds between bases.
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Distinguish between the synthesis of the leading strand and the lagging strand using **two** features. [2]
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Consider how DNA polymerase works (5′ to 3′ synthesis) and the antiparallel nature of DNA strands. Think about continuity and direction.
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1. Leading strand synthesized continuously, lagging strand discontinuously/in fragments. 2. Leading strand synthesized towards the replication fork, lagging strand synthesized away from the fork. (Also acceptable: Lagging strand needs multiple primers, leading needs one).
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Explain the role of complementary base pairing in ensuring the fidelity of DNA replication. [2]
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Recall the specific base pairing rules (A with T, C with G). How does this rule guide the addition of new nucleotides during replication?
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A pairs only with T, and C pairs only with G. Each parent strand acts as a template, ensuring the new strand has a complementary sequence, thus maintaining fidelity.
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