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CAIE A Level Biology 9700 · Nucleic acids and protein synthesis

Nucleic acids and protein synthesis: outline question

Outline5 marksStandard

A DNA replication fork has the following features:

  • Two parental DNA strands: Strand X (running 3' to 5' towards the fork) and Strand Y (running 5' to 3' towards the fork).
  • Newly synthesized strands: a continuous Leading strand on Strand X and a discontinuous Lagging strand made of fragments on Strand Y.
  • Enzymes: DNA polymerase is shown on both the leading and lagging strands; DNA ligase is shown joining the fragments on the lagging strand.
  • The 5' and 3' ends are marked on all strands, and the fork moves from left to right.

Outline the process of semi-conservative DNA replication that occurs during the S phase of the cell cycle. In your answer, refer to these features and explain the roles of DNA polymerase and DNA ligase.

0 words · 5 marks

No account needed for your first marks. Your answer is used only to mark it.

How this question is marked

5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.

Outline means: Give the main points briefly. Less detail than describe, but every key step has to be there. One short line per step, in order. The marks are for coverage, not depth.

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