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CAIE A Level Biology 9700 · Nucleic acids and protein synthesis

Nucleic acids and protein synthesis: outline question

Outline5 marksStandard

A researcher studied DNA replication in bacteria. Bacteria were grown in a medium containing heavy nitrogen (¹⁵N) for many generations so that all DNA contained ¹⁵N. They were then transferred to a medium containing light nitrogen (¹⁴N). After one round of replication, the extracted DNA had a density exactly halfway between heavy and light DNA. After two rounds, two DNA bands were observed: one intermediate density and one light density.

Outline the process of semi-conservative replication as revealed by this experiment. In your answer, you should refer to:

  • the structure of DNA
  • the roles of DNA polymerase and DNA ligase
  • why the lagging strand is synthesized discontinuously
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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