DP Biology (first assessment 2025)

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Question 22M.2.SL.TZ2.7b

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Date May 2022 Marks available [Maximum mark: 3] Reference code 22M.2.SL.TZ2.7b
Level SL Paper 2 Time zone TZ2
Command term Describe Question number b Adapted from N/A
b.
[Maximum mark: 3]
22M.2.SL.TZ2.7b
(b)

Describe the function of three named enzymes involved in DNA replication.

[3]

Markscheme
  1. Helicase separates/unwinds DNA from double helix;
  2. (DNA) gyrase / topoisomerase releases tension/strain (caused by super coiling);
  3. (DNA) primase builds/forms/adds an RNA primer;
  4. DNA polymerase I is a (5’ → 3’) exonuclease/removes RNA primers/replacement of RNA by DNA;
  5. DNA polymerase III synthesizes DNA (5’ → 3’) on leading/lagging strands/forms bonds between DNA nucleotides;
  6. (DNA) ligase connects/seals nick between Okazaki fragments to make continuous DNA strand;

Only mark the first three answers in sequence.

DNA polymerase I required for mpd and DNA polymerase III required for mpe (i.e., the numbers are required).

Examiners report

This question about the enzymes involved in replication was generally well done. Some omitted the I and the III for polymerase and/or focused on base pairing instead of elongation of strands with DNA polymerase III. The details around the relative role of base pairing and covalent bond formation was sometimes lacking.

Syllabus sections