DP Biology (first assessment 2025)
Question 21M.2.HL.TZ2.7b
| Date | May 2021 | Marks available | [Maximum mark: 3] | Reference code | 21M.2.HL.TZ2.7b |
| Level | HL | Paper | 2 | Time zone | TZ2 |
| Command term | Outline | Question number | b | Adapted from | N/A |
b.
[Maximum mark: 3]
21M.2.HL.TZ2.7b
(b)
Outline the role of three enzymes used in the replication of DNA.
[3]
Markscheme
a. helicase to separate/unwind DNA strands ✔
b. gyrase / toposiomerase to relax the tension as bacterial DNA is being uncoiled / prevent supercoiling ✔
c. primase to synthesise primers ✔
d. polymerase (I) removes primers and replaces with nucleotide ✔
e. polymerase (III) adds nucleotides (in a 5' to 3' direction) ✔
f. ligase joins (Okazaki) fragments together ✔
Accept the enzyme name without ‘DNA’ included; e.g. ‘DNA ligase’ or ‘ligase’ can both be accepted.
Examiners report
Well answered.
