QUESTION 23 (6 marks)
a) Identify two enzymes involved in DNA replication and describe their functions.
[4 marks]
Enzyme 1:
Function:
Enzyme 2:
Function:
b) Explain how synthesis of the leading strand is different from the lagging strand.
[2 marks]
QCAA guide · typeset solution
QCAA sample response and mark allocation
23a) | Enzyme 1: Helicase Function: Helicase unwinds the double helix and separates the strands. Enzyme 2: DNA polymerase Function: DNA polymerase forms new complementary strands by adding nucleotides using the base pairing rules. | • identifies an enzyme involved in DNA replication [1 mark] • describes the function of this enzyme [1 mark] • identifies a second enzyme involved in DNA replication [1 mark] • describes the function of the second enzyme [1 mark] |
23b) | Synthesis of the leading strand is continuous, whereas synthesis of the lagging strand occurs in segments, creating Okazaki fragments which must later be joined. | • explains that synthesis of the leading strand is continuous [1 mark] • explains that synthesis of the lagging strand is non-continuous [1 mark] |
QCAA sample response and marking criteria reproduced from the official guide.
Compare your working with the guide above.