QCE Biology — Unit 4
DNA Replication — Flashcards & Quiz
DNA replication is the semi-conservative copying of the genome and a core QCE Biology Unit 4 concept. You need to name the key enzymes, explain why leading and lagging strand synthesis differ, and describe how proofreading maintains fidelity. The Meselson-Stahl experiment provides the classic evidence that replication is semi-conservative, and is a favourite exam context.
Sample Flashcards
Q1: Outline the process of semi-conservative DNA replication.
Helicase unwinds the double helix and breaks hydrogen bonds between base pairs, forming a replication fork. DNA polymerase III adds complementary nucleotides to each template strand in the 5' to 3' direction. The leading strand is synthesised continuously; the lagging strand is synthesised in Okazaki fragments joined by DNA ligase. Each new molecule contains one original and one new strand (semi-conservative).
Sample Quiz Questions
Q1: DNA replication is described as semi-conservative because each new DNA molecule contains one original strand and one new strand.
Answer: TRUE
Semi-conservative means each daughter molecule retains (conserves) one of the original parent strands and pairs it with a newly synthesised complementary strand.
Q2: DNA polymerase can add nucleotides in both the 5' to 3' and 3' to 5' directions.
Answer: FALSE
DNA polymerase can ONLY add nucleotides in the 5' to 3' direction. This is why the lagging strand must be synthesised in short Okazaki fragments.
Last updated: March 2026 · 1 flashcards · 2 quiz questions