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Module 5: Heredity
Quick questions on DNA replication explained: HSC Biology Module 5
9short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is the Watson and Crick model?Show answer
DNA is a double helix of two antiparallel strands held together by hydrogen bonds between complementary base pairs. Adenine pairs with thymine (A-T) by two hydrogen bonds. Guanine pairs with cytosine (G-C) by three hydrogen bonds. Each strand has a 5' end and a 3' end; the two strands run in opposite directions (antiparallel).
What is the four steps?Show answer
1. Unwinding. The enzyme helicase breaks the hydrogen bonds between base pairs, separating the double helix into two single strands at the replication fork.
What is 1. Unwinding?Show answer
The enzyme helicase breaks the hydrogen bonds between base pairs, separating the double helix into two single strands at the replication fork.
What is 2. Priming?Show answer
Primase synthesises a short RNA primer on each single strand, giving DNA polymerase a free 3'-OH group to extend from.
What is 3. Elongation?Show answer
DNA polymerase reads each template strand in the 3' to 5' direction and adds complementary free nucleotides to the growing daughter strand in the 5' to 3' direction.
What is 4. Ligation?Show answer
DNA ligase joins the Okazaki fragments into one continuous strand.
What is forgetting the antiparallel orientation?Show answer
DNA polymerase only works in the 5' to 3' direction. This is why the lagging strand needs Okazaki fragments.
What is confusing primase and ligase?Show answer
Primase makes the primer; ligase joins fragments. Markers test this regularly.
What is wrong base pairs?Show answer
A pairs with T (DNA) or U (RNA). G pairs with C. Get this wrong and you lose 1-2 marks immediately.