What this practice covers
These questions are drawn from past CIE 9700 Biology papers and filtered to structure of nucleic acids and replication of dna. You answer, you find out immediately whether you were right, and you get the reasoning for the correct option and for each distractor. Wrong answers go to a mistakes locker so you can come back to exactly those.
Practice is free. You need an account only so your progress and your mistakes are still there next time.
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What examiners see students get wrong here
These are the errors that cost marks on structure of nucleic acids and replication of dna, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Saying helicase "unzips the DNA" without naming the hydrogen bonds it breaks.
- Saying DNA polymerase joins bases. It forms phosphodiester bonds between the sugar and phosphate.
- Applying Chargaff's rule to RNA or to a single strand.
- Saying replication is semi-conservative "because half the DNA is conserved". Each molecule keeps one whole original strand.
- Saying every mutation changes the protein. A substitution in a degenerate position changes nothing.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Structure of nucleic acids and replication of DNA revision notes.