This free quiz has 12 real AQA A-level Biology exam questions on DNA, RNA and DNA replication (24 marks, about 30 minutes). It marks itself: for each answer you check your work against the real AQA mark scheme and tick the points you made.
What the quiz covers (AQA 3.1.5)
the structure of DNA and RNA nucleotides
the bonds in a DNA molecule
what ribosomes are made of
the scientists behind the models of DNA structure and replication
the roles of DNA helicase and DNA polymerase
how phosphodiester bonds form
a calculation from base pairing
the evidence for semi-conservative replication, and describing the process (5 marks)
How to use it
Write each answer in full before you open the mark scheme. Use full names (adenine, not A), and for DNA vs RNA comparisons write matched pairs, e.g. DNA … whereas RNA ….
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
Full base names. Students wrote the bases as letters (A, T, C, G, U). Examiners didn't credit letters alone, even when the idea was right.
✔ Gains credit: the full names adenine, thymine, cytosine, guanine and uracil, e.g. thymine in DNA and uracil in RNA.
Paired DNA–RNA comparisons. Some gave a fact about only one molecule. “Helix” on its own, without saying DNA is a double helix, wasn't credited.
✔ Gains credit: matched pairs, e.g. DNA is double-stranded and RNA is single-stranded; DNA has deoxyribose and RNA has ribose.
Parts of a nucleotide. Students labelled the sugar “pentose” instead of deoxyribose, or wrote “phosphorus” instead of phosphate.
✔ Gains credit: a DNA nucleotide is made of deoxyribose, a phosphate group and a named nitrogenous base.
What ribosomes contain. Many students couldn't name what a ribosome is made of, and some said tRNA or mRNA. Only 18% gained both marks in one paper.
✔ Gains credit: ribosomes are made of ribosomal RNA (rRNA) and protein.
DNA helicase. Students said helicase just “unzips” DNA without mentioning hydrogen bonds, or said it “hydrolyses” hydrogen bonds, which was rejected.
✔ Gains credit: DNA helicase breaks the hydrogen bonds between complementary bases, so the two strands separate.
DNA polymerase. The most common mistake was saying DNA polymerase forms hydrogen bonds or joins complementary bases.
✔ Gains credit: DNA polymerase joins adjacent DNA nucleotides by condensation reactions, forming phosphodiester bonds.
Templates and semi-conservative. Very few students said the template decides the order of the new nucleotides.
✔ Gains credit: both strands act as templates; the order of bases on the template determines the order of nucleotides in the new strand; each new molecule has one original and one new strand.
Keep practising
The other AQA 3.1 self-marking quizzes: Carbohydrates · Lipids · Proteins · Enzymes · ATP, water and ions
The AQA topic index
weekly AQA group classes: Year 12 on Tuesdays at 5.15pm, Year 13 on Wednesdays or Thursdays at 6.30pm
Questions © AQA, from past A-level and AS Biology papers, with their mark schemes and examiners’ reports.