This free quiz has 12 real AQA A-level Biology exam questions on protein synthesis (27 marks, about 35 minutes). It marks itself: the tick-box question is marked for you, and for written answers you check your work against the real AQA mark scheme.
What the quiz covers (AQA 3.4.2)
the function of ribosomes
where transcription happens in a eukaryotic cell
naming the parts of a tRNA molecule
how mRNA is obtained from pre-mRNA, and how this differs in prokaryotes
working out DNA and mRNA base sequences, and using a codon table
how RNA polymerase joins RNA nucleotides
the role of tRNA, and structural differences between mRNA and tRNA
describing transcription (5 marks) and the roles of ribosomes, tRNA and ATP in translation (6 marks)
How to use it
Write each answer in full before you open the mark scheme. For the long answers, set out transcription and translation as a sequence of steps and name the molecule doing each job. For the mRNA and tRNA question, write each difference as a matched pair (mRNA … whereas tRNA …).
Where students lose marks (from AQA examiners’ reports and mark schemes)
Each point below is followed by wording that gained marks.
A specific amino acid. Many students wrote that tRNA brings “an amino acid”. Without saying it is a specific amino acid, the mark wasn't given.
✔ Gains credit: tRNA brings a specific amino acid, the one coded for by the codon.
Anticodons bind to codons. General descriptions of complementary base pairing were common, but many answers left out the idea of binding, or didn't say the codon and anticodon are complementary.
✔ Gains credit: the anticodon on a tRNA molecule binds to the complementary codon on the mRNA.
Comparing mRNA and tRNA. Examiners saw many misconceptions, such as tRNA being double-stranded or containing thymine or exons. Many compared “single-stranded” mRNA with cloverleaf tRNA, described mRNA as shorter, or wrote “tRNA has an amino acid”.
✔ Gains credit: matched pairs, e.g. mRNA is linear whereas tRNA is a folded cloverleaf with hydrogen-bonded base pairs; mRNA has no amino acid binding site whereas tRNA has one.
What RNA polymerase joins. Many students described bonds forming between bases or between RNA and DNA, or said RNA polymerase forms hydrogen bonds or joins complementary bases. These were rejected.
✔ Gains credit: RNA polymerase joins adjacent RNA nucleotides by condensation reactions, forming phosphodiester bonds.
Describe splicing, don't just name it. Some answers simply said “pre-mRNA is spliced” without describing what happens. Vague references to changes in the “code”, rather than the base sequence, weren't credited.
✔ Gains credit: introns are removed and exons are joined to form mRNA; splicing errors change the base sequence of the exons, or delete exons.
Prokaryotes have no introns. In one question 58% scored 0. Students wrote that only eukaryotes make mRNA in a nucleus, or wrongly said prokaryotes have single-stranded DNA, mistaking a single loop of DNA for a single strand.
✔ Gains credit: only eukaryotes produce pre-mRNA that is spliced to remove introns, because prokaryotic DNA has no introns.
The roles of ATP. Few students mentioned that ATP is used when an amino acid attaches to tRNA, and the use of ATP in forming peptide bonds was rarely seen.
✔ Gains credit: ATP provides the energy for an amino acid to attach to its tRNA and for peptide bonds to form.
Keep practising
The other AQA 3.4 self-marking quizzes: DNA, genes and chromosomes · Mutation and meiosis · Natural selection · Species and biodiversity
Topic 3.3 quizzes start with surface area to volume ratio
DNA and protein synthesis: common questions and mark scheme insights
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.