DNA and Protein Synthesis: AQA A Level Biology Exam Questions by Topic

AQADNA and Protein SynthesisExam Questions
Written by Tom Whitburn

DNA and protein synthesis (AQA 3.4.2) is where the genetic code turns into real proteins, and it turns up on almost every AS and A-level paper, often as a 5- or 6-mark description. You need to define the genome and the proteome, compare the structure of mRNA and tRNA, describe transcription and the role of RNA polymerase, explain how pre-mRNA is spliced in eukaryotes but not in prokaryotes, describe translation with the roles of ribosomes, tRNA and ATP, and use a codon table to link base sequences to amino acids.

The examiners' reports show the same slips every year. Students define the proteome as 'all the proteins in a cell' instead of the proteins a cell can produce, say the genome belongs to a species, write that RNA polymerase joins complementary bases or forms hydrogen bonds, describe transcription when the question asks only for translation, forget that tRNA carries a specific amino acid, and think prokaryotic DNA is single-stranded.

Start with the definitions and RNA structure, then transcription and splicing, then translation, and finish with the codon tables and the experimental data. Answer each question on paper before you open the mark scheme. If you'd like help with this topic, my AQA masterclasses run online on Tuesdays at 5.15pm for Year 12 and on Wednesdays or Thursdays at 6.30pm for Year 13.

What you need from GCSE and Year 12

Each question on this page assumes you're secure on these GCSE and Year 12 ideas. If any of them feels shaky, revise it before you start.

  • GCSE: a gene codes for a particular sequence of amino acids, and proteins are made on ribosomes in the cytoplasm.
  • Year 12 (AQA 3.1.5.1): an RNA nucleotide has ribose, a phosphate group and one of the bases adenine, uracil, cytosine or guanine, and nucleotides are joined by phosphodiester bonds.
  • Year 12 (AQA 3.4.1): a triplet of DNA bases codes for a specific amino acid, the genetic code is degenerate, and genes contain exons separated by introns.
  • Year 12 (AQA 3.1.4.1): amino acids join by peptide bonds in condensation reactions, and the primary structure determines the tertiary structure.
  • Year 12 (AQA 3.1.6): ATP is hydrolysed to release energy for energy-requiring reactions in cells.

Key terms

These words come up in the questions and mark schemes. Examiners expect you to use them exactly.

  • Genome: the complete set of genes in a cell.
  • Proteome: the full range of proteins that a cell is able to produce.
  • Codon: a sequence of three bases on mRNA that codes for a specific amino acid.
  • Anticodon: the three bases on a tRNA molecule that are complementary to a codon on mRNA.
  • Transcription: the production of mRNA from DNA, using one DNA strand as a template.
  • RNA polymerase: the enzyme that joins RNA nucleotides by phosphodiester bonds during transcription.
  • Pre-mRNA: the RNA made by transcription in eukaryotes, which still contains introns.
  • Splicing: removing introns from pre-mRNA and joining the exons to form mRNA.
  • Translation: the production of a polypeptide from the sequence of codons carried by mRNA, at a ribosome.
  • Peptide bond: the bond formed between amino acids in a condensation reaction, using energy from ATP during translation.

What these questions cover (AQA 3.4.2)

The questions test these statements from the AQA AS and A-level Biology specification (7401/7402):

  • Genome and proteome: The concept of the genome as the complete set of genes in a cell and of the proteome as the full range of proteins that a cell is able to produce.
  • mRNA and tRNA: The structure of molecules of messenger RNA (mRNA) and of transfer RNA (tRNA).
  • Transcription: Transcription as the production of mRNA from DNA. The role of RNA polymerase in joining mRNA nucleotides.
  • Transcription: In prokaryotes, transcription results directly in the production of mRNA from DNA. (the adenovirus question asks how the hybrid DNA would look with prokaryotic DNA)
  • Transcription: In eukaryotes, transcription results in the production of pre-mRNA; this is then spliced to form mRNA.
  • Translation: Translation as the production of polypeptides from the sequence of codons carried by mRNA. The roles of ribosomes, tRNA and ATP.
  • Students should be able to: relate the base sequence of nucleic acids to the amino acid sequence of polypeptides, when provided with suitable data about the genetic code (each question gives you the codons you need; you don't have to learn which codon codes for which amino acid)
  • Students should be able to: interpret data from experimental work investigating the role of nucleic acids.

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.3 minutes per mark: the 18 questions are worth 39 marks, so about 51 minutes in total. Then mark your answer strictly against the mark scheme and read the examiners' tip underneath it. If you'd rather print the questions, download the PDF pack.

Genome and proteome (3.4.2)

Question 1

A level Paper 1 · June 2023 · Q06.1 · 2 marks · Medium

Define genome and proteome.

Question text: define genome and proteome, with a space for each, 2 marks.
Show the mark scheme Mark scheme: genome, the complete set of genes or all the DNA in a cell; proteome, the full range of proteins that a cell can produce or that its DNA codes for. Reject all the DNA or genes in a species; 'number of proteins' unqualified not accepted.

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From the examiners' report: 70% knew at least one definition. 'All the genetic information' doesn't score for genome, and for proteome you must say the proteins a cell can produce, not just the proteins in a cell.

Question 2

AS Paper 1 · November 2020 · Q09.1 · 2 marks · Hard

Explain how the proteome of a genetically modified tobacco cell differs from a control cell.

Passage about aquaporins: scientists inserted a gene from a different species into tobacco plant cells, increasing transcription of the aquaporin gene PIP1b; question asks how the proteome of a modified cell differs from that of an unmodified cell, 2 marks.
Show the mark scheme Mark scheme: the gene from a different species is expressed; so there is a new, one more, protein in the range of proteins.

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From the examiners' report: Few students saw that adding a gene from another species means one new protein is expressed. Link the proteome to the range of proteins, not just to more aquaporins.

mRNA and tRNA (3.4.2)

Question 3

AS Paper 1 · June 2018 · Q07.2 · 2 marks · Easy

Give two structural differences between mRNA and tRNA.

Question text: give two structural differences between a molecule of messenger RNA and a molecule of transfer RNA, 2 marks.
Show the mark scheme Mark scheme, any two, comparative: mRNA has no hydrogen bonds or base pairing, tRNA does; mRNA linear, tRNA clover leaf; mRNA has no amino acid binding site; mRNA has more nucleotides; mRNAs vary in length, tRNAs similar; mRNA has codons, tRNA an anticodon.

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From the examiners' report: Generally well answered. Write each difference as a clear comparison, such as 'tRNA is clover leaf, mRNA is linear'. tRNA isn't double-stranded.

Question 4

AS Paper 1 · June 2019 · Q01.3 · 1 mark

Name the structures labelled W and X on a tRNA molecule.

Figure 1: a clover-leaf tRNA molecule with W labelled at the single-stranded end at the top and X labelled at the three bases CUC on the bottom loop; question asks for the names of W and X, 1 mark.
Show the mark scheme Mark scheme: W, amino acid binding site; X, anticodon. Both needed; the idea of a binding site is needed for W.

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From the examiners' report: No examiners' report for this paper. The mark scheme wants 'amino acid binding site' for W, not just 'amino acid', and 'anticodon' for X.

Transcription and splicing (3.4.2)

Question 5

AS Paper 2 · June 2024 · Q04.1 · 1 mark · Easy

State where transcription occurs in a eukaryotic cell.

Question text: where does transcription occur in a eukaryotic cell, 1 mark.
Show the mark scheme Mark scheme: nucleus.

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From the examiners' report: Most got this. Ribosomes and rough endoplasmic reticulum are where translation happens, not transcription.

Question 6

A level Paper 1 · November 2020 · Q10.1 · 5 marks

Describe how mRNA is formed by transcription in eukaryotes.

Question text: describe how mRNA is formed by transcription in eukaryotes, 5 marks.
Show the mark scheme Mark scheme, max 5: hydrogen bonds between DNA bases break; only one strand is a template; free RNA nucleotides align by complementary base pairing; uracil pairs with adenine; RNA polymerase joins adjacent nucleotides; by phosphodiester bonds; pre-mRNA is spliced or introns removed. Reject hydrolysing hydrogen bonds.

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From the examiners' report: Say RNA nucleotides and RNA polymerase. Marks were lost for writing that RNA polymerase forms hydrogen bonds, pairs complementary bases or joins bases rather than nucleotides.

Question 7

A level Paper 1 · June 2025 · Q02.1 · 1 mark

Describe how mRNA is obtained from pre-mRNA.

Question text: describe how mRNA is obtained from pre-mRNA, 1 mark.
Show the mark scheme Mark scheme: introns removed (and exons joined). Accept a description of non-coding DNA for introns.

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From the examiners' report: Most said introns are removed. 'Pre-mRNA is spliced' on its own was too vague: say what splicing removes.

Question 8

A level Paper 1 · June 2025 · Q02.2 · 2 marks

Describe how RNA polymerase joins RNA nucleotides.

Question text: describe how RNA polymerase joins RNA nucleotides, 2 marks.
Show the mark scheme Mark scheme: phosphodiester bond; by condensation reaction. Reject a phosphodiester bond between the wrong molecules, such as between complementary bases.

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From the examiners' report: A good discriminator. Name phosphodiester bonds between adjacent nucleotides, formed by condensation; bonds between bases, or hydrogen bonds, don't score.

Question 9

AS Paper 2 · June 2022 · Q01.3 · 2 marks · Hard

Suggest how an artificial nucleic acid that binds to DNA reduces transcription.

Question text: a short, single-stranded artificial nucleic acid called PNA binds to a small section of DNA, and cells containing PNA produced less mRNA; suggest how PNA affected transcription, 2 marks.
Show the mark scheme Mark scheme: PNA is complementary to DNA or forms base pairs with it; preventing RNA polymerase binding or activity, or preventing RNA nucleotides binding, so reducing transcription.

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From the examiners' report: Only 2% got both marks. Use the stem: PNA pairs with the DNA, so RNA polymerase or RNA nucleotides can't bind there. Helicase isn't the point.

Question 10

A level Paper 3 · June 2022 · Q04.3 · 1 mark · Hard

Suggest and explain one reason why bacteria might not be able to produce every human protein.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question text: recombinant DNA technology transfers fragments of human DNA into bacteria to produce human proteins; suggest and explain one reason why bacteria might not be able to produce every human protein, 1 mark.
Show the mark scheme Mark scheme, one of: cannot splice pre-mRNA, so cannot remove introns; no Golgi apparatus, so cannot modify proteins; no transcription factors, so cannot produce mRNA.

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From the examiners' report: Only 10% scored. You must suggest and explain: 'bacteria can't splice' needs 'so the introns can't be removed'. Bacteria do have thymine and amino acids.

Translation (3.4.2)

Question 11

AS Paper 1 · June 2018 · Q07.3 · 5 marks · Medium

Starting with mRNA in the cytoplasm, describe how translation produces a polypeptide.

Question text: starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide; do not include transcription and splicing, 5 marks.
Show the mark scheme Mark scheme, max 5: mRNA associates with a ribosome; ribosome moves to the start codon; tRNA brings a specific amino acid; anticodon complementary to codon; ribosome moves to the next codon or fits two tRNAs; amino acids join by peptide bonds or using ATP.

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From the examiners' report: Only 8.4% got all 5. Don't describe transcription, mRNA doesn't leave the cell, and RNA polymerase doesn't join amino acids. The start codon is not just 'the first codon'.

Question 12

AS Paper 1 · June 2023 · Q04.4 · 2 marks · Hard

Describe the role of tRNA in translation.

Question text: the rate of translation is increased in T cells activated by antigens; describe the role of tRNA in translation, 2 marks.
Show the mark scheme Mark scheme: anticodon on tRNA binds to the complementary codon on mRNA; tRNA brings a specific amino acid to the ribosome.

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From the examiners' report: Many answers were incomplete. Say the anticodon binds to the codon, not just 'complementary base pairing', and that tRNA carries a specific amino acid.

Question 13

AS Paper 2 · June 2017 · Q03.2 · 3 marks

Explain the advantage of having many copies of the amylase gene on a high-starch diet.

Question text: multiple copies of the AMY1 gene are an adaptation to a high-starch diet; use your knowledge of protein synthesis and enzyme action to explain the advantage, 3 marks.
Show the mark scheme Mark scheme: more mRNA or more transcription; more translation or more enzyme (amylase); so the reaction is faster. The idea of 'more' must be stated at least once; 'more starch digested' is insufficient.

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From the examiners' report: No examiners' report for this part. Follow the chain: more copies, more transcription, more translation, more amylase, faster starch hydrolysis.

Using the genetic code and data (3.4.2)

Question 14

AS Paper 1 · June 2025 · Q04.2 · 2 marks · Easy

Use a codon table to give the mRNA sequence and amino acids for a DNA base sequence.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Table 2: mRNA codon table by first, second and third base. Table 3: DNA base sequence G C T C T A C A G with rows to complete for the mRNA base sequence and the amino acid sequence, 2 marks.
Show the mark scheme Mark scheme: mRNA C G A G A U G U C; amino acids Arg, Asp, Val.

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From the examiners' report: Over two thirds got both marks. Swap T for U when you write the mRNA, then read the amino acids from the table in triplets.

Question 15

AS Paper 1 · November 2020 · Q06.3 · 1 mark

Give the amino acid sequence coded by a DNA template strand, using a codon table.

Table 3: mRNA codons for serine, proline, glycine, threonine and alanine. Figure 6: DNA template sequence AGG CGT CCT GGA; question asks for the amino acid sequence, 1 mark.
Show the mark scheme Mark scheme: serine, alanine, glycine, proline, in this order.

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From the examiners' report: No examiners' report for this part. It's a template strand, so write the complementary mRNA codons first (UCC GCA GGA CCU) before you use the table.

Question 16

A level Paper 1 · November 2021 · Q03.3 · 2 marks

Complete a table with the mRNA codon, mutated codon and mutated DNA triplet for an Arg to Gly change.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Table 2: mRNA codon table with a key to the bond formed by each R group. Question text: Arg is replaced by Gly by a single base substitution; the non-mutant DNA triplet is TCC; complete Table 3 with the non-mutant mRNA codon, the mutated codon and the mutated DNA triplet, 2 marks.
Show the mark scheme Mark scheme: AGG; GGG; CCC. Three correct for 2 marks, two correct for 1 mark.

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From the examiners' report: No examiners' report for this paper. Work DNA to mRNA (TCC gives AGG), change one base to get a Gly codon (GGG), then go back to the DNA triplet (CCC).

Question 17

AS Paper 2 · June 2024 · Q04.2 · 3 marks · Hard

Use a DNA–mRNA hybrid experiment to explain why scientists concluded splicing had happened.

Figure 4: an adenovirus gene T is separated into DNA strands A and B; strand A forms a hybrid with mRNA from a host cell, leaving three loops of strand A not paired with the mRNA. Question asks why this supports the conclusion that splicing took place, 3 marks.
Show the mark scheme Mark scheme, max 3: loops of DNA contain introns; DNA in the hybrid contains exons; complementary base pairing or hydrogen bonding between DNA and mRNA; introns removed during splicing; mRNA shorter than the DNA because of splicing.

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From the examiners' report: Students struggled and many wrote everything they knew about splicing. The loops are DNA introns with no matching mRNA; say the DNA and mRNA pair by complementary base pairing.

Question 18

AS Paper 2 · June 2024 · Q04.3 · 2 marks

Describe and explain how the hybrid results would differ with prokaryotic DNA.

Question text: describe and explain how the results of the experiment in Figure 4 (the DNA–mRNA hybrid with loops) would differ if the scientists had used prokaryotic DNA, 2 marks.
Show the mark scheme Mark scheme: no loops of DNA; because there are no introns in prokaryotic DNA.

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From the examiners' report: Almost half scored zero. Prokaryotic DNA is a loop but it is double-stranded; the point is that it has no introns, so no DNA loops form.

Where students lose marks (from AQA examiners' reports and mark schemes)

Each point below is followed by wording that gained marks.

  • The proteome is what a cell can produce: Only 17.9% defined the proteome in 2018, and 13% didn't attempt it. In 2023 many wrote 'all the proteins in a cell' or 'all the proteins a cell codes for' without mentioning the DNA or genome, and 'number of proteins' on its own is never accepted.

    ✔ Gains credit: "(Full) range of proteins that a cell can produce" or "range of proteins coded for by the cell's DNA / genome".

  • A genome belongs to a cell, not a species: Nearly 40% missed the mark for 'genome'. The commonest wrong answers were 'all the genes in a chromosome' or 'all the genes in a species', and some confused genome with genotype. 'All the genetic information' didn't score either.

    ✔ Gains credit: "Complete set of genes in a cell" or "(all) the DNA in a cell / organism".

  • Write each RNA difference as a pair: Students who lost marks comparing mRNA and tRNA didn't state a clear difference, and some thought tRNA is a double-stranded molecule.

    ✔ Gains credit: "tRNA is clover leaf, mRNA is linear"; "tRNA has an amino acid binding site, mRNA does not"; "tRNA has an anticodon, mRNA has codons".

  • Phosphodiester bonds link the RNA nucleotides: Many didn't name phosphodiester bonds, or described bonds forming between bases or between the RNA and the DNA. Some confused phosphodiester bonds with hydrogen bonds, and RNA polymerase 'forming hydrogen bonds' or 'joining complementary bases' is rejected.

    ✔ Gains credit: "RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds, in a condensation reaction."

  • Translation only, so leave transcription out: Only 8.4% got all 5 marks on translation in 2018. Many described transcription anyway, had mRNA leaving the cell, or said RNA polymerase joins amino acids.

    ✔ Gains credit: "mRNA associates with a ribosome; the ribosome moves to the start codon; amino acids join by peptide bonds (using ATP)."

  • tRNA brings a specific amino acid: In 2023 the role of tRNA proved very challenging: answers described complementary base pairing without the anticodon binding to the codon, and said tRNA carries 'an amino acid'. In 2024 few mentioned ATP in forming peptide bonds.

    ✔ Gains credit: "Anticodon on tRNA binds to the complementary codon on mRNA"; "tRNA brings a specific amino acid to the ribosome".

  • No splicing, so the introns stay in: Only 10% scored on why bacteria might not make every human protein. Wrong ideas included bacteria having uracil instead of thymine or lacking amino acids, and many stated 'bacteria cannot splice' without explaining the consequence.

    ✔ Gains credit: "Bacteria cannot splice pre-mRNA, so they cannot remove introns."

  • A loop of DNA isn't a single strand: Almost half scored zero on how the experiment would differ with prokaryotic DNA. Many said prokaryotic DNA is single-stranded, misreading 'a single loop' of DNA.

    ✔ Gains credit: "No loops (of DNA), because there are no introns in prokaryotic DNA."

Download the questions

Download the PDF pack (18 questions, mark schemes at the end)

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Questions, mark schemes and examiners' report extracts © AQA.

Tom Whitburn
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