AQA AS Level Biology Paper 2, June 2022: Question 1

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

Ignore codes for a

A sequence of DNA (nucleotide) bases that

protein.

codes for a polypeptide;

Accept ‘codes for a

1 functional RNA’ or

01.1 ‘codes for

(AO1) rRNA/tRNAs’ or

‘codes for a sequence

of amino

acids/primary

structure’

1. Pre-mRNA (only) produced in eukaryote (cell);

2. Splicing (only) occurs in eukaryote (cell);

2 max

01.2 3. Introns removed in eukaryote (cell)

(2 x AO1)

OR

Introns not present in prokaryote (cell);

1. PNA is complementary to DNA

OR

PNA forms base pairs with DNA;

2. Preventing/reducing RNA polymerase 2

01.3 activity/binding

(2 x AO2)

OR

Prevents RNA nucleotides binding

OR

Reducing/stopping transcription;

1. Releases/provides energy; 1. Reject ‘produce

energy’

2. (So) peptide bonds form between amino acids

01.4

OR (2 x AO1)

(So) amino acid joins to tRNA;

How to answer it

Genes, Transcription, and Translation Study Guide

What this question tests:
This question pack assesses your foundational knowledge of molecular genetics (AS Level Biology). It tests your understanding of the definition of a gene, structural differences in transcription between eukaryotes and prokaryotes, application of complementary base pairing in experimental contexts (PNA binding), and the specific energetic role of ATP during protein translation.

Question 01.1

Defining a Gene

What is a gene? [1 mark]

✅ Correct Answer

A sequence of DNA (nucleotide) bases that codes for a polypeptide (or functional RNA).

💡 Key Knowledge

Must mention DNA or bases . Vague answers like "a piece of DNA" are insufficient.
Acceptable alternatives: codes for a functional RNA, rRNA, tRNA, or a sequence of amino acids / primary structure.

❌ Common Errors

Stating that a gene "codes for a protein" without specifying a polypeptide or functional product (examiners prefer precision at A Level).
Forgetting to reference bases or nucleotide sequence.

Mark scheme note: 1 mark awarded for AO1 recall.

Question 01.2

Eukaryotic vs. Prokaryotic Transcription

Describe how the production of messenger RNA (mRNA) in a eukaryote cell is different from the production of mRNA in a prokaryote cell. [2 marks]

✅ Correct Answer (Any 2 points)

Pre-mRNA is only produced in eukaryote cells.
Splicing only occurs in eukaryote cells (introns are removed).
Introns are not present in prokaryotic DNA.

🧠 Exam Technique

This is a "contrast" question. To secure both marks, make sure your answer clearly highlights what happens in eukaryotes versus prokaryotes, or specifically details the processing steps unique to eukaryotes (pre-mRNA and splicing).

❌ Common Errors

Confusing transcription with translation locations.
Failing to mention introns or splicing, relying instead on vague descriptions of "processing".

Mark scheme note: 2 marks max (2 × AO1). Points must clearly distinguish between the two cell types.

Question 01.3

Inhibiting Transcription with PNA

Suggest how PNA affected the transcription of the section of DNA. [2 marks]

✅ Correct Answer (Any 2 points)

PNA is complementary to DNA / forms base pairs with DNA.
Prevents or reduces RNA polymerase activity / binding.
Prevents free RNA nucleotides from binding / stops transcription.

💡 Key Knowledge

Because PNA is single-stranded and artificial, it relies on standard complementary base pairing rules (A-T, C-G) to bind to the template or coding strand of DNA, physically blocking transcription machinery.

🧠 Exam Technique

This is an AO2 (Application) question. Do not just restate the stem; explain the mechanism. Link the binding of PNA (Point 1) directly to the obstruction of RNA polymerase or nucleotide addition (Point 2).

Mark scheme note: 2 marks (2 × AO2).

Question 01.4

The Role of ATP in Translation

Describe the role of ATP in the process of translation in protein synthesis. [2 marks]

✅ Correct Answer (Any 2 points)

Releases / provides energy.
Enables peptide bonds to form between amino acids.
Enables amino acids to join to tRNA molecules.

❌ Common Errors & Examiner Traps

CRITICAL TRAP: Never write that ATP is "produced" or "made" in this context. Examiners strictly reject "produce energy" due to the law of conservation of energy. Always use "releases" or "provides" energy.
Confusing the role of ATP in translation with its role in transcription or active transport.

Mark scheme note: 2 marks (2 × AO1). Reject 'produce energy'.

Topics

Biology · 3.1 Biological molecules · 3.4 Genetic information, variation and relationships between organisms