AQA AS Level Biology Paper 1, June 2023: Question 1

Mark scheme

Show the mark scheme

Question Marking Guidance Mark Comments

1. Sequence/order of amino acids; 2

01.1 (2 x

2. (Joined by) peptide bonds; AO1)

AAAccept ‘3 bases’ for

1. (Universal) The same codon/triplet always codes

triplet

for the same amino acid;

2. (Non-overlapping) Each base is only part of one 2. Accept

triplet/codon ‘base/triplets/codons

only read once’

01.2 (3 x

OR

AO1)

(Adjacent) codons/triplets do not overlap;

3. (Degenerate) More than one codon/triplet codes

for each amino acid;

How to answer it

Proteins and the Genetic Code Study Guide

What this question tests

This assessment tests your foundational recall and precise definitions (AO1) regarding protein structure and the key features of the genetic code. You must use exact biological terminology without substituting keywords like "bases", "codons", and "amino acids".

Question 01.1 — [2 marks]

Describe the primary structure of all proteins.

✅ Correct Answer

1. Sequence / order of amino acids.
2. (Joined by) peptide bonds.

💡 Key Knowledge

Primary structure dictates the folding and overall 3D shape of a protein.
Peptide bonds are formed via condensation reactions between the amine group of one amino acid and the carboxyl group of another.

🧠 Exam Technique

Keep your sentences concise. Both marking points are standalone required keywords. Do not waste time describing secondary or tertiary structures like alpha helices or hydrogen bonds.

❌ Common Errors

Stating "amino acids joined by glycosidic bonds" (confusing proteins with carbohydrates).
Vague answers like "the chain of proteins" instead of specifying amino acids.

Mark Scheme Breakdown: 1 mark for sequence/order of amino acids + 1 mark for peptide bonds. (2 x AO1)

Question 01.2 — [3 marks]

Define universal, non-overlapping, and degenerate with respect to the genetic code.

✅ Correct Answers

Universal: The same codon / triplet always codes for the same amino acid (in all organisms).
Non-overlapping: Each base is only part of one triplet/codon (or adjacent codons/triplets do not overlap / base-triplets are only read once).
Degenerate: More than one codon / triplet codes for a single amino acid.

💡 Key Knowledge

Make sure you do not confuse these three terms. Examiners frequently see students mix up "degenerate" and "universal". Remember: Universal = shared across species; Degenerate = multiple options for one amino acid.

❌ Common Errors

For degenerate: Saying "more than one amino acid codes for a codon" (this is backward and biologically incorrect).
For non-overlapping: Stating that "amino acids don't overlap" instead of referencing bases/codons.

Mark Scheme Breakdown: 1 mark per correct definition. Total 3 marks (3 x AO1).

Topics

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