AQA A-Level Chemistry Paper 3, June 2025: Question 34

1 mark · Easy difficulty · Multiple Choice

Identify the correct statement about enzymes from the given options.

Practise this question

Question

Multiple choice question asking 'Which statement about enzymes is correct?' with four options: A 'Enzymes are a type of nucleotide', B 'Enzymes are polymers', C 'Enzymes are not affected by changes of pH', and D 'Enzymes act as catalysts by increasing activation energy'.
Question text

34 Which statement about enzymes is correct?

[1 mark]

A Enzymes are a type of nucleotide.

B Enzymes are polymers.

C Enzymes are not affected by changes of pH.

D Enzymes act as catalysts by increasing activation energy.

Mark scheme

Show the mark scheme Mark scheme indicating the correct answer for question 34 is option B, 'Enzymes are polymers', worth 1 mark (AO1).

34 B 1 (AO1) Enzymes are polymers.

How to answer it

Structure and Properties of Enzymes

📋 What this question tests

Fundamental recall and understanding of biological molecules in organic chemistry (Topic 3.3.13 Amino acids, proteins and DNA). Specifically, knowledge of the macromolecular nature of enzymes (globular proteins made of amino acid polymers), how enzymes function as biological catalysts by lowering activation energy, and their sensitivity to pH and temperature changes.

Question 34 • Multiple Choice • 1 Mark

Identifying the Correct Statement About Enzymes

AQA Chemistry A-Level • Paper 2 Organic and Physical Chemistry

✅ Correct Answer

B: Enzymes are polymers.

Mark Scheme Breakdown:
• B (1 mark, AO1 recall)

Enzymes are globular proteins, which are condensation polymers formed from monomer units of 2-amino acids joined together by peptide (amide) bonds.

💡 Key Knowledge

  • Protein Structure: Enzymes are polypeptide chains folded into unique three-dimensional shapes held by hydrogen bonds, ionic interactions, and disulfide bridges.
  • Catalytic Action: Like all chemical catalysts, enzymes provide an alternative reaction pathway with a lower activation energy (Ea).
  • Sensitivity: Changes in pH or temperature alter ionic charges and hydrogen bonding, causing denaturation (loss of tertiary structure).
  • Nucleotides vs Proteins: Nucleotides are the monomers that make up DNA/RNA (polynucleotides), not enzymes.

🧠 Exam Technique: Systematic Option Elimination

  • Option A: Incorrect — Enzymes are proteins made of amino acids, not nucleotides. (DNA is a polymer of nucleotides).
  • Option B: Correct — Polypeptides are condensation polymers made from amino acid monomers.
  • Option C: Incorrect — Notice the negative word "not". Enzymes are very sensitive to pH; deviations from optimum pH disrupt ionic interactions and denature the active site.
  • Option D: Incorrect — Catalysts lower activation energy, never increase it.

❌ Common Errors & Misconceptions

  • Forgetting that proteins are polymers: Students often think of synthetic plastics (like polyalkenes, nylon, or Terylene) when they hear the word "polymer", forgetting that proteins, starch, and DNA are naturally occurring condensation polymers.
  • Misreading Option D: Skimming too quickly and seeing the words "catalysts" and "activation energy" without spotting the word "increasing" instead of "decreasing".
  • Confusing RNA/DNA with enzymes: Conflating genetic polymers (polynucleotides) with catalytic proteins (polypeptides).

Topics

Organic Chemistry · 3.3.13 Amino Acids, Proteins and DNA

Question and mark scheme from the AQA A-Level Chemistry examination, Paper 3, June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.