AQA AS Level Biology Paper 1, June 2022: Question 5
9 marks · Medium difficulty · Short Answer
Describe protein primary structure formation, compare lock-and-key and induced-fit enzyme models, explain enzyme action at lower temperatures, calculate time taken for maltase hydrolysis, and identify the independent variable for an enzyme reaction curve.
Practise this questionQuestion
Question text
05.1 Describe how monomers join to form the primary structure of a protein.
[3 marks]
05.2 Many proteins are enzymes.
In 1894, a scientist suggested the lock and key model of enzyme action.
Figure 5 shows the lock and key model.
Figure 5
Describe one similarity and one difference between the induced-fit model of enzyme
action and the lock and key model of enzyme action.
[2 marks]
Similarity
Difference
05.3 State how enzymes help reactions to proceed quickly at lower temperatures.
Do not write about active sites in your answer.
[1 mark]
05.4 The enzyme maltase catalyses the hydrolysis of maltose to glucose.
A scientist investigated maltase activity in two different maltose solutions, G and H.
For each solution, he measured:
• the total number of glucose molecules produced by complete hydrolysis of the
maltose
• the time taken for the complete hydrolysis of the maltose.
Table 3 shows his results.
Table 3
Total number of glucose Time taken for complete
Solution
molecules produced hydrolysis of maltose / s
G 4 × 107 20
H 6 × 108
Complete Table 3 by calculating the time taken for the complete hydrolysis of the
maltose in solution H. Assume the rate of maltase activity is the same in solution G
and in solution H.
Show your working.
[2 marks]
05.5 Figure 6 shows the scientist’s results for solution G. Curve I shows the results of a
similar investigation in which he changed one independent variable.
Figure 6
Tick ( ) one box next to the statement that describes the independent variable that
the scientist changed to give the results shown by curve I in Figure 6.
[1 mark]
Addition of a competitive inhibitor
Increased maltase concentration
Increased maltose concentration
Reduced temperature
Mark scheme
Show the mark scheme
Question Marking Guidance Mark Comments
05.1 1. Condensation reaction between amino acids; 1. Accept descriptions
of condensation
2. (Forming) peptide bonds; 3
reaction: eg loss of
(3 x AO1)
3. Creating (specific) sequence/order of amino water
acids;
05.2 (Similarity)
1. Substrate fits/binds to active site
OR
Enzyme-substrate complex (formed);
(Difference)
(2 x AO2)
2. Active site changes shape, but does not 2. Reject ‘substrate
change in lock and key changes shape’
OR 2. Accept ‘flexible’ for
changes shape and
‘rigid’ for does not
(Initially) active site not complementary to change
substrate with induced-fit, but is
complementary in lock and key;
05.3 Lower/reduce activation energy (needed to start 1
a reaction); (AO1)
05.4 Correct answer for 2 marks = 300;;
Accept for 1 mark,
2 000 000 or 2 × 10 (correct calculation of
maltase rate per second)
OR (2 x AO2)
6 × 108 ÷ 4 × 107
OR
× 15 (correct division but not multiplied by 20) – LOGY – – JUNE 2022
05.5 Increased maltase concentration;
(AO3)
How to answer it
Proteins, Enzymes, and Reaction Rates Study Guide
What this question tests
This sequence of questions assesses your knowledge of protein primary structure formation (condensation reactions and peptide bonds), enzyme-substrate interaction models (lock and key vs. induced fit), activation energy principles, quantitative rate calculations involving proportions, and the interpretation of enzyme kinetics graphs.
Protein Primary Structure Formation
✅ Correct Answer
- Condensation reaction between amino acids
- Formation of peptide bonds
- Creation of a specific sequence / order of amino acids
💡 Key Knowledge
Amino acids join via peptide bonds. A molecule of water is eliminated during each condensation reaction between the amine group (-NH₂) and carboxyl group (-COOH) of adjacent amino acids.
🧠 Exam Technique
Be precise with biological terminology. Examiners specifically look for the terms condensation reaction, peptide bond, and sequence. Mentioning the loss of water is also universally accepted.
❌ Common Errors
Students often lose marks by vaguely stating "amino acids bond together" without specifying the type of bond or reaction. Avoid saying "glycosidic bonds" (which are for carbohydrates).
Lock and Key vs. Induced-Fit Models
✅ Correct Answer
Similarity: Substrate fits/binds to the active site OR an enzyme-substrate complex is formed.
Difference: In the induced-fit model, the active site changes shape as the substrate binds, whereas in the lock-and-key model, the active site is already fully complementary and rigid.
💡 Key Knowledge
The lock-and-key model assumes a rigid active site perfectly matched to the substrate. The modern induced-fit model explains that the enzyme's active site molds and conforms around the substrate as it binds.
🧠 Exam Technique
Ensure you clearly split your answer into a labeled similarity and difference. Do not state that "the substrate changes shape"—the active site of the enzyme changes shape.
Enzymes and Activation Energy
✅ Correct Answer
Lower / reduce activation energy (needed to start a reaction).
❌ Common Errors
The question explicitly states: "Do not write about active sites in your answer." Mentioning active sites will cost you the mark instantly, even if you correctly reference activation energy.
Enzyme Calculation: Rate and Proportions
📐 Step-by-Step Calculation
- Find the rate for Solution G:
Rate = 4 × 10⁷ glucose molecules ÷ 20 s = 2,000,000 (or 2 × 10⁶ ) glucose molecules per second. - Apply the same rate to Solution H:
Time = Total glucose ÷ Rate
Time = 6 × 10⁸ ÷ (2 × 10⁶) - Final Answer:
300 seconds.
🧠 Exam Technique & Marking
This is a 2-mark question. Writing the correct final answer 300 secures both marks. If your final calculation is wrong, showing intermediate working (such as calculating the correct rate per second for solution G, or showing 6 × 10⁸ ÷ 4 × 10⁷ × 20 ) can earn you 1 mark.
Interpreting Enzyme Kinetics Graphs
✅ Correct Answer
Tick: Increased maltase concentration
💡 Key Knowledge
Increasing enzyme concentration increases the rate of reaction (steeper initial gradient on the curve) while producing the exact same total final yield of product, provided the substrate concentration is kept constant.
❌ Common Errors
Students often confuse enzyme concentration changes with substrate concentration changes. Changing substrate concentration would alter the plateau height (maximum yield of glucose), whereas changing enzyme concentration reaches the same final yield faster.
Topics
Biology · Practical skills · 3.1 Biological molecules · Data analysis
Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.