Unit Overview

Enzymes

CIE A-Level Biology· 5 min read 📊 n/a

1. Unit at a Glance

Enzymes are critical to life, as they allow metabolic reactions to proceed at the rates required for cell function at normal physiological temperatures. This unit builds sequentially: starting from core properties and mechanism of action, moving to factors that change enzyme activity, how inhibitors regulate function, and ending with real-world industrial applications of immobilised enzymes.

This unit is split into 4 core sub-topics:

Enzyme properties and mode of action

Covers enzyme structure as globular catalysts, activation energy, and the induced fit and lock-and-key models of substrate binding.

★★⏱ 10 min

Factors affecting enzyme activity

Explores how temperature, pH, substrate concentration and enzyme concentration affect reaction rate and enzyme tertiary structure.

★★⏱ 12 min

Enzyme inhibitors

Compares competitive and non-competitive inhibitors, including their effects on reaction kinetics and practical biological examples.

★★★⏱ 10 min

Immobilised enzymes

Describes common methods of immobilisation and the advantages and industrial applications of immobilised enzymes.

★★★⏱ 8 min

2. Common Pitfalls

Wrong move:

Confusing competitive and non-competitive inhibitors in terms of their effect on $V_{ma x}$ and $K_{m}$ .

Why:

Students often mix up binding sites and resulting kinetic changes, leading to incorrect exam answers.

Correct move:

Competitive inhibitors bind the active site, so they do not change $V_{ma x}$ but increase $K_{m}$ ; non-competitive bind allosteric sites, lowering $V_{ma x}$ with no change to $K_{m}$ .

Wrong move:

Claiming enzymes are 'used up' in the reactions they catalyse.

Why:

This common misconception confuses enzymes with reactants in metabolic pathways.

Correct move:

Enzymes are biological catalysts, so they remain unchanged at the end of a reaction and can be reused multiple times.

Wrong move:

Drawing pH/temperature enzyme activity curves starting from 0 rate and rising after the optimum point.

Why:

Students often forget that denaturation is irreversible after the optimum is passed.

Correct move:

For both temperature and pH, reaction rate falls to zero after the optimum as the enzyme's tertiary structure is permanently denatured.

3. Quick Reference Cheatsheet

Key Concept	Core Summary
Activation Energy	Minimum energy required for a reaction to proceed; enzymes lower this to increase reaction rate
Competitive Inhibitor	Binds enzyme active site, increases $K_{m}$ , no change to maximum reaction rate $V_{ma x}$
Non-competitive Inhibitor	Binds allosteric (non-active) site, decreases $V_{ma x}$ , no change to $K_{m}$
Effect of Temperature	Rate increases until optimum temperature; denaturation after optimum causes rate to drop to zero
Core Advantage of Immobilised Enzymes	Easily separated from products, can be reused, and more stable to changes in pH and temperature

What's Next

Begin your study of this unit with the first sub-topic to build your foundational understanding of enzyme structure and catalytic mechanism. Once you complete all sub-topics in this unit on enzymes, you will move on to the next unit covering cell membranes and transport, another core topic for understanding cellular function.