Cambridge Syllabus Notes

5.1 Enzymes – Biological Catalysts

Enzymes are special proteins that speed up almost every chemical reaction in our bodies. Think of them as super‑fast helpers that make sure life runs smoothly. 🔬

What are enzymes?

Enzymes are proteins that act as biological catalysts. They lower the energy needed for a reaction to happen, so the reaction can occur quickly and efficiently. ⚡

Enzyme action – the lock & key analogy

🔑 Key (substrate) fits into the lock (active site) of the enzyme.
🔧 The enzyme changes shape slightly, helping the substrate react.
🚀 The product is released, and the enzyme is ready for another round.

Key features of enzymes

Made of amino acids (protein).
Highly specific – each enzyme works on one or a few substrates.
Active at a particular temperature and pH.
Can be regulated (turned on/off) by the cell.

Enzyme structure

The active site is a small pocket where the substrate binds. The shape and chemical environment of this pocket determine which substrate fits. 🏗️

Factors affecting enzyme activity

Temperature – too hot or too cold can denature the enzyme.
pH – each enzyme has an optimal pH.
Substrate concentration – more substrate usually means a faster reaction.
Inhibitors – molecules that block the active site.
Activators – molecules that help the enzyme work better.

Enzyme specificity examples

🔬 Amylase breaks down starch into sugars.
🧪 Lactase splits lactose into glucose and galactose.
🛡️ Protease digests proteins into amino acids.

Enzyme kinetics – Michaelis–Menten equation

The rate of an enzyme-catalysed reaction can be described by:

$$v = \frac{V_{\max}[S]}{K_m + [S]}$$

Where v is the reaction rate, V_max is the maximum rate, [S] is substrate concentration, and K_m is the substrate concentration at half V_max. 📈

Parameter	Description
V_max	Maximum reaction rate when all enzyme sites are occupied.
K_m	Substrate concentration at which the reaction rate is half of V_max.
[S]	Current concentration of the substrate.

Exam Tips

• Remember the lock & key model when explaining enzyme specificity.
• Use the Michaelis–Menten equation to calculate reaction rates if given data.
• Be clear about how temperature, pH, and inhibitors affect enzyme activity.
• Practice drawing enzyme structures and labeling active sites.
• Use emojis or simple diagrams (if allowed) to illustrate concepts in your notes.
• Check the exam marking scheme for key terms: catalyst, active site, specificity, denaturation, inhibition.

Describe enzymes as proteins that function as biological catalysts in all metabolic reactions.