Edexcel iGCSE Biology-2.10 role of enzymes- Study Notes- New Syllabus

Enzymes – Biological Catalysts

📝 Introduction

• In living organisms, chemical reactions = metabolic reactions (e.g., respiration, photosynthesis, digestion).
• These reactions are usually too slow at normal body temperatures.
• Cells use enzymes (special proteins) to speed them up safely.

Enzymes = biological catalysts.

🔑 Key Features of Enzymes

• Proteins (made of amino acids).
• Catalysts → speed up reactions without being used up.
• Specific → one enzyme works on one substrate (“lock and key” idea).
• Work best at an optimum temperature + pH.

🧪 Role in Metabolic Reactions

1. Digestion (breaking molecules)

• Amylase: starch → maltose
• Protease: protein → amino acids
• Lipase: fat → fatty acids + glycerol

These reactions would be too slow without enzymes.

2. Respiration & Energy Release

• Enzymes control each step of breaking down glucose in respiration.
• Release of ATP (energy) is fast enough to support life.

3. Photosynthesis

• Controlled by enzymes (e.g., rubisco) in chloroplasts.
• Helps plants convert CO₂ + H₂O → glucose + O₂.

4. DNA & Protein Synthesis

• Enzymes control copying DNA before cell division.
• Also join amino acids together to build proteins.

🔑 Why Enzymes Are Essential

Without enzymes, most metabolic reactions would be far too slow to support life.

Enzymes allow reactions to happen:

• Fast enough
• At normal body temperatures (not extreme heat like in labs)

They make metabolism efficient and controlled.

📊 Summary Table – Enzyme Role in Metabolism

⚡ Quick Recap 
Enzymes = biological catalysts (proteins).
Speed up reactions without being used up.
Specific to substrates (“lock & key”).
Roles: digestion, respiration, photosynthesis, DNA/protein synthesis.
Without enzymes → reactions too slow → life impossible.