Edexcel A Level (IAL) Biology -2.7 Enzymes: Roles & Modes of Action- Study Notes- New Syllabus
Edexcel A Level (IAL) Biology -2.7 Enzymes: Roles & Modes of Action- Study Notes- New syllabus
Edexcel A Level (IAL) Biology -2.7 Enzymes: Roles & Modes of Action- Study Notes -Edexcel A level Biology – per latest Syllabus.
Key Concepts:
- 2.7 (i) understand the mechanism of action and the specificity of enzymes in terms of their three-dimensional structure
(ii) understand that enzymes are biological catalysts that reduce activation energy
(iii) know that there are intracellular enzymes catalysing reactions inside cells and extracellular enzymes catalysing reactions outside cells
Enzymes – Biological Catalysts
🌱 Introduction
Enzymes are biological catalysts that speed up chemical reactions without being consumed.
They are usually globular proteins with a specific three-dimensional structure.
Their function depends on their shape, which allows them to recognize specific substrates.
(i) Mechanism of Action & Specificity
1. Mechanism of Action
- Substrate binds to the active site of the enzyme.
- Enzyme-substrate complex forms → lowers activation energy needed for the reaction.
- Reaction occurs → product is released.
- Enzyme remains unchanged and can catalyze another reaction.
2. Specificity
- Enzymes are highly specific — they only catalyze certain reactions.
- Active site shape matches the substrate like a lock and key or via induced fit.
- The 3D structure of enzymes is essential for this specificity.
Example:
Amylase only breaks down starch into maltose.
It cannot act on proteins or fats because the active site shape doesn’t fit those molecules.
(ii) Enzymes Reduce Activation Energy
Activation energy (Ea): minimum energy required for a reaction to occur.
Enzymes stabilize the transition state, reducing Ea.
Reaction happens faster at lower energy cost.
(iii) Intracellular & Extracellular Enzymes
| Type | Location | Function | Examples |
|---|---|---|---|
| Intracellular | Inside cells | Catalyze reactions within the cell | Catalase (breaks H₂O₂), Dehydrogenase |
| Extracellular | Secreted outside cells | Catalyze reactions outside the cell | Amylase (saliva), Lipase (pancreas) |
⚡ Summary
- Enzymes = biological catalysts
- Mechanism: substrate binds → enzyme-substrate complex → product → enzyme unchanged
- Specificity: determined by 3D active site shape
- Function: lowers activation energy → faster reaction
- Location: intracellular (inside cells) vs extracellular (outside cells)
🧠 Quick Recap
Catalyst: speeds up reaction, not consumed
Activation energy ↓ → faster reaction
Active site: shape determines specificity (lock & key / induced fit)
Intracellular: metabolism inside cells (e.g., catalase)
Extracellular: digestion outside cells (e.g., amylase, lipase)