IGCSE Biology Topic 5: Enzymes
Introduction to Enzymes
- Enzymes are biological catalysts.
- Catalysts increase the rate of chemical reactions without being changed by the reaction.
- Metabolic reactions are constantly occurring in organisms to maintain life.
- Enzymes are proteins that speed up metabolic reactions.
Function of Enzymes
- Enzymes maintain reaction rates necessary for life.
- Example: Digestive enzymes help break down food molecules for energy and nutrients.
- Substrate: The substance on which the enzyme acts.
- Product: The molecules produced after the reaction.
- Active Site: The specific shape on the enzyme where the substrate binds.
- Enzyme-Substrate Complex: Formed temporarily when the enzyme binds with the substrate.
Enzyme Specificity
- Enzymes are specific to their substrate molecules.
- The active site and substrate shapes are complementary (lock and key mechanism).
- Enzymes cannot act on substances if the shapes do not match.
Factors Affecting Enzyme Activity
Temperature
- Reaction rate increases with temperature due to higher kinetic energy and more frequent collisions.
- Each enzyme has an optimum temperature where it functions best.
- High temperatures can denature enzymes, changing the active site's shape and stopping functionality.
- Low temperatures reduce enzyme activity due to less energy and fewer successful collisions.
- Typical human enzyme optimum temperature: ~37°C.
- Enzymes start denaturing above 50°C.
pH
- Enzymes have an optimum pH where they work best.
- Deviations from the optimum pH can break enzyme bonds, change the active site shape, and denature enzymes.
- Different enzymes work best at different pH levels.
- Pepsin: Optimum pH around 2 (stomach enzyme).
- Amylase: Optimum pH around 7 (salivary enzyme).
- Enzymes are ineffective if the pH is too far from their optimum.
Conclusion
- Enzymes are crucial for speeding up metabolic reactions in organisms.
- Temperature and pH are key factors influencing enzyme activity.
- Understanding enzyme specificity and environmental effects is vital for grasping their biological roles.
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