BIO101 – Topic 9: Enzymes and Metabolism
Course Code: BIO 101
Course Name: General Biology
9.1 Definition and Nature of Enzymes
Enzymes are biological catalysts — proteins that speed up chemical reactions in living organisms
without being consumed in the process. They lower the activation energy required for reactions,
allowing life processes to occur efficiently at body temperature.
Examples:
• Amylase – breaks down starch to maltose
• Lipase – breaks down fats into fatty acids and glycerol
• Catalase – breaks down hydrogen peroxide into water and oxygen.
9.2 Properties of Enzymes
1. Enzymes are proteins in nature.
2. They are specific in their action.
3. They work best under optimum temperature and pH.
4. They are not used up in the reactions they catalyze.
5. They speed up both forward and reverse reactions.
6. They are denatured by extreme temperature or pH changes.
9.3 Factors Affecting Enzyme Activity
• Temperature: Enzyme activity increases with temperature up to an optimum point (~37°C). Beyond
this, enzymes are denatured.
• pH: Each enzyme has an optimum pH (e.g., pepsin works best in acidic medium).
• Substrate Concentration: Activity increases with substrate until saturation.
• Enzyme Concentration: More enzymes speed up reactions if substrate is available.
• Presence of Inhibitors: Some substances slow or stop enzyme action.
9.4 Enzyme Inhibition
Enzyme inhibitors interfere with enzyme activity.
Types:
• Competitive inhibitors: Compete with substrate for the active site (e.g., malonic acid inhibits
succinate dehydrogenase).
• Non-competitive inhibitors: Bind elsewhere on the enzyme, changing its shape so the substrate
cannot bind.
9.5 Metabolism: Anabolism and Catabolism
Course Code: BIO 101
Course Name: General Biology
9.1 Definition and Nature of Enzymes
Enzymes are biological catalysts — proteins that speed up chemical reactions in living organisms
without being consumed in the process. They lower the activation energy required for reactions,
allowing life processes to occur efficiently at body temperature.
Examples:
• Amylase – breaks down starch to maltose
• Lipase – breaks down fats into fatty acids and glycerol
• Catalase – breaks down hydrogen peroxide into water and oxygen.
9.2 Properties of Enzymes
1. Enzymes are proteins in nature.
2. They are specific in their action.
3. They work best under optimum temperature and pH.
4. They are not used up in the reactions they catalyze.
5. They speed up both forward and reverse reactions.
6. They are denatured by extreme temperature or pH changes.
9.3 Factors Affecting Enzyme Activity
• Temperature: Enzyme activity increases with temperature up to an optimum point (~37°C). Beyond
this, enzymes are denatured.
• pH: Each enzyme has an optimum pH (e.g., pepsin works best in acidic medium).
• Substrate Concentration: Activity increases with substrate until saturation.
• Enzyme Concentration: More enzymes speed up reactions if substrate is available.
• Presence of Inhibitors: Some substances slow or stop enzyme action.
9.4 Enzyme Inhibition
Enzyme inhibitors interfere with enzyme activity.
Types:
• Competitive inhibitors: Compete with substrate for the active site (e.g., malonic acid inhibits
succinate dehydrogenase).
• Non-competitive inhibitors: Bind elsewhere on the enzyme, changing its shape so the substrate
cannot bind.
9.5 Metabolism: Anabolism and Catabolism
