Chapter 3 : Enzymes – Class 11 Federal Board Biology Notes (Free PDF)
Chapter 2 Enzymes Class 11 Notes are designed for quick revision before exams, covering essential topics like enzyme structure, function, types, mechanism of action, factors affecting activity, inhibition, classification, and applications. These notes simplify complex concepts with clear explanations, key points, and concise summaries, making it easier for students to understand and retain important information effectively.
Enzymes
- Metabolism = Sum of all chemical rxns in a cell.
- Enzymes = Biological catalysts → ↑ rxn speed w/o consumption.
Properties:
✅ ↑ Speed of chemical rxns.
✅ Small qty required.
✅ pH & Temp sensitive.
✅ Specificity: Highly or slightly specific.
✅ Work in vivo & vitro.
✅ Some need cofactors for activity.
✅ ↓ Activation energy.
✅ No effect on equilibrium.
- Payen & Persoz (19th century) → Discovered diastase, an enzyme digesting starch.
Enzyme Structure
- Globular proteins (except ribozymes).
- Ribozymes = RNA-based enzymes (e.g., peptidyl transferase).
- Active Site = 3D cavity where rxn occurs.
- Binding site = Holds substrate.
- Catalytic site = Converts substrate → product.
Cofactors:
- Holoenzyme = Enzyme + cofactor (active).
- Apoenzyme = Enzyme w/o cofactor (inactive).
- Pepsinogen → Pepsin (Activated in HCl).
Types of Cofactors
🔹 Inorganic (Activators) → Fe²⁺, Mg²⁺, Cu²⁺, Zn²⁺ (Detach after rxn).
🔹 Organic:
- Coenzymes (Vitamin derivatives) → ATP, NAD⁺, FAD⁺.
- Prosthetic groups (Permanently attached) → Heme in cytochromes.
Mechanism of Enzyme Action
- E + S → ES → EP → E + P
- Enzyme alters pH, charge, bond stress → Easier rxn.
Models of Action
- Lock & Key (Fischer, 1894) → Fixed shape active site, highly specific.
- Induced Fit (Koshland, 1959) → Flexible active site, molds to substrate.
Activation Energy (Ea)
- Enzymes ↓ Ea, making rxns possible w/o excessive heat.
- Rxn Pathway:
A + E → AE Complex + B → AB + E
Factors Affecting Enzymes
Temp:
- Optimum: Max activity (~37°C humans, ~70°C bacteria).
- Too high → Denaturation.
- Too low → Inactive but reversible.
pH:
- Optimum pH varies (e.g., Pepsin = 2, Trypsin = 8).
- Extreme pH → Denaturation.
[Enzyme] ↑ → Rxn rate ↑ (until substrate saturation).
[Substrate] ↑ → Rxn rate ↑, but plateaus at Vmax.
Enzyme Inhibition
❌ Competitive (Reversible)
- Inhibitor competes for active site.
- Example: Malonate inhibits succinate dehydrogenase.
❌ Non-Competitive (Reversible or Irreversible)
- Binds allosteric site, alters active site shape.
- Example: Cyanide inhibits cytochrome oxidase.
🔄 Feedback Inhibition
- End product inhibits 1st enzyme in pathway.
- Example: Threonine inhibits 1st enzyme in its synthesis pathway.
Enzyme Classification (IUB 1961)
1️⃣ Oxidoreductases (Redox rxns) → Cytochrome oxidase.
2️⃣ Transferases (Transfer groups) → Hexokinase.
3️⃣ Hydrolases (Hydrolysis) → Pepsin, trypsin.
4️⃣ Lyases (Break bonds w/o H₂O) → Histidine decarboxylase.
5️⃣ Isomerases (Rearrange molecules) → Phosphohexose isomerase.
6️⃣ Ligases (Join molecules using ATP) → DNA ligase.
Enzyme Uses
🏭 Industry:
- Food → Amylase (syrups), Protease (meat tenderizing).
- Detergents → Lipase & Protease (stain removal).
- Paper/Leather → Ligninase (bleaching), Protease (hide processing).
🏥 Medicine:
- Diagnosis → ALT, AST (Liver), Troponin (Heart).
- Treatment → Streptokinase (Clot dissolving), Asparaginase (Cancer).
🧬 Genetic Engineering:
- DNA cutting → Restriction enzymes.
- DNA joining → Ligases.
- DNA copying → Polymerases (PCR).
Next topic
Exercise | Chapter 3 : Enzymes | Class 11 Biology
(click any Question to view Answer)
1. Enzyme Structure & Function
- What are ribozymes?
- What is the structure of an enzyme?
- Explain the enzyme pepsin which does not require a cofactor.
- What is a prosthetic group? Give an example.
- What is the role of the active site in an enzyme?
2. Mechanism of Enzyme Action
- What is the mechanism of enzyme action?
- Describe the Induced Fit Model vs. Lock and Key Model.
- How does an enzyme catalyze specific reactions?
3. Factors Affecting Enzyme Activity
- What is the role of free energy of activation in a chemical reaction?
- List the external conditions that affect the rate of enzyme reaction.
- Compare the optimum temperatures of enzymes of humans and thermophilic bacteria.
- Describe the range of pH at which human enzymes function.
4. Enzyme Inhibition & Regulation
- What are enzyme inhibitors? Name the molecules that act as enzyme inhibitors.
- What is the importance of competitive enzyme inhibitors?
- Describe cyanides as irreversible non-competitive inhibitors.
- Describe ions of heavy metals as irreversible non-competitive inhibitors.
- Explain Feedback Inhibition with an example.
5. Enzyme Classification
- Classification of enzymes by reaction type (IUB 1961).
- Classification of enzymes by substrate type.
6. Enzyme Properties & Applications
- Properties of enzymes.
- Effect of temperature on enzyme action.
- Effect of enzyme concentration on reaction rate.
- Effect of substrate concentration on reaction rate.
- Enzymatic inhibition, types, and significance.
