Unit 5: Enzymes

February 20, 2026

Semester 2
BP203T

Introduction to Enzymes

Unit 5 covers enzymes – the biological catalysts that drive all metabolic reactions. You will learn their classification, how they speed up reactions (Mechanism of Action), and critically, their kinetics using the Michaelis-Menten equation and Lineweaver-Burk plot. This unit is highly important for Pharmacology as many drugs work by inhibiting specific enzymes.

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Syllabus & Topics

  • 1Introduction to Enzymes: Definition, characteristics, and properties.
  • 2Nomenclature of Enzymes: Common names and systematic IUPAC names.
  • 3IUB Classification of Enzymes: 6 major classes (Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases, Ligases) with examples.
  • 4Enzyme Kinetics: Michaelis-Menten Equation (derivation concept), Km and Vmax.
  • 5Lineweaver-Burk (Double Reciprocal) Plot: How to determine Km and Vmax.
  • 6Enzyme Inhibitors: Competitive, Non-competitive, and Irreversible inhibitors with examples.
  • 7Effect of inhibitors on Km and Vmax (from LB plots).
  • 8Regulation of Enzymes: Enzyme induction and repression.
  • 9Allosteric Enzyme Regulation: Allosteric activators and inhibitors.
  • 10Therapeutic Applications of Enzymes: e.g., Streptokinase (thrombolytic), Asparaginase (anticancer).
  • 11Diagnostic Applications of Enzymes: Isoenzymes – LDH (Myocardial Infarction), CK-MB, ALT/AST (Liver damage).
  • 12Coenzymes: Structure and biochemical functions of Vitamin-derived coenzymes (NAD+, FAD, CoA).

Learning Objectives

Classify Enzymes: Give one example enzyme for each of the 6 IUB classes.
Explain Km: Define Km and state what a high Km value means about enzyme-substrate affinity.
Draw LB Plot: Draw a Lineweaver-Burk plot and show where Km and Vmax are read.
Distinguish Inhibition Types: Draw LB plots for Competitive vs Non-Competitive inhibition.
Diagnostic Use: Explain why serum LDH and CK-MB are measured after a suspected heart attack.

Frequently Asked Questions (FAQs)

Q1. What is the Michaelis–Menten Constant (Km)?

The Michaelis–Menten constant (Km) is the substrate concentration at which the reaction velocity is half of Vmax. It indicates the affinity of an enzyme for its substrate.

  • Low Km → High affinity

  • High Km → Low affinity

Q2. What is the difference between Competitive and Non-Competitive inhibition?

  1. Competitive inhibition: The inhibitor binds to the active site of the enzyme.

    • Km increases

    • Vmax remains unchanged

  2. Non-competitive inhibition: The inhibitor binds to a site other than the active site.

    • Vmax decreases

    • Km remains unchanged

Q3. What are Isoenzymes and why are they clinically important?

Isoenzymes (isozymes) are different forms of the same enzyme that catalyze the same reaction but differ in structure and tissue distribution.
For example, CK-MB (Creatine Kinase-MB) is specific to cardiac muscle, and its elevated level in blood is used to help diagnose a myocardial infarction (heart attack).

Q4. What are Allosteric Enzymes?

Allosteric enzymes are regulatory enzymes that possess an allosteric site in addition to the active site. Binding of an activator or inhibitor at this site changes the enzyme’s conformation and activity.

Q5. What is the role of NAD⁺ and FAD as Coenzymes?

NAD⁺ (derived from Niacin/Vitamin B₃) and FAD (derived from Riboflavin/Vitamin B₂) function as electron carriers. They accept hydrogen (electrons and protons) during oxidation reactions and donate them to the electron transport chain (ETC) to help generate ATP.