Enzymes and Vitamins - Detailed Study Notes

Overview of Enzymes

• Enzymes are biological catalysts.
  • Increase the rate of chemical reactions by altering reaction pathways.
  • Remain unchanged throughout the reaction.
  • Lower the activation energy required for reactions.

1. Enzyme Action

• Role of Enzymes:
  • Catalyze reactions, allowing for quick transformations of substrates into products.
  • Example: Carbonic anhydrase converts carbon dioxide and water into bicarbonate and vice versa.

2. Enzymes and Active Sites

• Structure of Enzymes:
  • Enzymes, mostly globular proteins, possess a unique 3D shape that allows substrate recognition and binding.
  • Enzymatic activity occurs in the active site where substrate binding happens.
  • Involves interactions such as hydrogen bonds, salt bridges, and hydrophobic interactions with specific amino acid residues.
• Example: Lactase has an active site that accommodates lactose, facilitating its hydrolysis.

3. Specificity of Enzymes

• Types of Enzyme Specificity:
  • Absolute specificity: Catalyzes one particular reaction for a single substrate.
  • Example: Urease catalyzes hydrolysis of urea.
  • Group specificity: Catalyzes the reaction involving similar substrates.
  • Example: Hexokinase transfers phosphate to hexoses.
  • Linkage specificity: Catalyzes reactions involving a specific type of bond.
  • Example: Chymotrypsin hydrolyzes peptide bonds.

4. Enzyme-Catalyzed Reactions

• Formation of Enzyme-Substrate (ES) Complex:
  • The ES complex lowers the activation energy, providing an alternative reaction pathway.
• Formation of enzyme-product (EP) complex happens post-reaction.

5. Models of Enzyme Action

• Two primary models:
  • Lock-and-Key Model: Rigid substrates fitting into rigid enzymes.
  • Induced-Fit Model: The active site adapts to the substrate shape, assisting in the reaction process.

6. Classification of Enzymes

• Enzymes named based on the compound they work on or the reaction they catalyze, commonly ending in -ase.
• Types of Enzymes:
  1. Oxidoreductases: Catalyze oxidation-reduction reactions.
  • Example: Oxidases.
  1. Transferases: Transfer functional groups between substrates.
  • Example: Transaminases.
  1. Hydrolases: Catalyze hydrolysis reactions.
  • Example: Proteases.
  1. Lyases: Add or remove groups without hydrolysis.
  2. Isomerases: Catalyze rearrangements within substrates.
  3. Ligases: Join two substrates using ATP energy.

7. Factors Affecting Enzyme Activity

• Enzyme activity is influenced by:
  • Temperature: Most active at optimum temp; denatures at high temp.
  • Temperatures vary by organism, e.g., thermophiles thrive in hotter environments.
  • pH: Optimal pH maintains enzyme tertiary structure; extremes lead to loss of activity.
  • Example: Pepsin operates at pH 1.5-2, while trypsin functions best at pH 7.7-8.0.
  • Enzyme Concentration: Increased concentration raises reaction rate.
  • Substrate Concentration: Higher substrate concentration increases reaction rate until saturation is reached.

8. Regulation of Enzyme Activity

• Regulatory Mechanisms:
  • Allosteric Regulation: Binding of activators or inhibitors at sites other than the active site changes enzyme activity.
  • Feedback Control: End products inhibit or activate enzyme activity through binding.
  • Covalent Modification: Enzyme activation/deactivation through addition/removal of groups, e.g., phosphorylation.

9. Isoenzymes and Diagnostic Uses

• Isoenzymes are enzyme variants that catalyze the same reactions.
  • Diagnostic significance in healthcare, e.g., elevated lactate dehydrogenase (LDH) levels indicating tissue damage.

10. Enzyme Inhibition

• Types of Inhibitors:
  • Reversible Inhibition: Loss of activity that can be restored; includes competitive (competes for active site) and noncompetitive (binds elsewhere).
  • Irreversible Inhibition: Permanent loss of activity due to covalent bond formation with enzyme.
  • Example: Antimetabolites used in medicine as competitive inhibitors.

11. Enzyme Cofactors and Vitamins

• Cofactors: Non-protein components needed for enzyme activity.
  • Coenzymes: Organic cofactors, e.g., vitamins.
  • Importance of specific vitamins in enzyme function, e.g., ascorbic acid (Vitamin C) is crucial for collagen synthesis.
• Fat-Soluble and Water-Soluble vitamins have distinct roles in human health and enzyme activity.