Notes on Enzymes and Vitamins

Enzymes and Enzyme Action

• Definition and Role of Enzymes

  • Biological catalysts that:
  • Increase the rate of reactions without being changed.
  • Lower the activation energy needed for reactions.
  • E.g., carbonic anhydrase reaction:
    $CO<em>2 + H</em>2O \rightleftharpoons HCO_3^- + H^+$

• Enzyme Structure

  • Most enzymes are proteins.
  • Enzymes bind to substrates at the active site, which interacts through:
  • Hydrogen bonds
  • Salt bridges
  • Hydrophobic interactions

Enzyme Specificity

• Enzymes show varying degrees of specificity:
  • Absolute Specificity: Catalyzes a single reaction with one substrate (e.g., urease).
  • Group Specificity: Catalyzes reactions for similar substrates (e.g., hexokinase).
  • Linkage Specificity: Catalyzes specific types of bonds (e.g., chymotrypsin for peptide bonds).

Enzyme Catalyzed Reactions

• Enzymes form an enzyme-substrate (E-S) complex, providing lower activation energy pathways.
  • Enzyme converts the substrate to a product, forming the enzyme-product (E-P) complex.

Models of Enzyme Action

• Lock-and-Key Model: Rigid substrate binds to a rigid enzyme.
• Induced-Fit Model: The active site changes shape to better fit the substrate, reducing activation energy more effectively.

Enzyme Classification

• Enzyme names typically end in -ase and describe either the substrate or the reaction.

Major Enzyme Classes

1. Oxidoreductases: Catalyze oxidation-reduction reactions.
   • E.g., alcohol dehydrogenase.
2. Transferases: Transfer functional groups.
   • E.g., kinases transfer phosphate groups.
3. Hydrolases: Catalyze hydrolysis reactions.
   • E.g., proteases break peptide bonds.
4. Lyases: Add or remove groups without hydrolysis.
   • E.g., decarboxylases remove CO₂.
5. Isomerases: Rearrange atoms within a substrate.
   • E.g., epimerases.
6. Ligases: Join substrates using ATP.
   • E.g., pyruvate carboxylase.

Factors Affecting Enzyme Activity

• Temperature: Enzymes have an optimum temperature (usually 37°C).
  • High temperatures can denature enzymes.
• pH: Each enzyme has an optimum pH (usually around 7.4 for human enzymes).
  • Extreme pH can lead to loss of enzyme structure.
• Concentration:
  • Increasing enzyme concentration usually increases reaction rate, provided substrate concentration is sufficient.
  • Substrate concentration affects rate until saturation is reached.

Regulation of Enzyme Activity

• Allosteric Regulation: Molecules bind at a different site than the substrate, changing the active site's shape.
  • Positive Regulator: Increases enzyme binding efficiency.
  • Negative Regulator: Decreases enzyme binding efficiency.
• Feedback Control: The end product of a reaction series can regulate the first step.
• Covalent Modification: Enzymes can be activated or deactivated through the addition or removal of functional groups.

Enzyme Inhibition

• Reversible Inhibition: Loss of activity can be restored.
  • Competitive Inhibitors: Compete with substrate for the active site.
  • Noncompetitive Inhibitors: Bind at a different site and alter enzyme shape.
• Irreversible Inhibition: Permanent loss of activity due to covalent bond formation.

Enzyme Cofactors and Vitamins

• Cofactors: Non-protein molecules (often metal ions) required for enzyme activity.
• Coenzymes: Small organic molecules, often derived from vitamins, that assist enzyme reactions.

Vitamins

• Essential for normal health, categorized into:
  • Water-Soluble: E.g., B vitamins and vitamin C (must be consumed regularly).

- Fat-Soluble: E.g., vitamins A, D, E, K (stored in the body; important for various bodily functions).

Classification and Functions of Vitamins:

• Water-Soluble Vitamins include B1 (Thiamine), B2 (Riboflavin), B3 (Niacin), etc.

• Fat-Soluble Vitamins include A (Retinol), D (Cholecalciferol), E (Tocopherol), and K (Menaquinone).

  • Each vitamin has specific sources and deficiency symptoms, crucial for maintaining overall health.