Chapter 21: Enzymes and Vitamins

General Characteristics of Enzymes

  • Enzymes are biological catalysts, primarily proteins.

  • Present in thousands of different forms within each cell.

  • Accelerate reactions by lowering activation energy.

  • Not consumed during reactions.

  • Some enzymes are ribonucleic acids (RNA).

Enzyme Structure

  • Two types of enzymes: Simple (only amino acids) and Conjugated (protein + non-protein part).

  • Holoenzyme = apoenzyme + cofactor/coenzyme (activator).

Nomenclature and Classification of Enzymes

  • Enzymes named based on the type of reaction and substrate.

  • Naming conventions include:
      1. Suffix -ase.
      2. Type of reaction as a prefix (e.g., oxidase).
      3. Substrate type in the name.

  • Six major classes:
      1. Oxidoreductases
      2. Transferases
      3. Hydrolases
      4. Lyases
      5. Isomerases
      6. Ligases

Enzyme Models of Action

  • Active site: area of the enzyme responsible for substrate binding and catalysis.

  • Models of substrate binding include: Lock-and-Key and Induced Fit models.

Enzyme Specificity

  • Absolute specificity: catalyzes only one substrate.

  • Stereochemical specificity: differentiates between stereoisomers.

  • Group specificity: acts on similar compounds.

  • Linkage specificity: focuses on specific types of bonds.

Factors Affecting Enzyme Activity

  1. Temperature: Higher temp increases activity until denaturation occurs (optimum at 37°C).

  2. pH: Activity optimal between 7.0-7.5 (exceptions include pepsin at pH 2.0).

  3. Substrate concentration: Increased substrate boosts activity until saturation.

  4. Enzyme concentration: More enzyme leads to higher reaction rates.

Enzyme Inhibition

  • Types: Competitive (competes with substrate) and Non-competitive (binds elsewhere on enzyme).

  • Irreversible inhibitors permanently deactivate enzymes.

Regulation of Enzyme Activity

  • Mechanisms include feedback control, proteolytic enzymes, and covalent modification (e.g., phosphorylation).

  • Allosteric enzymes: have multiple binding sites for regulators that can activate or inhibit.

Vitamins as Enzyme Cofactors

  • Vitamins are organic compounds essential for enzymatic function.

  • Classified into Water-Soluble (B-vitamins, C) and Fat-Soluble (A, D, E, K).

  • Vitamin deficiencies lead to health issues (e.g., Vitamin C deficiency causes scurvy).