Enzymes

Sum of all chemical reactions in an organism to sustain life.

• Anabolism: Building up complex molecules from simpler ones (uses energy). Example: Photosynthesis, Protein synthesis.
• Catabolism: Breakdown of complex molecules into simpler ones (releases energy). Example: Cellular Respiration, Lipolysis (breakdown of lipids).

Definition: Biological catalysts (mostly proteins) that speed up chemical reactions without being consumed.

Characteristics:

• Protein Nature: Made of amino acids (globular structure).
• Specificity: Specific to one reaction and substrate (e.g., Amylase breaks starch).
• Active Site: Catalytic region where substrate binds.
• Intracellular vs Extracellular: Work inside cells (respiration enzymes) or secreted outside (digestive enzymes like Pepsin).

Non-protein molecules required for enzyme activity.

• Inorganic: Metal ions (e.g., $Fe^{2+}$, $Mg^{2+}$).
• Organic:
  • Prosthetic Group: Tightly bound (e.g., Haem group).
  • Coenzyme: Loosely bound (e.g., Vitamins, NAD).

Enzyme + Substrate -> ES Complex -> Enzyme + Product

• Lock and Key Model (Emil Fischer, 1894): Active site is rigid; substrate fits exactly like a key in a lock.
• Induced Fit Model (Daniel Koshland, 1958): Active site is flexible; it changes shape to mold around the substrate for better fit. (More accepted model).

• Temperature: Rate increases with temp up to Optimum Temperature (37°C for humans). High temp causes Denaturation (loss of shape).
• pH: Each enzyme has an Optimum pH. Change in pH affects ionization of amino acids. Example: Pepsin (Acidic, pH 2), Trypsin (Alkaline, pH 8).
• Substrate Concentration: Rate increases with substrate until all active sites are occupied (Saturation). Further increase has no effect.

Substances that decrease enzyme activity.

• Competitive Inhibitors: Resemble substrate, compete for Active Site (e.g., Antibiotics, Sulpha drugs).
• Non-Competitive Inhibitors: Bind elsewhere (Allosteric site), change enzyme shape making active site unfit (e.g., Heavy metals, Cyanide).

• Food Industry: Starch breakdown (White bread, bun).
• Brewing: Fermentation (Yeast).
• Paper Industry: Lower viscosity of starch.
• Biological Detergents: Protease (removes protein stains), Amylase (removes starch residues).