Lecture Notes: Microbial Metabolism

Introduction to Metabolism

• Metabolism: All chemical reactions and physical workings inside the cell.
• Two main processes:
  • Anabolic Reactions:
    • Biosynthesis: Synthesis of cell molecules and structures from smaller subunits.
    • Requires energy input.
    • Example: Protein synthesis from amino acids.
  • Catabolic Reactions:
    • Breakdown: Larger molecules broken into smaller subunits.
    • Releases energy, often stored as ATP.
    • Example: Glucose breakdown for ATP production.

Metabolic Accomplishments

• Assembly: Small molecules into larger macromolecules using ATP (anabolic).
• Degradation: Macromolecules into smaller molecules, yielding energy (catabolic).
• Energy Conversion: Energy stored and spent in the form of ATP and heat.
• ATP Production: Catabolism of glucose can produce 34-38 ATPs.
  • Heat is a byproduct and not a usable form of energy.

Simplified Metabolic Model

• Nutrients: Derived from outside cell or internal pathways.
• Catabolic Pathways: Glycolysis, Krebs cycle, electron transport chain, fermentation (anaerobic).
• Precursor Molecules: Used for anabolic reactions to make proteins, sugars, nucleic acids, fats.
• Cell Division: Anabolic processes can lead to cell formation.

Role of Enzymes

• Catalysts: Speed up chemical reactions without being consumed.
• Composition: Made of proteins; may require cofactors.
• Function: Lower activation energy, speeding up reactions.
• Characteristics:
  • Specificity for substrates.
  • Recycled and function in low concentrations.
  • Affected by temperature and pH; extremes can denature.

Enzyme Substrates and Activity

• Substrates: Reactive molecules enzymes act on.
• Enzymatic Structure:
  • Simple Enzymes: Protein alone.
  • Conjugated/Holoenzymes: Protein + non-protein molecules.
  • Cofactors: Non-protein (metal ions, coenzymes).
  • Active Site: 3D site where substrate binds.

Classes of Enzymes

• Oxidoreductases: Transfer electrons.
• Transferases: Transfer functional groups.
• Hydrolases: Cleave bonds with water.
• Lyases: Add/remove groups from double bonds.
• Isomerases: Change isomeric forms.
• Ligases: Catalyze bond formation with ATP input.

Enzyme Regulation

• Competitive Inhibition: Inhibitor occupies active site, blocking substrate.
• Non-Competitive Inhibition: Inhibitor binds elsewhere, changing active site shape.
• Enzyme Repression: Stops enzyme synthesis when excess product is present.
• Enzyme Induction: Enzymes produced only when substrates are present.

Conclusion

• Enzymes are critical for metabolic pathways and energy production in cells.
• Understanding enzyme regulation and function is key to studying metabolism.