Chapter 3: Microbial Metabolism

Overview

• Metabolism: Sum of all chemical reactions in a cell.
  • Catabolism: Breaking down molecules, releases energy, stored as ATP.
  • Anabolism: Building molecules, requires energy from ATP.
  • Metabolic Pathway: Series of reactions in sequence.

Metabolism's Purpose

• Allows cells to grow, reproduce, and maintain homeostasis.

Enzymes

• Proteins that catalyze reactions, increasing reaction speed without being consumed.
• Enzymes' names typically end in "-ase".
• May require cofactors for function.

Nutrient Intake and Cell Composition

• Cells mainly consist of water (75%) and macromolecules.
  • Macromolecules: Proteins, lipids, nucleotides, polysaccharides.
  • Require macronutrients and micronutrients.

Macronutrients

• Major: Carbon, hydrogen, oxygen, nitrogen, phosphorus.
• Minor: Sulfur, potassium, magnesium, selenium, sodium, calcium.

Micronutrients

• Required in small amounts; includes trace metals and growth factors.

Types of Organisms by Nutrient Sources

• Carbon Source:
  • Heterotrophs: From organic molecules.
  • Autotrophs: From inorganic molecules (e.g., CO2).
• Energy Source:
  • Chemotrophs: From chemicals.
    • Chemoorganotrophs: From organic compounds.
    • Chemolithotrophs: From inorganic compounds.
  • Phototrophs: From light.
    • Oxygenic: Produce oxygen.
    • Anoxygenic: Do not produce oxygen.

Energy and Reaction Dynamics

• Free Energy (G): Energy available to do work.
  • Exergonic Reactions: Release energy (negative ΔG).
  • Endergonic Reactions: Require energy (positive ΔG).
• Activation Energy: Energy needed to initiate a reaction.
• Enzymes: Lower activation energy, increasing reaction rates.

ATP - Adenosine Triphosphate

• Primary energy carrier.
• Hydrolysis releases energy (exergonic).
• Synthesized through redox reactions involving electron transfers.

Catabolism of Carbohydrates

• Glycolysis: Converts glucose to pyruvate, produces ATP and NADH.
• Fermentation: Anaerobic, regenerates NAD+ for glycolysis.
• Respiration: Aerobic or anaerobic, involves:
  • Pyruvate Oxidation: Converts pyruvate to acetyl-CoA.
  • Krebs Cycle: Completes glucose oxidation, generates electron carriers.
  • Oxidative Phosphorylation: Uses electron transport chain to form ATP.

Anabolism

• Gluconeogenesis: Formation of glucose from non-carbohydrate sources.
• Pentose Phosphate Pathway: Generates five-carbon sugars, NADPH.
• Amino Acid & Nucleotide Synthesis: Utilizes intermediates from glycolysis/Krebs cycle.
• Fat Synthesis: Formation of fatty acids and glycerol for lipids.

Integration of Metabolism

• Amphibolic Pathways: Serve both catabolic and anabolic functions.
• Cells regulate pathway direction by enzyme availability.