Microbial Metabolism

Metabolism Overview

• Metabolism: All chemical reactions in a cell.

• Catabolism: Breakdown of molecules, releases energy.

• Anabolism: Synthesis of molecules, requires energy.

ATP and Phosphorylation

• ATP: Main energy currency of the cell.

• Phosphorylation Types:

  Substrate-level (– Phosphate added from another organic molecule),

  oxidative phosphorylation – Energy released by electron transport is used,

  photophosphorylation – Light energy is used.

• Role of ATP: Couples energy-releasing and energy-consuming reactions.

Oxidation-Reduction Reactions

1. Oxidation is the removal of electrons (e-) from a molecule

a. This releases energy

2. Reduction is the addition of electrons (e-) to a molecule

a. This stores energy

3. Oxidation and reduction reactions are coupled so that one molecule loses an

e-, which is then transferred to another molecule. (aka Redox reactions)

Enzymes and Enzyme Activity

• Enzyme: Biological catalyst, speeds up reactions.

• Substrate: Molecule acted upon by enzyme.

• Active Site: Region where substrate binds.

• Specificity: Enzymes act on specific substrates.

• Cofactor: Non-protein helper (metal ion).

• Coenzyme: Organic cofactor (e.g., NAD+).

• Activation Energy: Enzymes lower the energy required for reactions.

• Factors Affecting Activity: Temperature, pH, substrate/enzyme concentration.

• Inhibition: Competitive (inhibitor binds active site), Noncompetitive (inhibitor binds elsewhere).

Carbohydrate Metabolism and Respiration

• Carbohydrate Metabolism: Breakdown of sugars for energy.

• Aerobic Respiration Stages: Glycolysis, Krebs cycle, Electron Transport Chain (ETC).

• Glycolysis: Glucose to pyruvate; produces ATP and NADH.

• Krebs Cycle: Oxidizes acetyl-CoA; produces NADH, FADH2, ATP, CO2.

• ETC: Transfers electrons to oxygen; generates proton gradient for ATP synthesis (oxidative phosphorylation).

• Electron Carriers: NADH, FADH2, cytochromes, ubiquinone.

• Chemiosmosis: Proton gradient drives ATP synthase to make ATP.

• Net Energy: Aerobic respiration yields more ATP than fermentation.

• Aerobic vs. Anaerobic Respiration: Final electron acceptor is oxygen (aerobic) or another molecule (anaerobic).

• Fermentation: Incomplete oxidation of glucose; end products include lactic acid, ethanol.

• Fats/Proteins: Can be catabolized to enter glycolysis or Krebs cycle.

Photosynthesis and Amphibolic Pathways

• Photosynthesis: Conversion of light energy to chemical energy.

• Light-Dependent Reactions: Produce ATP and NADPH.

• Light-Independent Reactions (Calvin Cycle): Use ATP/NADPH to fix CO2 into sugars.

• Amphibolic Reactions: Pathways that function in both catabolism and anabolism.

Example Table: Comparison of Gram-Positive and Gram-Negative Cell Walls

Additional info: Where the original study guide listed only learning objectives, academic context and explanations have been added to create a self-contained study guide suitable for exam preparation.