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Microbial Metabolism Chapter 10 Overview

Metabolism Overview

• Definition: The sum of all chemical reactions within a cell.

• Components:

  • Anabolism: Building molecules; requires energy.

  • Catabolism: Breaking down molecules; releases energy.

Relative Complexity of Molecules

• Catabolism: Breaks down complex molecules (e.g., glucose) to yield energy.

• Anabolism: Synthesizes complex molecules from simpler ones (e.g., amino acids like Lysine).

Roles of Enzymes in Metabolism

• Enzymes: Biological catalysts, lower activation energy.

• Substrates: Reactants on which enzymes act.

• Product Release: Enzymes release products and can catalyze other reactions.

• Structure:

  • Simple Enzymes: Made entirely of protein.

  • Conjugated Enzymes (Holoenzymes): Composed of a protein portion (apoenzyme) and a cofactor (metal ions or coenzymes).

Enzyme Functionality

• Active Site: Where substrate binds and reactions occur.

• Enzyme-Substrate Interaction: Induced-fit model changes enzyme shape upon substrate binding.

Enzyme Regulation

• Constitutive Enzymes: Constant amounts regardless of substrate.

• Regulated Enzymes: Produced based on substrate presence; can be repressed.

Enzyme Inhibition Types

• Competitive Inhibition: Similar molecules compete for the active site.

• Noncompetitive Inhibition: Inhibitor binds elsewhere, altering enzyme shape.

Allosteric Regulation

• Allosteric Inhibitor/Activator: Changes enzyme activity.

• Feedback Inhibition: End product inhibits early pathway steps.

Location of Enzyme Action

• Exoenzymes: Move outside the cell to break down larger molecules.

• Endoenzymes: Function within the cell and comprise most metabolic pathways.

Types of Enzymes

• Oxidoreductases: Catalyze oxidation-reduction reactions.

• Transferases: Transfer functional groups.

• Hydrolases: Break bonds through hydrolysis.

• Lyases, Isomerases, Ligases: Involved in various metabolic processes.

Energy in Cells

• ATP (Adenosine Triphosphate): Main energy currency; drives cellular activities.

• Structure: Adenine, ribose, and three phosphates; energy released by breaking bonds.

• Regeneration: ATP is regenerated through phosphorylation.

Coupling Reactions

• Exergonic Reactions: Release energy; power endergonic reactions which require energy.

Simplified Model of Energy Production

• Redox Reactions: Oxidation and reduction events. Reduced compounds have more energy.

• Electron Carriers: NAD+ and FAD transfer electrons in metabolic processes.

Respiration Pathways Overview

• Aerobic Respiration: Uses oxygen, yielding maximum ATP.

• Anaerobic Respiration: Varies in ATP yield (2-36) with alternative acceptors.

• Fermentation: Generates energy without respiration (2 ATP).

Glycolysis Overview

• Location: Cytoplasm; converts glucose into pyruvate.

• Energy Yield: Net gain of 2 ATP and 2 NADH.

Pyruvate Fate

• Aerobic: Converts to acetyl-CoA for the Krebs cycle.

• Anaerobic: Becomes lactic acid or ethanol and CO₂.

Krebs Cycle

• Location: Mitochondrial matrix (eukaryotes); cytoplasm (prokaryotes).

• Outputs per Acetyl-CoA: 3 NADH, 1 FADH₂, 1 ATP, and 2 CO₂.

Electron Transport Chain (ETC)

• Location: Inner mitochondrial membrane; uses NADH and FADH₂.

• Final Electron Acceptor: Oxygen, producing water.

Energy Production Summary

• Total ATP: Glycolysis - 2 ATP; Krebs Cycle - 2 ATP; Oxidative Phosphorylation - up to 34 for a maximum of 38 per glucose.

Anaerobic Respiration

• Uses alternative electron acceptors; varies in end products.

Fermentation

• Lacks an electron transport chain; relies on substrate-level phosphorylation.

• Types: Lactic Acid and Alcoholic fermentation; yields 2 ATP.

Fermentation by Microbes

• Lactic Acid Fermentation: Glucose → Pyruvate → Lactic Acid.

• Alcoholic Fermentation: Glucose → Pyruvate → Ethanol + CO₂.

Homolactic vs Heterolactic Fermentation

• Homolactic: Produces lactic acid only; yields 2 ATP.

• Heterolactic: Produces lactic acid, ethanol, and CO₂; lower ATP yield.

Mixed Acid Fermentation

• Who: Common in Enterobacteriaceae (e.g., E. coli).

Amphibolism

• Integrates anabolic and catabolic pathways (e.g., Acetyl-CoA for fatty acid synthesis).

Lipid and Protein Catabolism

• Lipid: Breaks down into fatty acids and glycerol; involves lipases.

• Protein: Degrades proteins into amino acids; facilitated by proteases.

Photosynthesis Overview

• Light-Dependent Reactions: Produce energy using sunlight.

• Light-Independent Reactions: Synthesize glucose from CO₂.

Photosynthesis in Eukaryotes

• Occurs in chloroplasts; thylakoid membranes capture light.

Calvin Cycle Overview

• Converts CO₂ into glucose using ATP and NADPH in the stroma.

Summary of Key Points

• Metabolism: Total cellular reactions of anabolism and catabolism.

• Enzyme Function: Lowers activation energy; crucial for pathways.

• Energy Production: Through ATP; includes glycolysis and Krebs cycle.

Fill in the Blank Worksheet on Microbial Metabolism

1. Metabolism: The sum of all chemical reactions within a cell, consisting of ____________ (building molecules; requires energy) and ____________ (breaking down molecules; releases energy).

2. Enzymes: Biological catalysts that lower ____________.

3. Active Site: The region where the ____________ binds and reactions occur.

4. ATP (Adenosine Triphosphate) is the main ____________ currency in cells.

5. Glycolysis occurs in the ____________ and converts glucose into ____________ with a net gain of 2 ATP and 2 NADH.

6. The Krebs Cycle occurs in the ____________ matrix (eukaryotes) and produces 3 NADH, 1 FADH₂, 1 ATP, and ____________ CO₂ per acetyl-CoA.

7. Fermentation generates energy without ____________ and yields 2 ATP.

8. Electron carriers like ____________ and FAD transfer electrons in metabolic processes.

9. In Homolactic Fermentation, glucose is converted into ____________ acid only; yields 2 ATP.

10. The Calvin Cycle converts CO₂ into glucose using ____________ and NADPH.