4 Students Spr 25 Chapter 5

Chapter 5: Microbial Metabolism Overview

Metabolism

• Definition: Sum of all chemical reactions in an organism.

• Determined by Enzymes: Enzymes, encoded by organism's genes, play a crucial role.

• Key Processes:

  1. Acquire Nutrients: Uses a combination of passive and active transport mechanisms.

  2. Breakdown of Nutrients:

     • Catabolic Pathways:

       • Energy-extracting processes, leading to exergonic reactions (energy releasing).

       • ATP is synthesized for energy storage but some is lost as heat.

       • Enzymes convert nutrients into precursor metabolites.

  3. Synthesis of Macromolecules:

     • Anabolic Pathways:

       • Energy-consuming reactions leading to endergonic reactions.

       • ATP is hydrolyzed to release energy for these processes.

       • Involves polymerization reactions.

Metabolic Pathways

• Definition: Sequence of enzyme-catalyzed chemical reactions.

• Role of Enzymes:

  • Enzymes are biological catalysts, speeding up reactions without being altered.

  • Substrates are transformed into products, released from enzymes that remain unchanged.

• Activation Energy:

  • Required to disrupt chemical bonds; enzymes lower this barrier to facilitate reactions.

  • Reaction rate depends on the frequency of collisions with sufficient energy.

Learning Objectives

• Define metabolism, anabolism, and catabolism.

• Understand the role of ATP in metabolism.

• Identify components and mechanisms of enzymes.

• Recognize factors influencing enzymatic activity.

• Distinguish various metabolic pathways and reactions.

Key Concepts in Metabolism

• Definitions:

  • Anabolism: Building reactions requiring energy; endergonic.

  • Catabolism: Breaking down reactions releasing energy; exergonic.

  • Example: Breakdown of glucose into CO2 and H2O.

Page 2: ATP and Enzymatic Mechanisms

ATP's Role

• Energy Intermediary: ATP is produced during catabolism and used in anabolic reactions.

• Energy Transfer: Catabolic reactions release energy stored in ATP for building cellular components.

Enzyme Components and Mechanism of Action

• Components:

  • Apoenzyme: The protein part of the enzyme.

  • Cofactor: Non-protein compounds required for enzyme activity.

  • Coenzyme: Organic molecules (e.g., NAD+, FAD) assisting enzymes.

  • Holoenzyme: Complete enzyme structure (apoenzyme + cofactor/coenzyme).

• Mechanism of Action:

  • Active Site: Where the substrate binds, forming an enzyme-substrate complex, resulting in product formation while leaving the enzyme unchanged.

Factors Influencing Enzymatic Activity

• Temperature: High temperature can lead to denaturation of enzymes.

• pH Levels: Extreme pH can affect enzyme activity and structure.

• Substrate Concentration: Higher concentrations can enhance reaction rates but reach saturation.

Inhibition of Enzymatic Activity

• Types of Inhibition:

  • Competitive Inhibition: Inhibitor resembles substrate, competing for the active site.

  • Non-Competitive Inhibition: Inhibitor binds to allosteric site, altering enzyme shape and function.

Metabolic Pathways of ATP Generation

• Types of Phosphorylation:

  • Substrate-Level Phosphorylation: ATP generated during glycolysis.

  • Oxidative Phosphorylation: Involves electron transport chain.

  • Photophosphorylation: Uses light energy (as in photosynthesis).

Glycolysis

• Location: Occurs in the cytoplasm and does not require O2.

• Stages of Glycolysis:

  • Energy Investment Phase: Uses 2 ATP.

  • Lysis Phase: Produces glyceraldehyde 3-phosphate (G3P).

  • Energy Conserving Phase: Results in production of 4 ATP and 2 NADH; net gain of 2 ATP.

Page 3: Krebs Cycle and ATP Production

Krebs Cycle

• Initiation: Begins when Acetyl-CoA combines with oxaloacetic acid.

• Outcomes: Produces NADH, FADH2, CO2, and ATP.

• Net Gain: For each glucose, 2 Acetyl-CoA yield 4 ATP, 6 NADH, and 2 FADH2.

Electron Transport Chain

• Function: Chain of enzymes in the membrane that aids in ATP production via chemiosmosis.

• Process: Electrons are transferred through carriers leading to water production.

• Proton Gradient: Created to drive ATP synthesis by ATP synthase.

Anaerobic vs. Aerobic Respiration

• Aerobic Respiration: Uses O2 as final electron acceptor, yielding more ATP.

• Anaerobic Respiration: Uses substances other than O2, producing less energy (e.g., nitrate, sulfate, carbonate).

Fermentation

• Definition: Releases energy from oxidation of organic molecules without O2.

• Types:

  • Lactic Acid Fermentation

  • Alcoholic Fermentation

• Importance: Critical for regenerating NAD+ to sustain glycolysis.

Biochemical Tests for Identification

• Purpose: Identifies microorganisms through metabolic pathways and enzyme production.

• Examples:

  • Blood Agar: Tests for hemolysis.

  • MacConkey Agar: Tests lactose fermentation in gram-negative bacteria.

  • Urease Test: Tests for urease production.

Classification of Organisms

• Metabolic Classifications:

  • Chemoautotrophs: Use inorganic compounds for energy.

  • Chemoheterotrophs: Use organic compounds for energy.

  • Photoautotrophs: Use light as an energy source.

Integration and Regulation of Metabolism

• Amphibolic Pathways: Function as both anabolic and catabolic processes utilizing common intermediates.

• Feedback Inhibition: A regulatory mechanism for metabolic pathways, enhancing efficiency.

Conclusion

• A comprehensive understanding of metabolism is crucial for identifying and categorizing microorganisms based on their biochemical pathways and energy utilization.