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Chapter 5: Microbial Metabolism

Introduction to Metabolism

• Metabolism: Refers to the buildup and breakdown of nutrients within a cell.

  • These chemical reactions provide energy and create substances that sustain life.

  • Metabolism can result in both beneficial and harmful effects, such as disease and food spoilage.

Catabolic and Anabolic Reactions

• Catabolic Reactions:

  • Function: Break down complex molecules.

  • Purpose: Provide energy and building blocks for anabolic reactions.

  • Nature: Exergonic (release energy).

• Anabolic Reactions:

  • Function: Build complex molecules from simpler ones.

  • Nature: Endergonic (require energy).

• ATP (Adenosine Triphosphate): Serves as an energy carrier, facilitating the transfer of energy between catabolic and anabolic processes.

Enzymes and Their Role

• Enzymes: Biological catalysts that speed up chemical reactions without being consumed or altered.

  • They work on specific substrates, forming enzyme-substrate complexes, which lead to the formation of products.

• Factors affecting enzymatic activity:

  • Temperature: High temperatures can denature enzymes.

  • pH: Extreme pH levels can also lead to denaturation.

  • Substrate Concentration: High substrate concentrations can lead to maximum enzymatic activity, referred to as saturation.

Types of Inhibition

• Competitive Inhibition:

  • Inhibitors compete with substrates for the active site of enzymes.

  • May lead to reduced enzyme efficiency when the inhibitor is present.

• Noncompetitive Inhibition:

  • Inhibitors bind to an allosteric site, changing the enzyme's shape and rendering it nonfunctional.

Feedback Inhibition

• A type of allosteric inhibition where the end product of a biochemical pathway inhibits enzymes at earlier steps, preventing overproduction.

Ribozymes

• RNA molecules that act as catalysts, involved in various cellular processes such as splicing RNA and protein synthesis, not consumed in reactions.

Oxidation-Reduction Reactions

• Oxidation: Loss of electrons (and protons), often termed dehydrogenation.

• Reduction: Gain of electrons.

• Together, these reactions are termed redox reactions.

ATP Generation

• Substrate-Level Phosphorylation: ATP can be generated directly from ADP by the addition of a high-energy phosphate group.

• Oxidative Phosphorylation: Involves transferring electrons through an electron transport chain, utilizing chemiosmosis to produce ATP.

• Photophosphorylation: Occurs in photosynthetic organisms, where light energy is converted into chemical energy (ATP).

Metabolic Pathways

• Organized sequences of enzymatically catalyzed reactions that extract energy from organic compounds and convert it into ATP.

• Includes glycolysis, Krebs cycle, and the electron transport chain.

Carbohydrate Catabolism

• Glycolysis: The process of breaking down glucose to pyruvic acid, yielding ATP and NADH.

  • Stages:

    • Preparatory stage: Consumes 2 ATP to split glucose.

    • Energy-conserving stage: Produces 4 ATP and 2 NADH, resulting in a net gain of 2 ATP.

• Krebs Cycle: Follows glycolysis, further oxidizing pyruvic acid and generating NADH, FADH2, and ATP.

• Electron Transport Chain: Producing the bulk of ATP through chemiosmosis.

Anaerobic Respiration

• Occurs when the final electron acceptor is not oxygen, leading to less energy yield compared to aerobic respiration.

• Utilizes alternative molecules like nitrate and sulfate as terminal electron acceptors.

Fermentation

• A process that releases energy from organic molecules without using the Krebs cycle or electron transport chain, yielding minimal ATP.

• Types of fermentation:

  • Lactic Acid Fermentation: Converts pyruvic acid into lactic acid.

  • Alcohol Fermentation: Converts pyruvic acid into ethanol and CO2.

Lipid and Protein Catabolism

• Lipids are broken down into glycerol and fatty acids, which enter glycolysis or Krebs cycle.

• Proteins are degraded into amino acids, which can also enter metabolic pathways after deamination.

Biochemical Tests for Bacterial Identification

• Fermentation Test: To identify bacteria that produce acid from carbohydrates or proteins.

• Oxidase Test: Determines the presence of cytochrome c oxidase in bacteria.

Photosynthesis

• Light-Dependent Reactions: Convert light energy into ATP and NADPH.

• Light-Independent Reactions (Calvin-Benson Cycle): Use ATP and NADPH to convert CO2 into sugar.

• Differentiation between oxygenic and anoxygenic photosynthesis based on oxygen production.

Metabolic Diversity

• Various organisms are categorized based on their energy sources (light, organic/inorganic compounds) and metabolic pathways.

Summary

• Energy Production: Summary of ATP generation through various metabolic processes including catabolism of carbohydrates, lipids, and proteins, alongside the importance of metabolic pathways.

Conclusion

• The integration of both anabolic and catabolic pathways ensures the efficient use of energy within cells, supporting various cellular functions and sustaining life.