4 Students Spr 25 Chapter 5

Microbial Metabolism Overview

• Metabolism: Sum of all chemical reactions in an organism

• Determined by enzymes, which are encoded by organism's genes

  • 1. Acquire nutrients (absorptive: combination of passive and active)

  • 2. Breakdown of nutrients - Catabolic pathways • Requires energy but releases more energy that it uses = exergonic reactions• Synthesizes ATP to store excess energy; some is lost as heat• Requires enzymes to catabolize nutrients into ”precursor metabolites”

  • 3. Synthesis of macromolecules - Anabolic pathways• Requires energy = endergonic reactions• Hydrolyzes ATP to release energy required • Requires enzymes • Polymerization reactions

• Metabolic Pathways: Sequence of enzyme-catalyzed chemical reactions. Enzymes are encoded by genes (reflects genotype of organism)

Chemical Reactions and Enzymes•

Catalysts speed up chemical reactions without being altered• Enzymes are biological catalysts• Substrate is transformed and rearranged into products,which are released from the enzyme

• Enzyme is unchanged and can react with other substrates

• Activation energy is needed to disrupt chemical bonds• The required number of collisions with enough energy to bring about a reaction

• Activation energy required can be decreased by enzymes

• Reaction rate is the speed at which a reaction occurs• The frequency of collisions with enough energy to bring about a reaction

Learning Objectives

• Define metabolism, anabolism, and catabolism

• Role of ATP in metabolism

• Components and action mechanisms of enzymes

• Factors influencing enzymatic activity

• Understand and distinguish various metabolic pathways and reactions

Key Concepts in Metabolism

Definitions

• Anabolism: Building up reactions, requiring energy (endergonic)

• Catabolism: Breaking down reactions, releasing energy (exergonic)

  • Example: Breakdown of glucose to CO2 and H2O

  • 
    Catabolic apart

  • 
    Anabolic together

ATP's Role

• ATP serves as an energy intermediary

• Energy released during catabolism is stored in ATP

• ATP is used in anabolic reactions to synthesize cellular components

Enzyme Components and Action

Components

• Apoenzyme: Protein part of enzyme

• Cofactor: Non-protein chemical compounds

• Coenzyme: Organic molecules (e.g., vitamins like NAD+, FAD)

• Holoenzyme: Combination of apoenzyme and cofactor/coenzyme

Mechanism of Action

1. Active Site: Site where substrate binds

2. Enzyme-substrate complex forms, substrate is converted to product

3. Product is released, enzyme remains unchanged

4. Enzymes decrease activation energy for reactions

Factors Influencing Enzymatic Activity

• Temperature: High temp denatures proteins

• pH levels: Extreme pH can denature enzymes

• Substrate Concentration: High concentration can lead to maximum reaction rates

Inhibition of Enzymatic Activity

Types of Inhibition

• Competitive Inhibition: Inhibitor resembles substrate and competes for active site

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

Metabolic Pathways of ATP Generation

Types of Phosphorylation

1. Substrate-Level Phosphorylation: ATP generated during glycolysis

2. Oxidative Phosphorylation: Involves electron transport chain

3. Photophosphorylation: Use of light energy (photosynthesis)

Glycolysis

• Occurs in cytoplasm; does not require O2

• Stages of Glycolysis:

  • Energy Investment: Uses 2 ATP

  • Lysis: Produces glyceraldehyde 3-phosphate (G3P)

  • Energy Conserving: Produces 4 ATP & 2 NADH; net gain of 2 ATP

Krebs Cycle

• Acetyl-CoA combines with oxaloacetic acid to initiate cycle

• Produces NADH, FADH2, CO2, and ATP

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

Electron Transport Chain

• Chain of enzymes in the membrane facilitating ATP production via chemiosmosis

• Electrons transferred through carriers to ultimately produce water

• 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

  • Example electron acceptors: Nitrate, Sulfate, Carbonate

Fermentation

• Releases energy from the oxidation of organic molecules without O2

• Two types: Lactic Acid Fermentation and Alcoholic Fermentation

• Critical for regeneration of NAD+ to allow continued glycolysis

Biochemical Tests for Identification

• Identifies microorganisms using metabolic pathways, enzyme production, and biochemical reactions

• Examples include:

  • 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: Inorganic compounds as energy source

  • Chemoheterotrophs: Organic compounds for energy

  • Photoautotrophs: Light as energy source

Integration and Regulation of Metabolism

• Amphibolic Pathways: Function in both anabolism and catabolism, utilizing common intermediates

• Feedback inhibition allows for versatile control of metabolic pathways, enhancing efficiency and regulation

Conclusion

• Comprehensive understanding of metabolism is essential for identifying and categorizing microorganisms based on their biochemical pathways and energy use.