Microbial Metabolism

Introduction

Microbial metabolism encompasses the chemical processes that occur within microorganisms, enabling them to grow, reproduce, and respond to their environments. These processes include the breakdown and synthesis of molecules, energy production, and the regulation of metabolic pathways.

• Enzymes

• Oxidation and Reduction Reactions

• Carbohydrate Metabolism (Respiration and Fermentation)

• Lipid and Protein Metabolism

• Photosynthesis

• Metabolic Diversity Among Organisms

Enzymes

Key Terms and Concepts

Enzymes are biological catalysts that accelerate chemical reactions in cells. They are essential for metabolism, which is the sum total of all chemical reactions in an organism.

• Metabolism: The complete set of chemical reactions in a cell or organism.

• Catabolic Reaction: Breaks down complex molecules to release energy; energy-generating.

• Anabolic Reaction: Consumes energy to build complex molecules from simpler ones; energy-consuming.

ATP Coupling of Anabolic and Catabolic Reactions

ATP (adenosine triphosphate) acts as the energy currency of the cell, coupling energy-releasing catabolic reactions to energy-consuming anabolic reactions.

• Catabolic reactions transfer energy from complex molecules to ATP.

• Anabolic reactions use ATP to build complex molecules.

• ATP is regenerated from ADP and inorganic phosphate ().

Generation of ATP

ATP is generated by the phosphorylation of ADP. There are two main mechanisms:

• Oxidative Phosphorylation: Energy from electron transfer is used to add a phosphate to ADP.

• Photophosphorylation: Light energy is used to generate ATP in photosynthetic organisms.

Equation:

Enzyme Structure and Function

• Apoenzyme: The protein portion of an enzyme (inactive alone).

• Cofactor: Non-protein component; can be inorganic (e.g., iron, zinc).

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

• Holoenzyme: The complete, active enzyme (apoenzyme + cofactor).

Enzyme Classification

• Oxidoreductase: Catalyzes oxidation-reduction reactions.

• Transferase: Transfers functional groups.

• Hydrolase: Catalyzes hydrolysis reactions.

• Lyase: Removes atoms without hydrolysis.

• Isomerase: Rearranges atoms within a molecule.

• Ligase: Joins molecules using ATP.

Factors Influencing Enzyme Activity

• Temperature: High temperatures can denature enzymes.

• pH: Extreme pH values can denature enzymes.

• Substrate Concentration: Affects reaction rate.

• Inhibitors: Can decrease enzyme activity (competitive and non-competitive).

Enzyme Inhibition

• Competitive Inhibition: Inhibitor binds to the active site, blocking substrate.

• Non-competitive Inhibition: Inhibitor binds elsewhere, changing enzyme shape and preventing substrate binding.

Ribozymes

• Ribozymes: RNA molecules with catalytic activity, involved in cutting and splicing RNA.

Oxidation and Reduction Reactions

Redox Reactions in Metabolism

Oxidation-reduction (redox) reactions are central to energy production in cells.

• Oxidation: Loss of electrons.

• Reduction: Gain of electrons.

• Redox Reaction: An oxidation reaction paired with a reduction reaction.

Oxidative Phosphorylation

• Energy released from electron transfer is used to generate ATP via the electron transport chain.

Photophosphorylation

• Light energy excites electrons in chlorophyll, which are transferred through carrier molecules to generate ATP.

Carbohydrate Catabolism

Overview

Carbohydrate catabolism is the breakdown of carbohydrates to release energy. The two main processes are respiration and fermentation.

• Respiration: Oxygen-dependent; includes glycolysis, Krebs cycle, and electron transport chain.

• Fermentation: Oxygen-independent; produces less ATP.

Glycolysis

• Oxidation of glucose to pyruvic acid.

• Two stages: preparatory (uses 2 ATP) and energy-conserving (produces 4 ATP, net gain 2 ATP).

• Produces 2 NADH.

Krebs Cycle

• Pyruvic acid is converted to Acetyl CoA.

• Produces 8 NADH and 2 FADH2.

Electron Transport Chain

• Series of carrier molecules that transfer electrons, producing up to 34 ATP.

Summary of Aerobic Respiration

• Net output: 6 CO2, 38 ATP.

Fermentation

• Releases energy from organic molecules without oxygen.

• Produces small amounts of ATP.

• End products: acids, alcohols, CO2.

• Examples: lactic acid fermentation, alcohol fermentation.

Lipid and Protein Catabolism

Lipid Catabolism

• Lipids are broken down to glycerol and fatty acids.

• Products enter glycolysis and Krebs cycle for energy production.

Protein Catabolism

• Proteins are digested to amino acids.

• Amino acids undergo deamination, decarboxylation, and other modifications to enter the Krebs cycle.

Photosynthesis

Photosynthetic Processes

• Light-dependent reactions: Photophosphorylation generates ATP using light energy.

• Light-independent reactions: The Calvin-Benson cycle uses ATP to fix CO2 into sugars.

Metabolic Diversity Among Organisms

Classification by Energy and Carbon Source

Microorganisms are classified based on how they obtain energy and carbon.

Additional info: This classification is fundamental in microbiology and biochemistry for understanding how different organisms obtain energy and carbon for growth and metabolism.