Microbial Metabolism

Microbial Metabolism

• Definition of Metabolism: The synthesis (anabolism) and breakdown (catabolism) of nutrients within a cell, which provides energy and creates substances necessary for life.

Types of Metabolic Pathways

• Catabolic Pathways:

  • Function: Break down macromolecules into simpler components, releasing energy in the process.
  • Example: Glycolysis (glucose breakdown).
  • Energy released is stored as ATP.

• Anabolic Pathways:

  • Function: Build up macromolecules from simpler ones using energy.
  • Example: Protein synthesis (from amino acids).
  • Energy needed is derived from ATP breakdown.

• Energy Linkage: Catabolic reactions provide the energy required for anabolic processes, forming a cycle of energy use and storage.

Role of ATP in Metabolism

• ATP Usage:
  • ATP is vital for energy management in microbial cells; it both fuels and is produced through metabolic reactions.
  • Catabolic reactions are coupled with ATP synthesis, while anabolic reactions often involve ATP breakdown.

Enzymatic Action and Its Mechanisms

• Enzymes: Biological catalysts that speed up reactions by lowering the activation energy required; specific to substrates.

  • Active Site: The specific region of an enzyme where substrate binding occurs, forming an enzyme-substrate complex.
  • Turnover Number: Indicates how many substrate molecules an enzyme converts to product per second (ranges from 1 to 500,000).

• Collision Theory: Chemical reactions happen when molecules collide with enough energy to initiate a reaction. Enzymes increase the rate of reactions by facilitating these collisions.

Factors Affecting Enzyme Activity

• Temperature and pH: Extreme conditions can denature proteins (enzymes), thus impairing their functionality. Each enzyme has its optimal temperature and pH for maximum activity.
• Substrate Concentration: Higher concentrations can increase the rate of reaction until saturation is reached, where all active sites are occupied.
• Inhibitors: Substances that decrease enzyme activity. They can be competitive (compete with substrate for active site) or noncompetitive (bind to allosteric site, changing the enzyme's shape).

Feedback Inhibition

• Definition: A process wherein the end product of a metabolic pathway inhibits an enzyme involved in the pathway, preventing overproduction of end products.
• Mechanism: The end product binds to an allosteric site, altering the active site's shape and reducing enzyme activity.

Energy Production through Metabolism

• Oxidation-Reduction Reactions: Involve the transfer of electrons; oxidation is losing electrons, while reduction is gaining electrons. These reactions are essential in energy production pathways.
• Types of Energy Production:
  • Substrate-level Phosphorylation: Direct generation of ATP from ADP by transferring a phosphate during a reaction.
  • Oxidative Phosphorylation: Uses the electron transport chain to produce ATP, requiring oxygen as the final electron acceptor in aerobic respiration.
  • Photophosphorylation: Light-driven generation of ATP in photosynthetic organisms.

Key Pathways in Carbohydrate Catabolism

1. Glycolysis:

   • Breakdown of glucose to pyruvic acid, producing ATP and NADH.
   • Two phases: Preparatory and the energy-conserving stages.

2. Krebs Cycle:

   • Processes pyruvic acid to generate more electron carriers (NADH, FADH2) and a small amount of ATP.

3. Electron Transport Chain:

   • Transfers electrons from NADH and FADH2 to molecular oxygen, generating a proton gradient to drive ATP synthesis.

Anaerobic vs Aerobic Respiration

• Aerobic Respiration: Requires oxygen, yielding maximum energy (approximately 38 ATP per glucose molecule).
• Anaerobic Respiration: In absence of oxygen, yields less energy by utilizing other molecules as final electron acceptors.
  • Notable electron acceptors include nitrate (NO3⁻) and sulfate (SO42⁻).

Fermentation Processes

• Definition: A form of anaerobic metabolism that occurs when oxygen is absent, resulting in the partial oxidation of glucose.

• Types of Fermentation:

  • Lactic Acid Fermentation: Converts glucose into lactic acid.

  • Alcoholic Fermentation: Converts glucose into ethanol and carbon dioxide.

  • Fermentation is less efficient than respiration, yielding only 2 ATP per glucose molecule.

• Industrial Applications: Includes alcohol production (yeast) and lactic acid production (dairy).

Overall Summary

• Metabolism is an essential biological process linking energy production to cellular function and survival. Understanding microbial metabolism enhances insights into biotechnology and medicine.

• Key concepts such as ATP generation, enzyme function, and pathways like glycolysis and fermentation are fundamental in biological and biochemical studies.