Lecture Notes: Plasma Membrane and Microbial Metabolism

Plasma Membrane Overview

• Composition: Made up of a phospholipid bilayer with hydrophilic (polar) heads facing outwards and hydrophobic tails facing each other.
• Functions:
  • Selectively permeable: Controls entry and exit of substances.
  • Environmental signaling: Senses environmental changes.
  • Energy transformation in prokaryotes: Site where this occurs.

Transport Across the Plasma Membrane

Passive Transport

• Definition: Movement without energy (ATP).
• Types:
  • Diffusion: Movement from high to low concentration.
  • Osmosis: Diffusion of water.
  • Facilitated Diffusion: Requires a carrier protein but no energy; moves down concentration gradient.

Active Transport

• Definition: Movement that requires energy (ATP).
• Features: Can move substances against concentration gradient (low to high concentration).
• Types:
  • Group Translocation: Changes substance as it enters the cell.
  • Bulk Transport: Endocytosis, exocytosis, pinocytosis.

Osmosis and Tonicity

• Isotonic Environment: Solute concentration inside and outside is equal, causing no net water movement.
• Hypotonic Solution: Lower solute concentration outside; water enters the cell, risking cell lysis (bursting).
• Hypertonic Solution: Higher solute concentration outside; water exits the cell, leading to plasmolysis (shriveling).

Microbial Metabolism

Introduction to Metabolism

• Definition: Sum of chemical reactions in a cell.
• Purpose: Allows a cell to reproduce; identifies organisms through biochemical tests.

Types of Metabolic Reactions

Catabolism

• Definition: Breaking down large molecules into smaller ones.
• Energy Release: Produces ATP, hydrolytic reactions.
• Example: Cellular respiration.

Anabolism

• Definition: Building larger molecules from smaller ones.
• Energy Requirement: Needs ATP.
• Example: Dehydration synthesis.

ATP Synthesis

• Process: Involves phosphorylation; adding inorganic phosphate to ADP to form ATP.
• Reaction Coupling:
  • Anabolic reactions: Coupled to ATP breakdown.
  • Catabolic reactions: Coupled to ATP synthesis.

Enzymes

Role and Structure

• Definition: Biological catalysts made of proteins that speed up reactions by lowering activation energy.
• Structure:
  • Made of amino acids.
  • Enzyme action site known as active site.

Enzyme Function

• Substrate: Molecule on which an enzyme acts.
• Active Site: Specific area where the substrate binds.
• Types of Enzymes:
  • Exoenzymes: Produced inside and function outside the cell.
  • Endoenzymes: Produced inside and function within the cell.

Enzyme Activity Influences

• Factors:
  • Temperature: Affect reaction rate; high temperature can denature enzymes.
  • pH: Optimal pH required for enzyme function.
  • Substrate Concentration: High concentration can saturate enzyme activity.

Enzyme Inhibition

Competitive Inhibition

• Mechanism: Inhibitor competes with substrate for active site.
• Challenge: Inhibitor must have a higher affinity for binding than the substrate.

Non-Competitive Inhibition

• Mechanism: Inhibitor binds to allosteric site, altering active site shape.

Feedback Inhibition

• Process: End product of a reaction inhibits the pathway to prevent overproduction.
• Example: Metabolic pathways in bacterial cells.

Conclusion

• Review the concepts of enzyme inhibition and metabolic reactions for better understanding.
• Prepare for the next lecture on cellular respiration.