Lecture on Molecular Transport Mechanisms

Overview

• Prior topics discussed: diffusion, osmosis, active transport
• Current focus: Bulk transportation

Key Differences in Transport Mechanisms

• Diffusion & Osmosis
  • Move towards equilibrium
  • No energy input required
  • Movement described in relation to the gradient
  • Transports smaller molecules
• Active Transport
  • Moves against equilibrium
  • Requires energy input
  • Uses transport proteins
  • Transports smaller molecules
• Bulk Transport
  • Not based on gradient; based on into/out of cell
  • Used for larger molecules or many small molecules in bulk
  • Utilizes vesicles instead of transport proteins

Bulk Transportation

• Definition
  • Movement of large molecules or multiple small molecules collectively
  • Utilizes vesicles, membrane-bound sacs made up of phospholipid bilayers
  • Requires energy

Vesicles

• Little sacs that transport substances
• Membrane-bound, made of phospholipid bilayers

Types of Bulk Transport

• Endocytosis: Movement into the cell

  • Material approaches cell membrane, creates vesicle, moves into cell
  • Types:
    • Phagocytosis (cell eating): Involves large solid mass intake, e.g., white blood cell engulfing bacteria
    • Penocytosis (cell drinking): Intake of dissolved molecules in liquid
    • Receptor-Mediated Endocytosis: Specific intake via receptors
      • Lock and key mechanism for specific molecules
      • Efficient for sparse molecules

• Exocytosis: Movement out of the cell

  • Vesicle fuses with cell membrane, releases contents outside
  • Vesicle becomes part of the cell membrane

Summary

• Bulk transport moves either large molecules or groups of smaller molecules
• Endocytosis and exocytosis describe direction of movement
• Uses vesicles for transportation, which require energy input
• Receptor-mediated endocytosis allows specificity in intake

Note: This lecture provides foundational understanding of various transport mechanisms critical to cellular function and the movement of substances across cell membranes.