Chapter 5: Active Transport and Bulk Transport

Active Transport

• Definition: Movement of molecules against the concentration gradient (low to high concentration) which requires energy.
  • Opposite of passive transport.
  • Always involves a protein transporter.
  • Requires energy, unlike passive transport.

Types of Active Transport

1. Primary Active Transport

   • Direct use of ATP for energy.
   • Example: Sodium-Potassium Pump (Na+/K+ ATPase)
     • Moves 3 Na+ out and 2 K+ into the cell.
     • Creates a net negative charge inside the cell (electrogenic pump).

2. Secondary Active Transport

   • Does not use ATP directly.
   • Relies on the electrochemical gradient created by primary active transport.
   • Example: Sodium-Glucose Transporter
     • Sodium moves down its gradient (releases energy).
     • Glucose moves against its gradient (uses the energy released by sodium).

Electrochemical Gradients

• Definition: Combination of concentration gradients and electrical gradients across a cell membrane.
• Essential for various cellular processes.

Bulk Transport

• Definition: Movement of large molecules or large quantities of molecules via vesicles.
  • Requires energy (active transport).

Types of Bulk Transport

1. Endocytosis: Import of materials into the cell.

   • Phagocytosis: "Cell eating," intake of large particles or cells.
   • Pinocytosis: "Cell drinking," intake of solutes and fluids.
   • Receptor-Mediated Endocytosis: Specific molecules bind to receptors before intake.
     • Example: Familial hypercholesterolemia due to defective LDL receptors.

2. Exocytosis: Export of materials out of the cell.

   • Vesicles fuse with the plasma membrane to release contents outside the cell.

Key Concepts

• Carrier Proteins: Essential for active transport.
  • Types: Uniporters (one molecule), Symporters (two different molecules, same direction), Antiporters (two different molecules, opposite directions).
• Membrane Potential: Created by the imbalance of ion charges across the membrane due to active transport.

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• Chapter 6: Focus on metabolism, energy, and enzymes.