Indirect Active Transport

Indirect Active Transport

  • Involves moving two solutes simultaneously.
    • One solute moves along its concentration gradient.
    • The other solute moves against its concentration gradient.

Mechanism

  1. Initial Movement: A symport (or antiport) is used to move a solute against its concentration gradient by utilizing the movement of hydrogen ions along their concentration gradient.

    • High concentration of hydrogen ions outside the cell.
    • Solute particles are moved inside the cell against their concentration gradient.
    • The concentration gradient of hydrogen ions is used to facilitate this movement.

  2. Re-establishment of Gradient: To sustain the process, the hydrogen ion concentration gradient needs to be re-established using energy.

    • Hydrogen ions are moved back against their concentration gradient to maintain a high concentration outside the cell.

Key Aspects

  • Indirect Use of Energy: The solute is moved against its gradient without direct energy input, but energy is required to maintain the concentration gradient of the other ion (e.g., hydrogen).
  • Symport or Antiport: The mechanism can involve either a symport or an antiport.
    • The key is that one solute moves along its concentration gradient, dragging the other against its gradient.

Example: Sodium-Glucose Transporter

  • Glucose is moved into the cell against its concentration gradient by coupling it with the movement of sodium ions along their concentration gradient.
  • The sodium concentration gradient is then re-established by a sodium-potassium ATPase pump.
    • Sodium flows in, bringing glucose with it.

Important Considerations

  • The material covered depends on whether metabolism has been covered already.
    • If metabolism has been covered, this is the last chapter on the test.
    • If not, metabolism will also be included.