Crossing membranes - active processes (Active transport).

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  • Created by: Steff06
  • Created on: 06-04-16 10:28
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  • Crossing membranes - ACTIVE processes
    • Sometimes cells may need to move material into or out of a cell more quickly than simple diffusion allows.
    • Active transport: Movement of molecules or ions across membrane, which uses ATP to drive protein pumps within the membrane.
    • Active transport protein pumps:
      • Carry specific molecules ONE WAY across the membrane. Carrying molecules across the membrane, use metabolic energy in the form of ATP.
      • Carry molecule in OPPOSITE direction to the conc gradient. Carry them at a much FASTER rate than by diffusion. Molecules ACCUMULATED inside cells or outside.
      • AGAINST a conc gradient via CARRIER PROTEINS.
    • Ensuring 1 way flow: Energy pumping molecules across membranes by active transport changes the SHAPE of the carrier protein. Means the specific molecule fits into the CARRIER protein on one side only.
    • Ca+ ion movement in muscles: Muscle fibres only CONTRACT if calcium is present. When muscles are stimulated to contract, calcium ions are released. When muscles need to RELAX, Ca+ ions pumped back into stores by Ca+ ion pumps.
    • BULK transport: ENDOCYTOSIS = Bringing materials INTO the cell. EXOCYTOSIS = moving materials OUT OF the cell.
      • Examples = HORMONES e.g. insulin. Plant cells e.g. materials to build cell wall. White blood cells (engulf microorganisms by forming vesicles).
    • Bulk transport requires energy from ATP used to move membranes around to form the VESICLES needed and to move these around the cell.


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