Membrane transport

Membrane Transport

  • Main Categories:

    • Carrier-mediated (requires protein carrier)

    • Non-carrier-mediated (no carrier protein)

  • Energetics:

    • Passive processes: No ATP; molecules move down gradient (e.g., Simple Diffusion, Osmosis, Facilitated Diffusion).

    • Active processes: Requires ATP; molecules move against gradient (e.g., Active Transport, Bulk Transport).

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  • Key terms: Carrier (protein aiding transport), Channel (pore for ions/water), Aquaporins (water channels).

Non-Carrier Mediated Transport

  • Simple Diffusion (passive): Movement from high to low concentration for small, nonpolar, lipid-soluble molecules

  • Osmosis (passive): Diffusion of water across a membrane through aquaporins (water channels). Both are driven by kinetic energy.

Carrier-Mediated Transport (Na+/K +) 3 Na+ out 2K+ in

  • Requires a membrane carrier protein.

  • Facilitated Diffusion (passive): Carrier assists movement down the concentration gradient; no ATP needed (e.g., glucose, amino acids).

  • Active Transport (active): Carrier moves substrates against the concentration gradient; requires ATP..

Bulk Transport

  • Moves large amounts of material by deforming the cell membrane, forming vesicles.

  • Endocytosis (inward): Engulfs material (e.g., bacteria, proteins, antibodies) into the cell; energy-requiring.

  • Exocytosis (outward): Vesicles fuse with the plasma membrane to release contents (e.g., mucus, hormones, neurotransmitters) outside the cell; energy-requiring.

  • Energy-dependent, no carrier proteins.