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3.4 Carrier-mediated and vesicular transport processes

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    • Uses specialized membrane proteins

    • Can be passive or active

    • May be used repeatedly

    • Can only bind to specific substrates

    Carrier-mediated transport

    • No energy required

    • Moves down the concentration gradient

    • Solutes are typically carried from an area of high concentration to an area of low concentration

    Passive Transport

    • The general movement of a substance from high to low concentration until the concentration gradient is eliminated.

    • A type of passive transportation

    Diffusion

    • A special type of diffusion involving water moving across a selectively permeable membrane towards the side with higher solute concentration

    • A type of passive transportation

    Osmosis

    • Requires energy (ATP)

    • Can move substances regardless of the concentration gradient (it is not dependent on a gradient)

    • Allows cells to import or export specific materials even when that means moving them from low to high concentration

    Active transport

    • Passive movement of a substance across a plasma membrane by protein carrier

    • First, the molecule to be transported binds to a receptor site on the carrier protein.

    • This process takes place without ever creating a continuous open channel between the cell's exterior and interior.

    Facilitated diffusion

  • The binding site on the carrier protein that recognizes and attaches to a specific molecule so it can be transported across the cell membrane.

    Receptor site

  • Carrier proteins in the cell membrane that actively transport ions across the plasma membrane using ATP

    Ion pumps

    • The carrier protein if one kind of ion is moved in one direction and the other is moved in the opposite direction

    • A major function that maintain cell homeostasis

    Exchange pump

    • Ion with high concentrations in extracellular fluids but low in the cytoplasm

    • Slowly diffuse into the cell

    Na + (Sodium ion)

    • Ion with low concentrations in extracellular fluids but high in the cytoplasm

    • Slowly diffuse out of the cell

    K+ (Potassium ion)

    • Materials move into or out of the cell in vesicles

    • Small membrane enclosed sacs that form at, or fuse with, the plasma membrane

    • Endocytosis

    • Exocytosis

    Vesicular transport

    • The movement of relatively large volumes of extracellular material into the cytoplasm by the formation of the membranous vesicle at the cell surface

    • Receptor-mediated endocytosis

    • Pinocytosis

    • Phagocytosis

    Endocytosis

    • Produces vesicles containing a specific target molecule in high concentrations

    • Begins when molecules in the extracellular fluid bind to the receptors on the plasma membrane surface

    • The receptor binds to a specific target molecules called ligands

    • Cluster together and pinches off = coated vesicle

    Receptor-mediated endocytosis

    • Cell drinking

    • The introduction of fluids into the cytoplasm by enclosing them in membranous vesicles at the cell surface

    Pinocytosis

    • Cell eating

    • The engulfing of extracellular materials or pathogens; movement of extracellular materials into the cytoplasm by enclosure in a membranous vesicle

    Phagocytosis

  • Temporary cytoplasmic extensions typical of mobile of phagocytic cells

    Pseudopodia

    • Reverse of endocytosis

    • The ejection of cytoplasmic materials by fusion of membranous vesicle with the cell membrane

    Exocytosis