Membrane Transport

Endocytosis

Phagocytosis

  • Taking in of solid substances by invagination of the cell surface membrane (eg. amoeba taking in food particles)
  • Sequence of events

1. A small portion of the cell surface membrane invaginates to enclose the solid particles.

2. The particle is packaged within a membrane-enclosed sac that can be large enough to be called a vacuole.

3. Phagocytic vacuole pinches off from the cell surface membrane.

4. Cell surface membrane reforms

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Pinocytosis

  • Taking in of liquid and soluble materials by invagination of the cell surface membrane

  • Sequence

1. A small portion of the cell surface membrane invaginates to enclose the liquid and soluble materials

2. The particle is packaged within a membrane-enclosed sac called pinocytotic vesicle.

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Receptor-mediated endocytosis

  • Taking in of specific substances irregardless of the low concentration in the extracellular fluid
  • Sequence
  1. When the specific substances also known as ligands bind to the receptor sites of receptor proteins they trigger the invagination of the cell surface membrane.
  2. This results in the formation of coated vesicle that contain specific ligand molecules
  3. After the ligands are taken up by the cell, the receptors are brought back to the cell surface membrane by the same vesicle.

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