Unit 1 - 3.1 Vesicular Transport Notes

Membrane Transport Categories

  • Four Main Categories: Bulk flow; diffusion; protein-mediated transport; and vesicular transport.

Vesicular Transport

  • Purpose: For macromolecules too large for protein-mediated transport.

  • Energy Requirement: Requires ATP.

  • Methods: Endocytosis (internalize) and Exocytosis (release).

Endocytosis

  • Purpose: To internalize macromolecules.

  • Types:

    • Receptor-mediated endocytosis:

      • Highly selective; requires specific receptor for ligand.

      • Also known as clathrin-mediated endocytosis.

      • Example: LDL receptor-mediated endocytosis of cholesterol-rich LDL.

    • Phagocytosis:

      • Involves engulfing large solid particles (dead/damaged cells, bacteria, viruses).

      • Performed by phagocytes (macrophages, neutrophils).

      • Begins with particle binding to a non-specific plasma membrane receptor.

      • Forms pseudopods to enclose particles, creating a membrane-bound vesicle called a phagosome.

    • Pinocytosis (Bulk-phase endocytosis):

      • Non-selectively encloses extracellular fluid droplets.

      • No receptor proteins involved.

      • Vesicle fuses with a lysosome for digestion.

      • Common in absorptive cells of intestines and kidneys.

Exocytosis

  • Process: Cytoplasmic vesicles move to and fuse with the plasma membrane, releasing contents to the extracellular space.

  • Substances Released: Digestive enzymes, hormones, mucus, neurotransmitters.