25. Coated vesicles

coated vesicles

Coated vesicles are small, membrane-bound structures (20-250 nm in diameter) involved in transporting proteins, lipids, and other secretory products between cellular compartments. They are characterized by a coating of specific proteins that help in vesicle formation and targeting.

types

• Clathrin-Coated Vesicles:

  • Involved in receptor-mediated endocytosis, a process by which cells internalize molecules such as hormones, nutrients, and proteins from the extracellular environment.

  • These vesicles are coated with clathrin, a protein that forms a triskelion shape composed of three clathrin heavy chains and three light chains.

  • Clathrin-coated vesicles are formed from regions of the plasma membrane called coated pits, which are specialized areas enriched with receptors and clathrin.

  • They also form at the trans-Golgi network to transport proteins to lysosomes or to the cell surface.

• COPI- and COPII-Coated Vesicles (Coatomer-Coated Vesicles):

  • These vesicles are coated with coatomer proteins (COPs) and are involved in transport within the secretory pathway.

  • COPII-Coated Vesicles:

    • Responsible for anterograde transport—from the endoplasmic reticulum (ER) to the Golgi apparatus.

    • Mediate the transport of newly synthesized proteins and lipids from the ER to the Golgi.

  • COPI-Coated Vesicles:

    • Responsible for retrograde transport—from the Golgi back to the ER.

    • Involved in intra-Golgi transport, moving vesicles between the Golgi cisternae.

    • Help in recycling ER-resident proteins and lipids back to the ER.

• Caveolae:

  • Small (50-100 nm) flask-shaped invaginations of the plasma membrane.

  • Rich in cholesterol and sphingolipids and are abundant in endothelial cells, where they are involved in the exchange of metabolites between cells and the bloodstream.

  • Play a role in potocytosis, a form of receptor-mediated endocytosis distinct from clathrin-mediated endocytosis.

  • Contain proteins called caveolins (integral membrane proteins) and cavins (peripheral membrane proteins) that are essential for their formation and function.

  • Involved in signal transduction, lipid regulation, and cellular trafficking.

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