Vesikkel

Vesikkel (vesicle) is a small, membrane-bound compartment that forms within cells or is released from them. Vesicles are bounded by a lipid bilayer and typically range from a few tens to a few hundreds of nanometers in diameter. They are essential for transporting, storing, and disposing of materials as part of the cell’s endomembrane system and intercellular communication.

Formation and structure are tightly coordinated. Vesicles bud from a donor membrane, with coat protein complexes shaping the vesicle and aiding membrane scission. Popular coat systems include COPII for endoplasmic reticulum to Golgi transport, COPI for Golgi-to-ER cycling, and clathrin for endocytosis and trans-Golgi network pathways. Vesicles carry specific cargo and display targeting signals that ensure they reach the correct compartment.

Common types include:

- Transport vesicles, which shuttle proteins and lipids between organelles (for example, ER to Golgi and Golgi to other destinations).

- Secretory vesicles, which store and release enzymes, hormones, or neurotransmitters by exocytosis.

- Endocytic vesicles, which internalize material from the plasma membrane and deliver it to endosomes or lysosomes.

- Lysosomes, a class of vesicles containing hydrolytic enzymes for macromolecule degradation.

- Synaptic vesicles, which store neurotransmitters in neurons.

- Exosomes and microvesicles, released into the extracellular space and involved in intercellular signaling.

- In plants, large vacuoles function as major vesicular compartments involved in storage and turgor regulation.

Vesicles carry lipids and proteins as part of their membrane and cargo. Docking and fusion are mediated by SNARE proteins and Rab GTPases, guiding vesicles to their correct destinations. Disruptions in vesicle trafficking are associated with various diseases, including neurological and metabolic disorders.