Endocytosis
Endocytosis
Endocytosis (pronounced: en-doh-sy-TOH-sis) is a biological process in which a cell absorbs molecules, such as proteins, from outside the cell by engulfing them with its cell membrane. It is a form of active transport that moves particles, such as large molecules, parts of cells, and even whole cells, into a cell.
Etymology
The term "endocytosis" is derived from the Greek words "endo," meaning within, and "kytos," meaning cell. The term was first used in the late 19th century to describe the process by which cells internalize external materials.
Process
Endocytosis begins when the substance to be transported binds to the cell membrane. The cell membrane then invaginates, forming a pocket around the substance. The pocket pinches off, resulting in the substance being contained in a newly formed intracellular vesicle formed from the cell membrane.
There are three types of endocytosis: Phagocytosis, Pinocytosis, and Receptor-mediated endocytosis.
- Phagocytosis ("cell eating") is the process by which cells engulf large particles, such as bacteria or dead cells, forming a large vesicle known as a phagosome.
- Pinocytosis ("cell drinking") involves the engulfment of small particles or liquids, forming smaller vesicles.
- Receptor-mediated endocytosis is a more specific process where cells absorb metabolites, hormones, proteins – and in some cases viruses – by the inward budding of the plasma membrane. These substances bind to specific receptors on the cell surface before being engulfed.
Related Terms
- Exocytosis: The process by which a cell transports secretory products through the cytoplasm to the plasma membrane. Secretory products are packaged into transport vesicles (membrane-bound spheres).
- Vesicle: A small structure within a cell, consisting of fluid enclosed by a lipid bilayer.
- Cell membrane: The semipermeable membrane surrounding the cytoplasm of a cell.
- Active transport: The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.
External links
- Medical encyclopedia article on Endocytosis
- Wikipedia's article - Endocytosis
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