4.4 Endocytosis and Exocytosis

Clathrin

A cytosolic protein that binds to regions of the plasma membrane and helps initiate receptor-mediated endocytosis

Clathrin-Coated Pit

Aggregation of ligand-bound receptors on a cell membrane that pinches off and is internalized into the cell

Endocytosis

Process in which plasma membrane folds into the cell forming small pockets that pinch off to produce intracellular, membrane-bound vesicles

Exocytosis

Process in which intracellular vesicle fuses with plasma membrane, the vesicle opens, and its contents are liberated into the extracellular fluid

Fluid Endocytosis

Invagination of a plasma membrane by which a cell can engulf extracellular fluid

Phagocytosis

Engulfment of particles by a cell

Phagosomes

Plasma-membrane bound, intracellular sacs formed when a phagocyte engulfs a microbe

Pinocytosis

Endocytosis when the vesicle encloses extracellular fluid or specific molecules in the extracellular fluid that have bound to proteins on the extracellular surface of the plasma membrane

Receptor-Mediated Endocytosis

The specific uptake of ligands in the extracellular fluid by regions of the plasma membrane that invaginate and form intracellular vesicles

Receptors

Protein either on cell surface, in the cytosol, or in the nucleus that binds a chemical messenger such as a hormone or neurotransmitter and mediates its actions