Lesson 20: Endocytosis and Exocytosis Key Terms

endocytosis

uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membrane-enclosed organelle

endocytic vesicle

vesicle formed as material ingested by the cell during endocytosis is enclosed by a small portion of the plasma membrane, which first invaginates and the pinches off to form the vesicle

endosome

membrane-bound sorting organelle that processes and routes molecules moving between the cell membrane, Golgi apparatus, and lysosomes

pinocytosis

“cell drinking”, soluble materials are continually taken up from environment in small vesicles and moved into endosomes along with the membrane-bound molecules

caveolae

invaginations at the cell surface that bud off internally to form pinocytic vesicles, thought to form lipid rafts, regions of membrane rich in certain lipids

caveolins

family of unusual integral membrane proteins that are the major structural proteins in caveolae

macropinocytosis

clathrin-independent, dedicated degradative endocytic pathway induced in most cell types by cell-surface receptor activation by specific cargoes

receptor-mediated endocytosis

internalization of receptor-ligand complexes from the plasma membrane by endocytosis, a type of receptor-down regulation

low-density lipoproteins (LDLs)

large complex composed of a single protein molecule and many esterified cholesterol molecules, together with other lipids

transferrin receptor

cell-surface receptor for transferrin; delivers iron to the cell interior via receptor-mediated endocytosis and recycling of receptor transferrin complex

early endosomes

common receiving compartment with which most endocytic vesicles fuse and where internalized cargo is sorted either for return to the plasma membrane or for degradation by inclusion in a late endosome

late endosomes

compartment formed from a bulbous, vacuolar portion of early endosomes by a process called endosome maturation; fuse with one another and with lysosomes to form endolysosomes that degrade their contents

multivesicular bodies

intermediates in the endosome maturation process; early endosomes that are on their way to becoming late endosomes

transcytosis

uptake of material at one face of a cell by endocytosis, its transfer across a cell in vesicles, and discharge from another face by exocytosis

recycling endosome

organelle that provides an intermediate state on the passage of recycled receptors back to the cell membrane, regulates plasma membrane insertion of some proteins

phagocytosis

process by which unwanted cells, debris, and other bulky particulate material is endocytosed by a cell

phagosome

large intracellular membrane-enclosed vesicle that is formed as a result of phagocytosis

exocytosis

excretion of material from the cell by vesicle fusion with the plasma membrane; can occur constitutively or be regulated

constitutive secretory pathway

pathway present in all cells by which molecules such as plasma membrane proteins are continually delivered to the plasma membrane from the Golgi apparatus in vesicles that fuse with the plasma membrane

regulated secretory pathway

secretory pathway found mainly in cells specialized for secreting products rapidly on demand in which soluble proteins and other substances are initially stored in secretory vesicles for later release

secretory vesicle

membrane-enclosed organelle in which molecules destined for secretion are stored prior to releases

synaptic vesicle

small neurotransmitter-filled secretory vesicle found at the axon terminals of nerve ells