The exposed free surface of a polarized epithelial cell.
autophagosome
A vesicle containing internal organelles enclosed by fragments of cytoplasmic membranes that fuses with lysosomes.
autophagy
The degradation of cytoplasmic proteins and organelles by their enclosure in cytoplasmic vesicles that fuse with lysosomes.
basolateral domain
The surface region of a polarized epithelial cell that is in contact with adjacent cells or the extracellular matrix.
cis-Golgi network
The region of the Golgi apparatus at which proteins enter from the endoplasmic reticulum.
clathrin
A protein that coats the cytoplasmic surface of cell membranes and assembles into basketlike lattices that drive vesicle budding.
clathrin-coated vesicle
A transport vesicle coated with clathrin.
COP-coated vesicle
Transport vesicles coated with COP I or COP II.
COPI and COPII
The two proteins other than clathrin that coat transport vesicles (COP indicates coat protein).
endocytosis
The uptake of extracellular material in vesicles formed from the plasma membrane.
endoplasmic reticulum (ER)
An extensive network of membrane-enclosed tubules and sacs involved in protein sorting and processing as well as in lipid synthesis.
endosome
A vesicular compartment involved in the sorting and transport to lysosomes of material taken up by endocytosis.
exocyst
A protein complex on the plasma membrane at which exocytosis occurs.
flippase
A protein that catalyzes the translocation of lipids across the membrane of the endoplasmic reticulum.
glycosidase
An enzyme that removes sugar residues from its substrate.
glycosylphosphatidylinositol (GPI) anchor
A glycolipid containing phosphatidylinositol that anchors proteins to the external face of the plasma membrane.
glycosyltransferase
An enzyme that adds sugar residues to its substrate.
Golgi apparatus
A cytoplasmic organelle involved in the processing and sorting of proteins and lipids. In plant cells, it is also the site of the synthesis of cell wall polysaccharides.
Golgi complex
See Golgi apparatus.
Golgi stack
The compartments of the Golgi apparatus within which most metabolic activities take place.
lysosomal storage disease
A family of diseases characterized by the accumulation of undegraded material in the lysosomes of affected individuals.
lysosome
A cytoplasmic organelle containing enzymes that break down biological polymers.
mannose-6-phosphate
A modified mannose residue that targets proteins to lysosomes.
microsome
A small vesicle formed from the endoplasmic reticulum when cells are disrupted.
phagocytosis
The uptake of large particles, such as bacteria, by a cell.
phagolysosome
A lysosome that has fused with a phagosome or autophagosome.
phagosome
A vacuole containing a particle taken up by phagocytosis.
protein disulfide isomerase
An enzyme that catalyzes the formation and breakage of disulfide (S–S) linkages.
Rab
A family of small GTP-binding proteins that play key roles in vesicular transport.
rough endoplasmic reticulum (ER)
The region of the endoplasmic reticulum covered with ribosomes and involved in protein metabolism.
secretory pathway
The movement of secreted proteins from the endoplasmic reticulum to the Golgi apparatus and then, within secretory vesicles, to the cell surface.
secretory vesicle
A membrane-enclosed sac that transports proteins from the Golgi apparatus to the cell surface.
signal patch
A recognition determinant formed by the three-dimensional folding of a polypeptide chain.
signal peptidase
An enzyme that removes the signal sequence of a polypeptide chain by proteolysis.
signal recognition particle (SRP)
A particle composed of proteins and srpRNA that binds to signal sequences and targets polypeptide chains to the endoplasmic reticulum.
signal sequence
A hydrophobic sequence at the amino terminus of a polypeptide chain that targets it for secretion in bacteria or incorporation into the endoplasmic reticulum in eukaryotic cells.
smooth endoplasmic reticulum
The major site of lipid synthesis in eukaryotic cells.
SNARE
A transmembrane protein that mediates fusion of vesicle and target membranes.
SRP receptor
A protein on the membrane of the endoplasmic reticulum that binds the signal recognition particle (SRP).
SRP RNA
The small cytoplasmic RNA component of SRP.
synaptic vesicle
A secretory vesicle that releases neurotransmitters at a synapse.
trans Golgi network
The Golgi compartment within which proteins are sorted and packaged to exit the Golgi apparatus.
transitional ER
The region of the ER from which proteins exit for the Golgi apparatus.
translocon
The membrane channel through which polypeptide chains are transported into the endoplasmic reticulum.
unfolded protein response
A cellular stress response in which an excess of unfolded proteins in the endoplasmic reticulum leads to general inhibition of protein synthesis, increased expression of chaperones, and increased proteasome activity.
vacuole
A large membrane-enclosed sac in the cytoplasm of eukaryotic cells. In plant cells, vacuoles function to store nutrients and waste products, to degrade macromolecules, and to maintain turgor pressure.
