ABSTRACT
Eukaryotic cells maintain a complex internal structure in the face
of continuous synthesis and turnover of endogenous constituents,
uptake of nutrients, and secretion of diverse products. Such dynamic
and interrelated activities require spatially separated compartments
containing distinct complements of proteins and lipids, which are
essential for their unique functions. Within compartments, many
components are organized in functional complexes and interface
with both cytoplasmica and exoplasmic spaces. Copies of most
membrane proteins have an identical topology, phospholipids are
selectively enriched in one leaflet of the bilayer, andmost glycolipids
Figure 3.1 Major trafficking pathways. Secretory pathway-rER: rough endoplasmic reticulum; ERGIC: ER/Golgi intermediate compartment; GA:
Golgi apparatus; TGN: trans-Golgi network; A: constitutive secretion
(vesicles and tubules); B: secretory vesicles formed by post-TGNmaturation;
ISG: immature secretory granule; C: secretory vesicles formed in the TGN;
MSG: mature secretory granule; APM: apical plasma membrane; LBPM:
lateral/basal plasmamembrane. Endocytic pathway-EE: early endosome; LE: late endosome; RE: recycling endosome; LY: lysosome; D: sorting of
lysosomal proteins to endosomes (single arrow); E: sorting of PM proteins
to LBPM (double arrow); LD: lipid droplet; N: nucleus; MT: microtubule.
