Basic structure and function of cells
8.e1
1
RETPaHC
Carrier vesicles in transit from the endoplasmic reticulum to the
Golgi apparatus (anterograde transport) are coated by coat protein
complex II (COPII), whereas COPI-containing vesicles function in the
retrograde transport route from the Golgi apparatus (reviewed in Spang
(2013)).
The membranes contain specific signal proteins that may allocate
them to microtubule-based transport pathways and allow them to dock
with appropriate targets elsewhere in the cell, e.g. the plasma mem-
brane in the case of secretory vesicles. Vesicle formation and budding
at the trans-Golgi network involves the addition of clathrin on their
external surface, to form coated pits.
Specialized cells of the immune system, called antigen-presenting
cells, degrade protein molecules, called antigens, transported by the
endocytic pathway for lysosomal breakdown, and expose their frag-
ments to the cell exterior to elicit an immune response mediated ini-
tially by helper T cells.