BIOC 212 Lecture Notes - Lecture 10: Endosome, Endocytosis, Invagination
14 Oct 2015
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Receptor recycling ph 7. 4 ph 6. 0: extracellular ligands are bound by transmembrane pm receptors, transported to early endosome for sorting, ph of early endosome is lower than extracellular space, causing ligands to separate from receptors. Average charge on proteins change, interactions are weakened. Ldl: low density lipoprotein, cholesterol carrier: empty receptors are recycled back to pm, free ligands progress to lysosome. Endosome maturation: some tm proteins are marked for endocytosis by modification with mono-ubiquitin at pm. If ubiquitin is not removed, proteins are not recycled to pm: early endosomes mature into mvbs (multivesicular bodies) by invaginating and pinching-off membrane, mvb contents cannot be recycled to. Autophagy: large-scale digestion of cytosol and membranes, starting phagophore vesicle is extended around contents, lipids and peripheral membrane proteins added through cytosol, contents are enclosed in an autophagosome. Large range of sizes: autophagosome fuses with lysosome to digest contents. Selective autophagy: cargo receptors attach selected substrates to the phagophore, receptors for mono- and poly-ubiquitinated proteins.
