Figure 221

Three autophagic pathways for degradation of cytoplasmic constituents. In macroautopbagy, a portion of the cytoplasm or an entire organelle is surrounded by an intracellular membrane of the endoplasmic reticulum to form an autophagosome vacuole. After fusion with a lysosome, the contents of the vacuole are degraded. In microautopbagy, cytoplasmic proteins are internalized into lysosomes by invagination of the lysosomal membrane. Chaperone-mediated direct transport to lysosomes is the most selective process for degradation of specific cytoplasmic proteins. It requires assistance of proteins called chaperones. Chaperones bind to the protein and help transport it into the lysosomal lumen, where it is finally degraded.

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