Lysosomes

ID #1964

How do lysosomes degrade other proteins that don't come from endocytosis or do they? It seems like only vesicles budding from the plasma membrane fuse with the early endosome, so I wonder how other molecules in the cell get degraded not including entire organelles which I know get degraded by autophagy and also not including cytosolic proteins. Also, are nucleases, proteases, lipases, etc. in the lysosome to do work or to be degraded? Are acid hydrolases the only enzymes doing the work or are nucleases, proteases, etc. doing work too along with acid hydrolases?


First, it's important to realize that the nucleases, proteases, etc. that get sent to the late endosome to work in a lysosome ARE the acid hydrolases. The "hydrolase" part just means they hydrolyze covalent linkages between monomers in a macromolecule, and the "acid" part indicates that they are optimally active at an acidic pH.

 

Since lysosomes have "bigger" things to worry about degrading, like entire bacteria or organelles, they don't need to be "bothered" with things like individual proteins that fold wrong or become inactive. So the cell has an entirely different method of removing and degrading those that doesn't use a lysosome. There are special protein-degrading "machines" in cells called proteasomes which do this work.

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