= Lysosome
{wiki}
A <lysosome> is an acidic digestive and recycling <organelle>: one surrounding <lipid bilayer> encloses a <lysosomal lumen> containing <acid hydrolases>. These <enzymes> break down <proteins>, <nucleic acids>, <carbohydrates> and <lipids> by <hydrolysis>. Cargo can originate outside the <biological cell>, entering through <endocytosis>, or within its own <cytoplasm>, delivered through <autophagy>. Digestion therefore serves both disposal and reuse.<The Cell: A Molecular Approach, 2nd edition by Geoffrey M. Cooper/Lysosomes>[The Cell: A Molecular Approach, 2nd edition by Geoffrey M. Cooper; Cooper, The Cell, 2nd edition (2000), Lysosomes: opening paragraph; Lysosomal Acid Hydrolases; Phagocytosis and Autophagy, Figure 9.37]{ref}
\Image[/lysosome-compartment-and-cargo-routes.png]
{title=<Lysosome> compartment, cargo delivery and recycling}
{description=Original schematic: <endocytosis> and <macroautophagy> supply material for digestion, while <secretory protein routing> supplies digestive <enzymes>. The enclosure at the right distinguishes <lysosomal lumen> from <cytosol>; arrows indicate routes, not measured rates. Shapes, sizes and cargo counts are illustrative.}
An <endosome> sorts endocytosed cargo: some returns to the <cell membrane>, while some proceeds toward <lysosomes>. An <autophagosome> instead encloses material already in the <cytoplasm>. Both routes bring cargo into contact with digestive <enzymes>; neither implies that every internalized <molecule> is destroyed.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others/Transport from the Trans Golgi Network to Lysosomes>[Alberts and others, Molecular Biology of the Cell, 4th edition (2002), Multiple Pathways Deliver Materials to Lysosomes, Figure 13-35]{ref}
Enzyme supply is a different itinerary from cargo disposal. <Secretory protein routing> and <protein targeting> deliver newly made digestive <enzymes> through the <endoplasmic reticulum>, <Golgi apparatus> and <trans-Golgi network> toward <lysosomes>.<The Cell: A Molecular Approach, 2nd edition by Geoffrey M. Cooper/The Golgi Apparatus>[The Cell: A Molecular Approach, 2nd edition by Geoffrey M. Cooper; Protein Sorting and Export from the Golgi Apparatus, lysosomal enzyme targeting]{ref} The existing <membrane transport> and <differential centrifugation> articles explain the boundary-crossing and separation principles used below.
A <proteasome> is a different digestive machine: a <protein> complex without a surrounding <lipid bilayer>, acting on individual <proteins> in the <cytosol> and <cell nucleus>. Many targets carry <ubiquitin> chains. A <lysosome> accepts a much broader range of cargo, including material delivered inside an <autophagosome>. Thus an unwanted soluble <protein> and an unwanted <mitochondrion> pose different disposal problems; a <proteasome> does not swallow an intact <mitochondrion>.<The Cell: A Molecular Approach, 2nd edition by Geoffrey M. Cooper/Protein Degradation>[The Cell: A Molecular Approach, 2nd edition by Geoffrey M. Cooper; Cooper, The Cell, 2nd edition (2000), The Ubiquitin-Proteasome Pathway, Figure 7.39; Lysosomal Proteolysis, Figure 7.41]{ref}
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