Autophagy

Autophagy is an adaptive survival response. Autophagy is the decomposition and recycling of redundant or dysfunctional cellular components by the lysosome. This ensures cellular survival during starvation by maintaining cellular energy levels and other 'nutrients' (for construction). Targeted components are isolated and transported by autophagosomes or vacuoles, which then fuse with the lysosome.

Lysosomes

Like the body, each cell contains specialised organs, called organelles. Lysosomes resemble the digestive system. Lysosomes (pH 4.8) contain weak bases with lipophilic properties and hydrolase enzymes (such as acid sphingomyelinase) that break down waste materials and cellular debris. The membrane keeps the enzymes inside. Autophagic vacuoles (trucks carrying waste) fuse with the lysosomes, which dispense their digestive enzymes into the vacuoles. Alternatively, material may cross the lysosomal barrier by the mediation of a chaperone complex (extremely selective, due to a membrane-bound protein receptor recognition system). Material from the cytoplasma may also directly engulf (by inward folding of the lysosomal membrane) into the lysosome (microautophagy). Lysosomes may process / digest remainders of dying cells or dysfunctional organelles, invading microbes / bacteria and cell surface receptor proteins. Lysosomes may also serve as a patch for when the plasma membrane is damaged, 'sealing' the wound. Lysosomes also produce proteins.