Lysosomes are organelles in animal cells that digest macromolecules. Lysosomes are spherical vesicles that contain hydrolytic enzymes that can break down many types of biomolecules, including proteins, lipids, and nucleic acids. The lysosome’s membrane protects the cell from the digestive enzymes within it. Lysosomes were first described in 1955 by Christian de Duve and they were named after the Greek word for “digestion”, lysis.
The primary function of a lysosome is to degrade and recycle cellular waste material and damaged or unnecessary cell parts. When acellular material is engulfed by endocytosis or phagocytosis, it is delivered to a lysosome where it is degraded into small molecules that can be recycled for use in other cellular processes. In addition to their role in recycling, lysosomes also participate in programmed cell death (PCD), a process whereby a cell self-destructs when it is no longer needed or when it has been damaged beyond repair.
Lysosomal enzymes are classified according to their substrate specificity. For example, acid hydrolases cleave ester bonds in substrates such as fats and lipids; nucleases degrade DNA and RNA; glycosidases release monomers from oligo- and polysaccharides; sulfatases remove sulfate groups; phosphatases dephosphorylate phosphorylated compounds; etc. There are over 60 different kinds of known lysosomal enzymes. Most of these enzymes are synthesized in the rough endoplasmic reticulum (ER) and then transported to the Golgi apparatus for further modification before being delivered to lyso