Lysosome

An organelle (a little organ) within a cell containing enzymes that degrade macromolecules (large molecules) and other materials (such as bacteria) taken up by a cell during the process of endocytosis. In endocytosis, macromolecules and particles outside the cell are taken up by the cell via a progressive invagination (inpouching) and eventual pinching off of a region of the cell membrane, forming a membrane-bound vesicle (bubble) within the cytoplasm of the cell. The vesicle then fuses with the lysosome and the lysosomal enzymes carry out their appointed task of destruction (by hydrolysis). Quite amazingly, the lysosomal enzymes do not normally damage the cell itself.

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A cytoplasmic membrane-bound vesicle measuring 5-8 nm (primary l.) and containing a wide variety of glycoprotein hydrolytic enzymes active at an acid pH; serves to digest exogenous material, such as bacteria, as well as effete organelles of the cells. [lyso- + G. soma, body]

- definitive lysosomes SYN: secondary lysosomes.

- primary lysosomes lysosomes produced at the Golgi apparatus where hydrolytic enzymes are incorporated; they fuse with phagosomes or pinosomes to become secondary lysosomes.

- secondary lysosomes lysosomes in which lysis takes place, owing to the activity of hydrolytic enzymes; they are believed to eventually become residual bodies. SYN: definitive lysosomes, digestive vacuole.

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ly·so·some 'lī-sə-.sōm n a saclike cellular organelle that contains various hydrolytic enzymes

ly·so·som·al .lī-sə-'sō-məl adj

ly·so·som·al·ly -mə-lē adv

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n.

a particle in the cytoplasm of cells that contains enzymes responsible for breaking down substances in the cell and is bounded by a single membrane. Lysosomes are especially abundant in liver and kidney cells. Foreign particles (e.g. bacteria) taken into the cell are broken down by the enzymes of the lysosomes. When the cell dies, these enzymes are released to break down the cell's components.

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ly·so·some (liґso-sōm) [lyso- + -some] a membrane-bound cytoplasmic organelle, generally 250–750 nm in diameter, containing hydrolytic enzymes in an acidic environment and involved in intracellular digestion. Lysosomal enzyme defects result in the progressive accumulation of undigested products within the cell, which leads to lysosomal storage disease (q.v.). See Plate 11. lysosomal adj