Organelle
Organelle, any of the specialized structures within a cell that perform a specific function. Organelles may be surrounded by a membrane, seen mainly in eukaryotic organisms, or they may lack a membrane, which occurs in both prokaryotic and eukaryotic cells.
- Endoplasmic reticulum: involved in the synthesis, folding, modification, and transport of proteins.
- Golgi apparatus: responsible for transporting, modifying, and packaging proteins and lipids.
- Mitochondrion: generates large quantities of energy in the form of adenosine triphosphate (ATP).
- Lysosome: responsible for the digestion of macromolecules, old cell parts, and microorganisms.
- Peroxisome: involved in the oxidation of specific biomolecules and the biosynthesis of membrane lipids known as plasmalogens.
- Ribosome: serves as the site of protein synthesis.
Examples of membrane-bound organelles include the nucleus, mitochondria, lysosomes, peroxisomes, the endoplasmic reticulum, chloroplasts, and the Golgi apparatus. Examples of non-membrane bound organelles include centrosomes and ribosomes.
Organelles in unicellular organisms are the equivalent of organs in multicellular organisms. The contractile vacuole of protozoans, for example, extracts fluid wastes from the cell and eliminates them from the organism, as does the kidney in larger organisms.
See also list of 6 cell organelles.