noun, plural: organelles
Organelle literally means "little organs". As the body is composed of various organs, the cell, too, has "little organs" that perform special functions. They are membrane-bound compartments or structures of a cell. A eukaryotic cell contains many organelles, for example, the nucleus, endoplasmic reticulum, golgi apparatus, mitochondria, and chloroplast (plastid). However, not all these organelles are found in only one cell or in an organism. The chloroplast, for instance, is abundant in plant cells but not in animal cells. Prokaryotes, which were believed to have no organelles, have been recently described to possess “organelles”. Examples are carboxysome (a protein-shell compartment for carbon fixation in some bacteria), chlorosome (a light harvesting complex in green sulfur bacteria), magnetosome (found in magnetotactic bacteria), and thylakoid (in some cyanobacteria).
There are organelles that have their own DNA apart from the nucleus and are suggested to have originated from endosymbiotic bacteria according to the endosymbiotic theory. These organelles are mitochondria and plastids. The stricter definition of organelle does not include biomolecular complexes such as ribosomes and nucleosomes because they are not bounded by membranes. A more restrictive definition of organelle does not consider single-membrane bounded cytoplasmic structures, such as lysosomes.
Word origin: New Latin organella, diminutive of Medieval Latin organum, organ of the body, from Latin, implement, tool
- organellar (adjective)