organell

Organell, sometimes spelled organelle, is a term in cell biology for a specialized subunit within a cell that performs a specific function. Most organelles are enclosed by a phospholipid membrane that separates their interior from the cytosol, enabling compartmentalized metabolism. In eukaryotic cells, organelles organize complex processes in defined spaces; prokaryotic cells generally lack membrane-bound organelles, although they possess various functional structures.

Common organelles include the nucleus, which houses genetic material and coordinates gene expression; mitochondria, the sites of ATP production through oxidative phosphorylation and respiration; chloroplasts, found in plants and algae, where photosynthesis occurs; the endoplasmic reticulum (rough and smooth), which synthesizes proteins and lipids; the Golgi apparatus, which modifies, sorts, and ships cellular products; lysosomes and peroxisomes, which break down macromolecules and detoxify; vacuoles, which store water and other substances; and various vesicles that transport cargo between compartments. Ribosomes, though not membrane-bound, are essential organelles responsible for protein synthesis and occur free in the cytosol or attached to the endoplasmic reticulum.

Most membrane-bound organelles are thought to have originated, in part, through endosymbiotic events, notably mitochondria and, in plants and algae, chloroplasts, which contain their own DNA and ribosomes resembling those of prokaryotes.

Organelles are central to cell biology and physiology. Defects in organelle function can underlie a range of diseases, including lysosomal storage disorders, mitochondrial diseases, and disorders of vesicular trafficking. Modern imaging and molecular techniques continue to reveal the diversity and dynamics of organellar compartments.