Cytosol is the fluid portion of a cell's cytoplasm, which lies outside the organelles and other insoluble components of the cytoplasm. Cytosol contains water, free proteins, and a variety of other substances; yet, far from being a complex biochemical broth, it is actually highly organized at the molecular level. Most importantly, it is where a major part of cellular metabolism takes place. The proteins within cytosol play an important role in glycolysis, serve as intracellular receptors, and form part of ribosomes, enabling protein synthesis. Cytosol also contains the cytoskeleton.


In prokaryotes, all chemical reactions take place in the cytosol. In eukaryotes, the cytosol forms the surrounding environment of organelles. In plants, the amount of cytosol can be reduced due to the large tonoplast (central vacuole) that takes up most of the cell interior volume.