The cytosol, also known as cytoplasmic matrix or groundplasm,[2] is one of the liquids found inside cells (intracellular fluid (ICF)).

The cytosol also contains large amounts of macromolecules, which can alter how molecules behave, through macromolecular crowding.

The term "cytosol" was first introduced in 1965 by H. A. Lardy, and initially referred to the liquid that was produced by breaking cells apart and pelleting all the insoluble components by ultracentrifugation.

[5] This water of solvation is not active in osmosis and may have different solvent properties, so that some dissolved molecules are excluded, while others become concentrated.

The loss of sodium and chloride ions compensates for the osmotic effect of the higher concentration of organic molecules inside the cell.

[27] Some of these molecules can allow cells to survive being completely dried out and allow an organism to enter a state of suspended animation called cryptobiosis.

[28] In this state the cytosol and osmoprotectants become a glass-like solid that helps stabilize proteins and cell membranes from the damaging effects of desiccation.

These cells were also able to synthesize proteins if given ATP and amino acids, implying that many of the enzymes in cytosol are bound to the cytoskeleton.

[35] This is an irregular mass of DNA and associated proteins that control the transcription and replication of the bacterial chromosome and plasmids.

In eukaryotes the genome is held within the cell nucleus, which is separated from the cytosol by nuclear pores that block the free diffusion of any molecule larger than about 10 nanometres in diameter.

[39] These are about 2 micrometres in diameter and last for only a few milliseconds, although several sparks can merge to form larger gradients, called "calcium waves".

[40] Concentration gradients of other small molecules, such as oxygen and adenosine triphosphate may be produced in cells around clusters of mitochondria, although these are less well understood.

[44] Channeling can make a pathway more rapid and efficient than it would be if the enzymes were randomly distributed in the cytosol, and can also prevent the release of unstable reaction intermediates.

[52] Non-membrane bound organelles can form as biomolecular condensates, which arise by clustering, oligomerisation, or polymerisation of macromolecules to drive colloidal phase separation of the cytoplasm or nucleus.

Although the cytoskeleton is not part of the cytosol, the presence of this network of filaments restricts the diffusion of large particles in the cell.

For example, in several studies tracer particles larger than about 25 nanometres (about the size of a ribosome)[53] were excluded from parts of the cytosol around the edges of the cell and next to the nucleus.

These microdomains could influence the distribution of large structures such as ribosomes and organelles within the cytosol by excluding them from some areas and concentrating them in others.

[60][61] Molecules taken into the cell by endocytosis or on their way to be secreted can also be transported through the cytosol inside vesicles,[62] which are small spheres of lipids that are moved along the cytoskeleton by motor proteins.

[66] The localization of pathways can be different in other organisms, for instance fatty acid synthesis occurs in chloroplasts in plants[67][68] and in apicoplasts in apicomplexa.