What does cytosol mean?
The cytosol is the watery, semi-fluid substance that fills the interior of a biological cell and forms part of its cytoplasm. It is the medium in which the cell's organelles — the mitochondria, ribosomes, and other specialised structures — are suspended, and it is itself far more than inert liquid: dissolved salts, sugars, amino acids, proteins, and enzymes crowd this environment, and many essential metabolic reactions, including glycolysis, occur directly within it. In everyday scientific writing, the term appears chiefly in biology, biochemistry, and medical contexts, as in phrases like 'the cytosol of the cell' or 'released into the cytosol'. It should not be confused with cytoplasm, the broader term covering everything inside the cell membrane except the nucleus; the cytosol is specifically the fluid component of that material. Understanding the distinction gives precision when describing how substances move through, or react within, the living cell.
nounThe aqueous component of the cytoplasm of a cell, in which the organelles are suspended and in which many metabolic reactions take place.
- The fluid, aqueous portion of the cytoplasm in which a cell's organelles are suspended and in which many metabolic reactions occur.
"Glycolysis takes place entirely within the cytosol of the cell."
"The enzyme remains dissolved in the cytosol until it is needed."
"Ions such as calcium can be released rapidly from storage compartments into the cytosol."
Rarely pluralised; typically discussed in relation to a specific cell type, e.g. comparing the cytosol of one cell with another.
"Researchers compared the protein composition of the two cytosols."
The cytosol isn't empty filler — it's a crowded, gel-like soup where thousands of chemical reactions happen at once, all packed into roughly two-thirds of a typical cell's volume.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of cytosol
Cytosol derives from the Greek-derived combining form 'cyto-', meaning 'cell' (from Greek 'kytos', meaning a hollow vessel or container), combined with 'sol' from 'solution'. The word was coined in the twentieth century by cell biologists who needed a precise term for the soluble, fluid fraction of the cytoplasm. It belongs to the same word family as other 'cyto-' terms such as cytoplasm, cytology, and cytokinesis, which together reflect the vocabulary built on the Greek root during the development of modern cell biology.
Related word forms
How cytosol is actually used
A technical term used almost exclusively in biology, biochemistry, and medicine; it is rare in general prose. It refers specifically to the fluid phase of the cytoplasm, excluding organelles, and is often encountered in discussions of metabolism, signalling, and protein synthesis.
Easily confused with cytosol
Cytoplasm is everything inside the cell membrane excluding the nucleus, whereas the cytosol is only the fluid portion of that material in which the organelles are suspended.