The cytosol is a semi-fluid matrix that fills the space between the plasma membrane and the nuclear membrane, and embedding various organelles and cellular substructures. Rather than being a uniform liquid, the cytosol is a highly complex and crowded solution of water-soluble ions, small molecules and macromolecules, organized into concentration gradients, complexes and cytoplasmic bodies. The cytosol provides structural support to the cell and the organelles. It is also the site for many cellular processes, including a large portion of the metabolic pathways, protein biosynthesis, intracellular transport and signal transduction.
The cytosol extends from the plasma membrane to the nuclear membrane. Staining patterns of the cytosol vary from smooth to granular, and the staining is often stronger close to the nucleus. In cell types with a flat morphology, it can be difficult to distinguish a staining of the cytosol from a staining of the plasma membrane.
Read more about the proteome of the cytosol.