The cytosol or cytoplasmic matrix is the fluid that is located inside the cells. It constitutes the majority of the intracellular fluid.

In eukaryotic cells, the cytosol is found within the cell membrane and is included in the cytoplasm, but it is not within the organelles or the nucleus.

In eukaryotic cells, the cytosol or hyaloplasm occupies most of the cell volume.

The cytosol is made up of between 70 and 75% water, the rest of its components forming a colloidal solution : protides  (amino acids, enzymes, structural proteins, etc.), lipids, carbohydrates  (polysaccharides, monosaccharides, etc.), nucleic acids  (nucleotides, nucleosides, tRNA, mRNA, ATP, etc.), products of metabolism and dissolved mineral salts.

The water content in the cytosol is variable, since it can show two states with different consistency: the gel state, of viscous consistency, and the sol state, of fluid consistency. The cell can change the state of the cytosol from sol to gel or vice versa, depending on the needs of the cell. These changes allow the amoeboid movement with which the cell can move.

In prokaryotic cells, most of the chemical reactions of metabolism take place in the cytosol, and others take place in the membranes. In eukaryotes, although many metabolic pathways occur in the cytosol, others occur in the organelles.

The cytosol is involved in the regulation of intracellular pH.

Cytosol proteins act as essential enzymes for cell life due to their involvement in metabolic processes:

• Glycogenogenesis, glycogen synthesis reactions.
• Glycogenolysis, glycogen degradation processes.
• Biosynthesis of amino acids and protein synthesis.
• Modifications applied to newly formed proteins.
• Biosynthesis of fatty acids.
• Many of the reactions involving ATP and tRNA.

All these processes require communication between the nucleoplasm and the cytosol, which takes place through the pores of the nuclear membrane.