tsütosool

Tsütosool, known in English as the cytosol, is the aqueous component of the cytoplasm that surrounds organelles and is enclosed by the cell membrane. In Estonian terminology, tsütosool denotes this fluid phase inside the cell. It is a viscous, water-rich matrix in which many cellular processes occur.

The cytosol is predominantly water but contains dissolved ions, small molecules, and a soluble protein fraction. It hosts enzymes that drive core metabolic pathways such as glycolysis and parts of the pentose phosphate pathway, as well as various other anabolic and catabolic reactions. The cytosol also contains the cytoskeleton, ribosomes, and a variety of soluble signaling molecules, cofactors, and metabolites. While some ribosomes are attached to the endoplasmic reticulum, many are freely suspended in the cytosol.

Functions of the tsütosool include serving as the medium for diffusion and transport of nutrients, metabolites, and signaling molecules; providing the environment for many metabolic reactions; and supporting protein synthesis by ribosomes that operate within this fluid phase. It also acts as a structural and organizational space, interacting with organelles through cytoskeletal networks and signaling pathways.

Distinction from cytoplasm: the cytoplasm comprises the entire content inside the cell membrane, including the cytosol plus all organelles, whereas the tsütosool specifically refers to the fluid component. In cell biology, the cytosolic (free) fraction is often isolated experimentally to study soluble enzymes and cytosolic signaling processes.