Zytosol

Zytosol is the term used in German-language biology for what is known in English as the cytosol. It is the aqueous, gel-like component of the cytoplasm that fills the cell interior and surrounds organelles, serving as the medium in which many cellular processes occur. The Zytosol is distinct from the cytoplasm as a whole, which also includes organelles and other insoluble structures; the cytosol itself refers specifically to the fluid portion and its dissolved constituents.

Composition and physical properties

The Zytosol is primarily water, containing dissolved ions such as potassium, sodium, chloride, magnesium, and calcium, along with a wide array of small molecules, metabolites, nucleotides, and soluble enzymes. It also hosts a large number of cytosolic proteins, including enzymes that drive central metabolic pathways, and supports the polymeric networks of the cytoskeleton. Macromolecular crowding within the Zytosol influences reaction rates and diffusion. The exact composition and viscosity can vary among cell types and in response to physiological conditions.

Functions and significance

The Zytosol provides the milieu for many metabolic pathways, including glycolysis, nucleotide and amino acid synthesis, and other cytosolic reactions. It is the site of translation by free ribosomes and houses numerous signaling molecules and metabolic enzymes. The ionic composition and pH of the Zytosol help regulate enzyme activity, protein folding, and osmotic balance, while diffusion within the fluid supports rapid distribution of metabolites and cofactors.

Relationship to the cell

Cytoplasm comprises the Zytosol plus membrane-bound organelles. Thus, the Zytosol represents the soluble, non-membrane-bound portion of the cytoplasm where many essential, rapid-response processes take place. In German literature, Zytosol and cytosol are used interchangeably to denote this fluid component.