Cytosol

The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (<a href="/facts/Fluid_compartments/CYV4l60r">intracellular fluid</a> (ICF)). It is separated into compartments by membranes. For example, the <a href="/facts/Mitochondrial_matrix/tgC0ENLv">mitochondrial matrix</a> separates the mitochondrion into many compartments.
In the <a href="/facts/Eukaryotic_cell/SkwyPLMA">eukaryotic cell</a>, the cytosol is surrounded by the <a href="/facts/Cell_membrane/vAXSD0DT">cell membrane</a> and is part of the <a href="/facts/Cytoplasm/Wa0sE6xf">cytoplasm</a>, which also comprises the mitochondria, <a href="/facts/Plastid/INesmXK7">plastids</a>, and other <a href="/facts/Organelle/vhDFnGbs">organelles</a> (but not their internal fluids and structures); the <a href="/facts/Cell_nucleus/D7sFRa3c">cell nucleus</a> is separate. The cytosol is thus a liquid matrix around the organelles. In <a href="/facts/Prokaryotes/oYyvaDDH">prokaryotes</a>, most of the chemical reactions of <a href="/facts/Metabolism/WxDrm8k5">metabolism</a> take place in the cytosol, while a few take place in membranes or in the <a href="/facts/Periplasmic_space/eGSSXT3C">periplasmic space</a>. In eukaryotes, while many <a href="/facts/Metabolic_pathway/8Py8HKJd">metabolic pathways</a> still occur in the cytosol, others take place within organelles.
The cytosol is a complex mixture of substances dissolved in water. Although water forms the large majority of the cytosol, its structure and properties within cells is not well understood. The concentrations of <a href="/facts/Ion/3bePpDna">ions</a> such as <a href="/facts/Sodium/eYuSPu2V">sodium</a> and <a href="/facts/Potassium/FWPwS7Rj">potassium</a> in the cytosol are different to those in the <a href="/facts/Extracellular_fluid/hzm4qatP">extracellular fluid</a>; these differences in ion levels are important in processes such as <a href="/facts/Osmoregulation/zXEhVwD4">osmoregulation</a>, <a href="/facts/Cell_signaling/6oYAVP9I">cell signaling</a>, and the generation of <a href="/facts/Action_potentials/Sz8yCRqx">action potentials</a> in excitable cells such as endocrine, nerve and muscle cells. The cytosol also contains large amounts of <a href="/facts/Macromolecule/039ULSLg">macromolecules</a>, which can alter how molecules behave, through <a href="/facts/Macromolecular_crowding/RaSyR2hC">macromolecular crowding</a>.
Although it was once thought to be a simple solution of molecules, the cytosol has multiple levels of organization. These include <a href="/facts/Diffusion/KbAxroBa">concentration gradients</a> of small molecules such as <a href="/facts/Calcium/hf252CC0">calcium</a>, large complexes of <a href="/facts/Enzyme/DSI1Fh7y">enzymes</a> that act together and take part in <a href="/facts/Metabolic_pathway/8Py8HKJd">metabolic pathways</a>, and <a href="/facts/Protein_complex/GW11Ee34">protein complexes</a> such as <a href="/facts/Proteasome/8vTtg2MI">proteasomes</a> and <a href="/facts/Carboxysome/NY8LTF2f">carboxysomes</a> that enclose and separate parts of the cytosol.

Cytosol open-in-new

Cytosol