Cytosol is the fluid that’s found inside living cells. More specifically, it’s the water-based fluid in which organelles, proteins and other structures of the cell live. Also known as the cytoplasmic matrix, it constitutes most of the intracellular fluid (ICF). Cytosol is often confused with cytoplasm, however, which is an entirely different entity within a cell.
While cytosol refers to the water and anything soluble that is dissolved in it, such as soluble proteins and ions, the cytoplasm consists of cytosol and certain insoluble suspended particles (e.g., ribosomes).
As you may already know, the cell is the basic unit of life. Every living being in the world is made of billions upon billions of cells, which are responsible for a number of essential life processes. The function of these cells is determined by tiny organs (or organelles) that are present inside the cell.
Cytosol is a crucial cellular component that provides structural support for these organelles.
You see, a cell is like a plastic bag filled with fluid. The fluid it contains is the cytosol, while the bag itself is the cell membrane.
The majority of cytosol is water, which makes up nearly 70% of the total volume of a cell. While the pH of the intracellular fluid is 7.4, human cytosolic pH lies between 7.0-7.4, and is typically higher when the cell is growing. In addition to water, cytosol also consists of small molecules, dissolved ions and large water-soluble water molecules (e.g., proteins).
Note that the concentrations of the other ions present in the cytosol are different from those ions present in the extracellular fluid. In addition to that, higher amounts of charged macromolecules (e.g., proteins) and nucleic acids are present inside the cytosol than outside of the cell structure.
Interestingly, cytosol does not have a single, well-defined function; rather, it serves as a site for a number of intracellular processes (e.g., signal transduction – a cellular mechanism that converts a stimulus into a response within the cell, from the cell membrane to sites present within the cell).
A number of enzymatic activities require cytosol, as enzymes often require certain pH levels, salt concentrations and other environmental conditions that are appropriately fulfilled by cytosol. In addition to that, cytosol provides structural support to organelles. In fact, most cells depend on the volume of cytosol to make space for chemicals to move within the cell.
Cytosol vs Cytoplasm
Cytosol is often confused with cytoplasm, but these two are entirely different entities related to a living cell. While cytoplasm consists of all the contents found inside a cell (excluding the nucleus), cytosol is just the liquid or aqueous part of the cytoplasm. In other words, cytoplasm is the area of space outside the nucleus and consists of cytosol and other organelles.
It is important to note that cytosol is a critical element of the cytoplasm. In a prokaryotic cell, cytosol is the host of almost all chemical reactions and metabolic processes that take place within the cell. Also, cytosol is the site for cell communication, while cytoplasm plays host to certain large-scale processes, such as cell division and glycolysis.
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