The cytoplasm (in eukaryotes) is the fluid content inside the plasma membrane excluding the nucleus and its contents. It means, all the organelles plus their contents, cytoplasmic matrix / fluid, macromolecules and ions put together constitutes “cytoplasm”. Sometimes it is important to differentiate between the cytosol and the cytoplasm. The cytosol is defined as all the contents in the cytoplasm barring cell organelles and materials enclosed in them. So cytosol is the fluid component of cytoplasm – made up of water, dissolved ions, small and macromolecules required for proper functioning of cell.
Functions of Cytoplasm:
Cytoplasm is crucial for existence of cell and eventually life. It performs the following functions:
- Cytoplasm provide a medium for the organelles to float and organic molecules to dissolve for their normal function.
- Many important cellular functions such as protein synthesis, cell division ( mitosis and meiosis) and glycolysis (first stage of cellular respiration) occurs in cytoplasm.
- Cytoplasm provides a medium for hormones to move in the cell.
- Many signal transduction pathways occur in the cytoplasmic matrix. This allows signals to be passed between cell membrane, nucleus and organelles.
- Helps in transport of molecules from its site of synthesis to their destination.
Composition of cytosol:
Cytosol is majorly composed of water (70%), but it’s jelly like consistency comes from many dissolved proteins (which are not bound to cell membranes or cytoskeleton). Apart from proteins, cytosol also has other organic molecules such as glucose and other simple sugars, fatty acids, nucleic acids, amino acids. It also consists of Ions of sodium, potassium, calcium, and many other elements in dissolved state. There is a major difference in concentration of Potassium and sodium ions between cytosol and extra cellular fluid which is important for osmoregulation and hence for transport of molecules. The low concentration of calcium ion in cytosol is responsible for it acting as secondary messenger in calcium signaling. This difference in concentration of substances in the cytosol is affected by channels in the cell membrane.