Cell division is the creation of new ‘daughter’ cells from a single ‘parent’ cell. At some point in their life cycle, all cells will divide and the new cells could be exactly the same as the original cell or share half of the same material. Some cells will only ever divide once in their life cycle while others will continuously divide. There are several reasons that the cells in the body divide or copy themselves: cells don’t last and wear out eventually, repairing damaged tissue, and because the body requires new cells as it grows. While this explains the reason why cell division is needed, how exactly is the division initiated or by what?
Cell division does not just occur randomly. The cell will divide based upon the conditions in its environment and as a result of its genetic code. Cells receive extracellular chemical signals either from the body or from other cells that will cause them to start dividing, almost like a chain reaction. Before they receive these signals, the stage of the cell cycle where division occurs is blocked. These chemical signals are referred to as mitogens and there are more than one type.
Cells are primarily induced into dividing because of presence of growth factors. The surface of the cell membrane has different receptor areas for these specific regulatory proteins. Once the receptor area is filled with the protein (growth factors), it triggers a signal that activates proteins within the cell and begins the cell division process. There are about fifty different proteins of this type that will stimulate many different types of cells to divide in the body.
Other cells can also release chemical compounds that will cause the nearby cells to start dividing. An example of these are cytokines, which are molecules that can be produced in certain cells of the nervous and immune system. They are but one example in a category of signaling molecules which are used by cells for intercellular communication.
In studies performed on chicken cells, the substance thrombine has been shown to induce cell division. This chemical is present in a variety of processes in the body and could initiate cell division when placed in contact with a cell membrane, similar to the two mitogens mentioned above.
Cells divide as a result of different reasons but the exact cause of the division is a result of the presence of chemical compounds — proteins and molecules in the extracellular fluid. These substances come into contact with the cell membrane and trigger the cell to initiate division. They are either produced by another part of the body or the surrounding cells. The end result is that the exposed cells will initiate the part of the cell cycle which allows them to divide and create ‘daughter’ cells.