Each receptor has the ability to recognise one type of growth factor and only that growth factor. When a receptor molecule recognises the correct type of growth factor on the outside of the cell, it activates its 'tail' which sends a signal inside the cell. Although we know what most of these internal signals consist of, our research has revealed a highly complex picture of one signal causing another signal, with different signalling pathways, from different growth factors, affecting each other. Whilst we do not yet fully understand how this signalling network works, we do understand what it ultimately does. The purpose of the signals is to turn on and off the set of genes that control cell growth and division.
Genes are the coded instructions for all the functions of cells.
They work by storing the information necessary to make the protein molecules needed for a particular function. Thus, all the complex processes involved in cell division are ultimately the work of a special set of proteins probably over a hundred of them. Normally, these proteins are not found inside a cell, so it does not divide. However, when the right growth factor binds to the right receptor and sends a signal into the cell, the genes coding for these proteins are activated and they make the proteins. Once the cell division proteins are present, they start to work and the cell begins to divide.