Cell Cycle
Cells are born, they grow and at some point they divide in order to give rise to a daughter cell or they die. This life cycle is what in biology we call the “Cell Cycle”. This process must be very tightly regulated, as uncontrolled division can lead to a variety of problems. If a cell that is “too young” divides prematurely or in suboptimal conditions, the progeny are less likely to be healthy. Conversely, if cells that are “too old” continue to divide, they pass on any genomic errors they have accumulated to the daughter cells. Worst of all are cells that do not know when to stop dividing, as they deplete the resources needed by other cells and can invade and damage healthy tissues.
Cell Signaling
In order for cells to respond to changes in their external and internal environments, they need an accurate system of communication.
In order to properly react to changes in its environment, a cell needs to know both what has occurred and what the response should be. This information is delivered by means of signaling networks and cascades, which can transmit this information from the cell surface to the nucleus.
For example, a cell infected by a virus sends out certain molecules to signal “danger”, which are then recognised by specific molecules on the surface of healthy neighbouring cells. This recognition triggers what is known as a signaling cascade, transmitting the signal step by step through the healthy cell to the nucleus. Once in the nucleus, it initiates an appropriate defence programme, which decreases the chance of getting infected by the virus and helps the immune system to fight the infection.