|MoBio||Overview of Cell Signaling||Chapter 6|
A cell needs to communicate with its environment so that it can make appropriate responses. The external signal may enter a cell via four major pathways:
They are discussed in Sections B, C, D and E.
In many cases, the signal continues to propagate within the cell and often reaches nuclear DNA to express proteins. The intracellular signaling is discussed in Section F. Section G deals with the mechanism and signaling in apoptosis (programmed cell death).