Overview of Cell Signaling

Figure 6-A-1.  Major pathways for signals to enter a cell.

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:

1. Hydrophobic molecules.
2. Ion channels.
3. G-protein-coupled receptors.
4. Enzymes.

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).