Figure 6.

An overview of major signal transduction pathways. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone and neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation and cell proliferation. Many tumor suppressor genes effect signal transduction pathways which regulate apoptosis, also known as “programmed cell death” (courtesy: http://en.wikipedia.org/wiki/File:Signal_transduction_v1.png)