Chapter 12 BIOCHEMICAL SIGNALING

An illustration depicts the chapter opener

The ability of cells to receive and act on signals from outside the plasma membrane is fundamental to life. Cells and organisms constantly sample the surrounding medium for nutrients, oxygen, light, and sexual partners, and for the presence of noxious chemicals, predators, or competitors for food. These signals elicit appropriate responses, such as motion toward food or away from toxic substances. In multicellular organisms, cells exchange hundreds of signals — neurotransmitters, hormones, key metabolites — which trigger appropriate responses in such cellular activities as metabolism, cell division, embryonic growth and development, movement, and defense. In all these cases, the signal represents information that is detected by specific receptors and converted to a cellular response, which always involves a chemical process. This conversion of information into a chemical change, signal transduction, is a universal property of living cells.

In this chapter, we present examples of specific biological signaling systems from which we have acquired our current understanding of the biochemistry of signal transduction in animals. We emphasize the following principles: