Transduction of Signals

Abstract

Communication between the cells of a multicellular organism is a necessity for its life. Signaling chains are needed for the coordination of the processes inside each cell as well. The majority of the signals are transmitted by diffusion of small molecules which are secreted by other cells. The signal molecules cannot, however, pass through the cell membrane. To overcome the barrier, they bind specific receptors on the cell surface. The receptors are transmembrane proteins, and the binding of a signal molecule at the external end of the protein causes a conformational change at its internal end. This change allows the binding of another signaling molecule with the internal end of the receptor. The intracellular parts of signaling chains can include a few more signaling molecules and receptors. Special attention is paid to one very important class of signaling chains based on G-proteins. We also consider signal transduction in the nerve cells. In this case, the signal has to be transmitted very fast, usually in milliseconds, from one end of a body to another. Therefore, the signal cannot be transmitted by diffusion. Instead, it is transmitted along very long bodies of nerve cells as a fast-spreading electric potential.