Signal Transduction

To survive, an organism must constantly adjust its internal state to changes in the environment. To track environmental changes, the organism must receive signals. These may be in the form of chemicals, such as hormones or nutrients, or may take another form, such as light, heat, or sound. A signal itself rarely causes a simple, direct chemical change inside the cell. Instead, the signal sets off a chain of events that may involve several or even dozens of steps. The signal is thereby transduced, or changed in form. Signal transduction refers to the entire set of pathways and interactions by which environmental signals are received and responded to by single cells.

Signal transduction systems are especially important in multicellular organisms, because of the need to coordinate the activities of hundreds to trillions of cells. Multicellular organisms have developed a variety of mechanisms allowing very efficient and controlled cell-to-cell communication. Though we take it for granted, it is actually astonishing that our skin, for example, continues to grow at the right rate to replace the continuous loss of its surface every day of our lives. This tight regulation is found in every tissue of our body all of the time, and when this fine control breaks down, cancer may be the result. Clearly the molecular mechanisms behind this astounding level of control must be powerful, versatile, and sophisticated.