Anger And It Control

Anger And It Control

Cell Communication
PRELIMINARY VERSION © 2003 Garland Science
General Principles of Cell Signaling
Signals Can Act over Long or Short Range Each Cell Responds to a Limited Set of Signals Receptors Relay Signals via Intracellular Signaling Pathways Nitric Oxide Crosses the Plasma Membrane and Activates Intracellular Enzymes Directly Some Hormones Cross the Plasma Membrane and Bind to Intracellular Receptors Cell-Surface Receptors Fall into Three Main Classes Ion-channel–linked Receptors Convert Chemical Signals into Electrical Ones Many Intracellular Signaling Proteins Act as Molecular Switches

Individual cells, like multicellular organisms, need to sense and respond to their environment. A typical free-living cell—even a primitive bacterium—must be able to track down nutrients, tell the difference between light and dark, and avoid poisons and predators. And if such a cell is to have any kind of “social life,” it must be able to communicate with other cells. When a yeast cell is ready to mate, for example, it secretes a small protein called a mating factor. Yeast cells of the opposite “sex” detect this chemical mating call and respond by halting their progress through the cell cycle and reaching out toward the cell that emitted the signal (Figure 16–1). In a multicellular organism, things are much more complicated. Cells must interpret the multitude of signals they receive from other cells to help coordinate their behaviors. During animal development, for example, cells in the embryo exchange signals to determine which specialized role each cell will adopt, what position it will occupy in the animal, and whether it will survive, divide, or die; later, a large variety of signals coordinate the animal’s growth and its day-to-day physiology and behavior. In plants, too, cells are in constant communication with one another. Their interactions allow the plant to respond to the conditions of light, dark, and temperature that guide the cycle of its growth, flowering,...