Chemotaxis

Chemotaxis is a basic guidance mechanism employed by cells and organisms to move toward beneficial targets or environments and to avoid undesired ones. This mechanism, which is prevalent from bacteria to human beings, consists of two basic processes. One is the formation by diffusion of a concentration gradient of a specific chemical. The other is the sensation of this gradient by a cell/organism and the modification of its direction of movement up or down the chemical gradient (the chemical being defined as chemoattractant or chemorepellent, respectively). Although chemotaxis is a universal mechanism and so are the steps that constitute it (gradient sensing by receptors, signal transduction and amplification, and movement response), the processes that underlie this mechanism are diverse.