Asignal transduction inbiology is acellular mechanism. It converts astimulus into a response in the cell.[1] There are two stages in this process:
So, signal transduction starts with a signal to acell receptor, and ends with a change in cell function. In either step, the signal can be amplified. Thus, one signalling molecule can cause many responses.[1]
Receptors are in thecell membrane, with part of the receptor outside and part inside the cell. The chemical signal binds to the outer portion of the receptor, changing its shape. This causes another signal inside the cell. Some chemical messengers, such astestosterone, can pass through the cell membrane, and bind directly to receptors in thecytoplasm ornucleus.
Sometimes there is acascade of signals within the cell. With each step of the cascade, the signal can beamplified, so a small signal can result in a large response.[1] Eventually, the signal creates a change in the cell, either in the expression of theDNA in the nucleus or in the activity ofenzymes in the cytoplasm.
Most often, ordered sequences ofbiochemicalreactions inside the cell are involved. These are carried out byenzymes and linked through second messengers. So a "second messenger pathway" is produced. These things usually happen quickly, sometimes very quickly. They may last from milliseconds (in the case ofionflux) to days forgene expression.
The number ofproteins and othermolecules that take part increases during the process. So a 'signal cascade' develops anda relatively small stimulus may cause a large response.
Inbacteria and other single-cellorganisms, the transduction processes a cell has limits the number of ways it can respond to its environment. Inmulticellular organisms, lots of different signal transduction processes are used to coordinate the behavior of individual cells. By this means the function of the organism as a whole is organized. The more complex the organism, the more complex the repertoire of signal transduction processes the organism must possess.
Thus,sensing of both the external and internal environment at the cellular level, relies on signal transduction. Manydisease processes such asdiabetes,heart disease,autoimmunity andcancer arise from defects in signal transduction pathways. This highlights the critical importance of signal transduction to biology and medicine.[2]
These systems of communication between cells are extremely ancient, and are found in allmetazoa.[3]
{{cite book}}: CS1 maint: multiple names: authors list (link){{cite journal}}: CS1 maint: multiple names: authors list (link)