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Progression of received information from one form into another.
Such signal transduction is usually employed for the sake of movement of signal over distances, modification of what is capable of being aware of the signal, and/or as a means of signal amplification so as to increase the potential for further information reception.
Movement can be simply from one side of a lipid bilayer to the other, which is typically the case for receptor proteins that also are membrane proteins, i.e., as embedded in a cell's plasma membrane. As is the case with excitable membranes as seen particularly in neurons, movement from one side of the membrane to the other can be linked with signal progression in the plane of the membrane, i.e., outward and so consequently across the surface of a cell.
Most signal transduction pathways penetrate into the cell, with transduction involving conversion of signal from one type of molecule, or ion, to another. Thus, proteins may be phosphorylated or what are known as second messengers may be produced, with specifics differing from system to system.
These processes have the effect of increasing the number of signal molecules, thereby literally increasing the signal, though not in the same form as when the signal originated. The result is an enhancement of the on-off nature of signals, where when the signal is present there is a substantial change in the internal chemistry of cell whereas when signal is absent the cell quickly returns to normal, non-transducing state.
The formation of the signal progressions also has the effect of converting the signal into a type that can be received by the end point of the signal transduction pathway, that is, resulting in a response. Signals thus are received by receptor proteins, are converted into new forms and then amplified in terms of the number of signalling molecules, and often amplified rather substantially. Finally, these conversions result in the creation of a specific signal forms that serve to directly stimulate the cell's response.
A signal transduction pathway can start with as few as one signal molecule binding to a receptor protein, move that signal into the cell, create a substantial change inside of the cell, and then reach the actual targets of the signal transduction pathway, resulting in a response. All of the steps between binding and response represent various aspects of signal transduction.
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