Reception, transduction and cellular response are the stages of cell signaling. Cell signaling is part of a complex communication system that governs basic cellular activities and coordinates the cell activities. Cell–signaling/ cellular conversation can be briefly explained in three stages.
Reception: In this stage the signal molecule is detected by the receptor protein of target cell. The signal molecule generally comes from outside and is new to the target cell, where as the receptor molecules/proteins are located outside/ inside to the target cell. In other terms reception can be defined as the target cell detection of signal molecule that is coming from outside of the cell.
Transduction: This is second stage of cell signaling where the binding of signal molecule triggers the receptor protein of the target cell initiating the process of transduction.
Response: It is the third stage of cell signaling where the transduced signal finally triggers a specific cellular response. This response may be in the form of cellular activity–such as catalysis by an enzyme (Eg: Glycogen phosphorylase), rearrangement of the cytoskeleton, or activation of specific genes in the nucleus.
Signaling molecule binds to a receptor protein that is complementary in shape to a specific site of receptor, causing it to change shape and attaches there, like a key in a lock or a substrate in the catalytic site of an enzyme. Here the signaling molecule behaves as a ligand that generally causes a receptor protein to undergo a change in shape and causes the aggregation of two or more receptor molecules, which leads to further molecular events inside the cell.