Hydrophilic and some lipophilic hormones bind to cell surface receptors. These are necessary  membrane  proteins  located  in the plasma  membrane  which  bind  the  signaling  molecule  (ligand)  with  high  affinity.  Ligand binds to a particular site on the receptor in much the same way as a substrate binds to an enzyme. The Binding of the ligand to the receptor should cause a conformational modification in the receptor or endorse dimerization of two receptors which initiates a series of reactions in the goal cell (often referred to as signal transduction) leading to a modification in cellular function. The sharing of receptors varies on variety cells and there is frequently more than one kind of receptor for a specific ligand permitting variety goal cells to respond differently to the same signaling molecule. The Cell surface receptors can be classified into three  major  classes  depending  on how they transmitted  the information  from  the ligand  to the  interior  of the  cell:  ion  channel-linked receptors, enzyme-linked  receptors and receptors of G protein-coupled .