ABSTRACT

Binding of the ligand to the receptor causes a conformational change in the receptor that initiates a sequence of reactions in the target cell leading to a change in cellular function. The signaling molecules or hormones can be classified based on their solubility and the location of their receptor. Cell signaling can be classified into three distinct types based on the distance over which the signaling molecule acts. In endocrine signaling, the signaling molecule acts on target cells distant from its site of synthesis in cells of an endocrine organ. In paracrine signaling, the signaling molecule affects only target cells close to the cell from which it was secreted. The third type of cell signaling is autocrine signaling, where a cell responds to a molecule that it has produced itself. The principal lipophilic hormones that bind to receptors located in the plasma membrane are the prostaglandins, a family of structurally similar compounds that are found in both vertebrates and invertebrates.