Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellular response. There are three stages in the process of cell signaling or communication:Reception-a protein at the cell surface detects chemical signals.Transduction-a change in protein stimulates other changes including signal-transduction pathways.Response-almost any cellular activity. There are four basic categories of chemical signaling found in multicellular organisms: paracrine signaling, autocrine signaling, endocrine signaling, and signaling by direct contact.Cells have proteins called receptors that bind to signaling molecules and initiate a physiological response. Two major signal transduction pathways, cAMP-dependent pathway and mitogen-activated protein kinase (MAPK) pathway, will be discussed. Both pathways are highly relevant to modulation of differentiation and proliferation in T. cruzi by phosphorylating a set of specific substrate proteins.First, reception, whereby the signal molecule binds the receptor. Then, signal transduction, which is where the chemical signal results in a series of enzyme activations. Finally, the response, which is the resulting cellular responses. Signal transduction is a cascade of biochemical reactions that take place in a cell when a signal molecule such as hormone or biomolecule binds to a receptor