Some G proteins produce a cellular response through

theinositol triphosphate IP3/Ca2+pathway. Explain how the binding of

a ligand to the receptor produces aresponse in this pathway. What

is the target enzyme and secondmessenger in this pathway? Name one

specific cell functionregulated by the IP3/Ca2+pathway.

The ligand binds with the receptor that causes change in the conformation and allows interaction of 5th and 6th helix of receptor with the G-protein. This allows a GDP exchange with GTP in alpha-subunit of G-protein. This subunit detached from the beta and gamma subunit and gets interact with the effector molecule.

The target enzyme, phospholipase converts the PIP2 into IP3 and DAG. The DAG (diacylglycerol) activates the protein kinase-C. The IP3 (inositol 1,4,5 triphosphate) travels to the cytosol and binds with the SER. This increases the cytosolic ca2 + concentration.

The Ip3 act as a second messenger in this pathway. This pathway specific function is to regulate the movement of calcium from the storage organelles, cellular reaction and cell proliferation.