Question

Describe how the signal transduction pathway that involves G proteins is similar to the signal transduction pathway involving inositol triphosphate. In a second paragraph describe how these 2 signal transduction pathways differ from one another. In a third paragraph describe how these 2 pathways are turned off.

Answer 1

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. Both involves in the second messanger. G protein–coupled receptors (GPCRs) are a family of integral transmembrane proteins that possess seven transmembrane domains and are linked to a heterotrimeric G protein. Signal transduction by a GPCR begins with an inactive G protein coupled to the receptor; the G protein exists as a heterotrimer consisting of Gα, Gβ, and Gγ subunits.Inositol trisphosphate or inositol 1,4,5-trisphosphate abbreviated InsP3 or Ins3P or IP3 is an inositol phosphate signaling molecule. It is made by hydrolysis of phosphatidylinositol 4,5-bisphosphate (PIP2), a phospholipid that is located in the plasma membrane, by phospholipase C (PLC). Increases in the intracellular Ca2+ concentrations are often a result of IP3 activation. When a ligand binds to a G protein-coupled receptor (GPCR) that is coupled to a Gq heterotrimeric G protein, the α-subunit of Gq can bind to and induce activity in the PLC isozyme PLC-β, which results in the cleavage of PIP2 into IP3 and DAG. G protein-coupled receptors (GPCRs) represent a major class of drug targets. Finally, GPCR signaling is the subject of regulation by RTKs and other tyrosine kinases, including tyrosine phosphorylation of GPCRs itself, of G proteins, and of downstream molecules such as members of the protein kinase C family.Together with diacylglycerol (DAG), IP3 is a second messenger molecule used in signal transduction in biological cells. While DAG stays inside the membrane, IP3 is soluble and diffuses through the cell, where it binds to its receptor, which is a calcium channel located in the endoplasmic reticulum. It is the result of decrease in the cellular response to a second messenger. The most obvious method for turning off a signal is the dissociation of the ligand from the receptor. Ligand dissociation can be induced (a cellular process),or can occur due to a decrease in the circulating ligand concentration.