PATHOLOGY

Detailed explanation-1: -G-protein-coupled receptors (GPCRs) are the largest and most diverse group of membrane receptors in eukaryotes. These cell surface receptors act like an inbox for messages in the form of light energy, peptides, lipids, sugars, and proteins.

Detailed explanation-2: -G protein-coupled receptor (GPCR), also called seven-transmembrane receptor or heptahelical receptor, protein located in the cell membrane that binds extracellular substances and transmits signals from these substances to an intracellular molecule called a G protein (guanine nucleotide-binding protein).

Detailed explanation-3: -G-protein interactions and inhibition of cellular reactions. GH-releasing hormone binds to its receptor (R1) and activates the Gs-protein that turns on adenylyl cyclase (AC) to synthesize cyclic adenosine monophosphate (cAMP) from ATP. cAMP acts as a second messenger to mediate release of GH.

Detailed explanation-4: -The G protein activates an enzyme called adenylyl cyclase. When activated, adenylyl cyclase converts a large number of ATP molecules into signaling molecules, called cyclic AMP (cAMP). Because cAMP carries the message of the first messenger (epinephrine) into the cell, cAMP is referred to as a second messenger.