AP BIOLOGY

Detailed explanation-1: -Heterotrimeric G proteins consist of three distinct subunits, , and . These proteins couple the activation of diverse types of plasma membrane receptor to a variety of intracellular processes.

Detailed explanation-2: -A G protein-coupled receptor (GPCR) functions not only as a monomer or homodimer but also as a heterodimer with another GPCR. GPCR heterodimerization results in the modulation of the molecular functions of the GPCR protomer, including ligand binding affinity, signal transduction, and internalization.

Detailed explanation-3: -The heterotrimeric guanine nucleotide-binding proteins (G-proteins) function to transduce signals from this vast panoply of receptors to effector systems including ion channels and enzymes that alter the rate of production, release or degradation of intracellular second messengers.

Detailed explanation-4: -G proteins are classified into four families according to their subunit: Gi, Gs, G12/13, and Gq (Figure 1). The Gs and Gi families regulate adenylyl cyclase activity, while Gq activates phospholipase C and G12/13 can activate small GTPase families (10).

Detailed explanation-5: -Heterotrimeric G proteins have a crucial role as molecular switches in signal transduction pathways mediated by G-protein-coupled receptors. Extracellular stimuli activate these receptors, which then catalyse GTP-GDP exchange on the G protein alpha-subunit.