AP BIOLOGY

Detailed explanation-1: -So called because they bind guanine nucleotides, G proteins are also capable of hydrolyzing guanosine triphosphate (GTP) to guanosine diphosphate (GDP). This enzymatic activity is used as a regulatory switch to convert the G protein from a GTP-bound, functionally active state to a GDP-bound inactive state.

Detailed explanation-2: -Regulation of G-proteins by RGS proteins. A large family of RGS (regulators of G-protein signaling) proteins has been identified. After the active GTP-bound G exerts its effect on downstream effectors, this activation must be highly regulated to maintain the appropriate signal strength and duration.

Detailed explanation-3: -G proteins are molecular switches that are activated by receptor-catalyzed GTP for GDP exchange on the G protein alpha subunit, which is the rate-limiting step in the activation of all downstream signaling.

Detailed explanation-4: -They are small (20-kDa to 25-kDa) proteins that bind to guanosine triphosphate (GTP). This family of proteins is homologous to the Ras GTPases and is also called the Ras superfamily GTPases.

Detailed explanation-5: -Mechanism. GAP are heavily linked to the G-protein linked receptor family. The activity of G proteins comes from their ability to bind guanosine triphosphate (GTP). Binding of GTP inherently changes the activity of the G proteins and increases their activity, through the loss of inhibitory subunits.