AP BIOLOGY

Detailed explanation-1: -Upon activation by a ligand, the GPCR undergoes a conformational change and then activate the G proteins by promoting the exchange of GDP/GTP associated with the G subunit.

Detailed explanation-2: -Binding of GDP allows the subunit to bind to the and subunits to form an inactive trimer. Binding of an extracellular signal to a G-protein-coupled receptor allows the G-protein to bind to the receptor and causes GDP to be replaced with GTP (Figure 8.5A).

Detailed explanation-3: -They are activated in response to a conformational change in the GPCR, exchanging GDP for GTP, and dissociating in order to activate other proteins in a particular signal transduction pathway. The specific mechanisms, however, differ between protein types.

Detailed explanation-4: -Activation of the receptor by the neurotransmitter dopamine causes the alpha subunit to exchange its GDP for a GTP.

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.