Which statement regarding Gprotein activation is TRUE Multip

Which statement regarding G-protein activation is TRUE? Multiple Choice G-proteins are activated when they are bound by an extracellular signaling molecule. G-proteins are activated by the alpha subunit separating from the beta/gamma subunit. G-proteins are activated by active G-protein-linked receptors. G-proteins are activated by Ca^2+. Only the alpha subunit of the G-protein is active.

Solution

All are true.

Mechanism:

When a hormone, Ca++ or extracellular signaling molucule bind to GPCR (note: G protein is in inactive state and G aplha has GDP on its binding site), causes activation and a allosteric change takes place which triggers G alpha and GDP replaced by GTP. GTP activates G alpha to dissociate from G beta gamma.