How would signaling be affected if a mutation caused a g protein to replace gdp with gtp on its own without needing to be activated by the g protein-coupled receptor? the signal would not be affected and signaling would only occur when a ligand bound to the receptor. the signaling would be blocked because g protein would be active but unable to signal due to the lack of a bound ligand. the signaling pathway would be activated even when no ligand was present. the signaling would be blocked because replacement of gdp with gtp would deactivate the g protein.