which choice describes the activation steps of a g protein-coupled receptor properly (and in correct order)?
A. Ligand binds to receptor, G protein activated, effector protein activated, second messenger made available
B. Ligand binds to receptor, second messenger activated, G protein turned on, protein kinase activated
C. Protein kinase activated, ion channel opened, ions enter and activate second messenger, G protein turned on
D. Ion channel opened, G protein activated, second messenger synthesized, phosphatase ends signal