What property prevents the ligands of cell-surface receptors from entering the cell?

Cyclic AMP functions as a second messenger to:

(a) Build proteins and catalyze specific reactions

(b) Activate adenylate cyclase

(c) Open ion channels and activate key enzymes in the cytoplasm

(d) Bind the hormone–receptor complex to DNA segments

How would blocking the activity of phosphodiesterase (PDE) affect a cell that responds to hormonal stimulation by the cAMP second messenger system?

A researcher observes that stimulation by a particular hormone induces a marked increase in the activity of G proteins in the target plasma membrane. The hormone being studied is probably:

(a) A steroid

(b) A peptide

(c) Testosterone

(d) Estrogen

(e) Aldosterone