Which statement about peptide hormones is FALSE?
◦ Peptide hormones in the bloodstream are always bound to carrier proteins.
◦ Peptide hormones are first synthesized as prohormones.
◦ Peptide hormones remain in circulation for relatively short periods of time.
◦ Prohormones can be activated before their release by post-translational modification.
◦ Peptide hormones interact with receptors on the surface of their target cells.