The evolution of signaling molecules has made it possible for cells of multicellular organisms, such as humans, to communicate with one another in simple and complex ways. Signaling molecules may be used to transmit information between cells (extracellular or intercellular signaling), or they may be involved in signaling cascades inside cells (cytoplasmic or intracellular signaling). Test your basic knowledge of signaling molecules by taking this simple quiz.
(1) Classical and peptide neurotransmitters are released from neurons via the __________ secretory pathway.
(2) Steroid and thyroid hormones are released from endocrine cells via the __________ secretory pathway.
(3) In general, peptide hormones have shorter half-lives than steroid and thyroid hormones.
(4) In the biosynthetic pathway of catecholamines, the enzyme phenylalanine hydroxylase catalyzes the following reaction:
(5) In the biosynthetic pathway of catecholamines, the enzyme tyrosine hydroxylase catalyzes the following reaction: