Hormone molecule Hormone-receptor combination Receptor cell Receptor membrane Membrane molecule enzyme (b) c ATP AMP d ctve一 Active er Cellular changes Nucleus cytopasm Figure 10.3 Mechanism of nonsteroid hormone action. (a) a nonsteroid hormone approaches a cell and (b)combines with a receptor in the cell membrane. (c) This activates a membrane enzyme that (d) converts ATP into cyclic AMP, which, in turn, (e) activates additional enzymes that produce changes in cellular function