What is the significance of non-steroid hormones?

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Non-steroid hormones are water-soluble and cannot cross the cell membrane, so they exert their effects by binding to receptors on the cell surface. This binding activates enzymes such as adenylate cyclase, which raises the level of cyclic AMP inside the cell. That second messenger then triggers a cascade of phosphorylation events, amplifying the signal and producing a rapid cellular response. This surface-receptor, cAMP-driven pathway is the hallmark of non-steroid hormone action. The other ideas describe diffusion through the membrane or needing transport proteins, which don’t fit how non-steroid hormones typically work.