A single hormone molecule touching the membrane can end in thousands of response molecules inside, because every tier of the kinase cascade multiplies the count again. The higher the ligand concentration outside, the more plainly the amplification shows: a tiny input still produces an enormous output. Two routes differ completely: a GPCR sits in the membrane and relays its message indirectly through the second messenger cAMP, while a lipid-soluble steroid passes straight through the membrane into the nucleus. In cancer a receptor jams in the on position, so the whole cascade keeps running.
A single hormone molecule touching the membrane can end in thousands of response molecules inside, because every tier of the kinase cascade multiplies the count again. The higher the ligand concentration outside, the more plainly the amplification shows: a tiny input still produces an enormous output. Two routes differ completely: a GPCR sits in the membrane and relays its message indirectly through the second messenger cAMP, while a lipid-soluble steroid passes straight through the membrane into the nucleus. In cancer a receptor jams in the on position, so the whole cascade keeps running.
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