Mechanisms
of Hormone Action
Hormones trigger
actions in specific target cells,
after binding to an appropriate receptor. Receptors
are membrane proteins that bind to hormones. A certain hormone receptor located
on a specific target cell can only bind to one type of hormone. More than fifty
human hormones have been identified; all act by binding to receptor molecules.
The binding hormone causes a change in the shape of the receptor. This
alteration of the receptor’s molecule causes the cell to respond to the
hormone.
here are two different
mechanisms of hormone action on all target cells:
Steroid and non – steroid hormones
§ Nonsteroid
Hormones
Nonsteroid hormones
(water soluble) do not enter the cell but bind to plasma membrane receptors,
generating a chemical signal (second
messenger) inside the target cell. Five different second messenger
chemicals, including cyclic AMP have been identified. Second messengers
activate other intracellular chemicals to produce the target cell response.
§ Steroid
Hormones
The second mechanism
involves steroid hormones, which pass through the plasma membrane and act in a
two step process. Steroid hormones bind, once inside the cell, to the nuclear
membrane receptors, producing an activated hormone-receptor complex. The
activated hormone-receptor complex binds to DNA and activates specific genes,
increasing production of proteins.
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