Answer:
The hormones that are
derivatives of amino acids, polypeptides or proteins are called peptide
hormones. These being insoluble in lipids cannot enter the target cell.
These act at the
surface of target cell as primary messengers and bind to the cell-surface receptor
forming the hormone-receptor complex.
It involves
following steps
(i) Hormone
called first messenger attaches to the cell surface receptor protein on the outer
surface of plasma membrane of the target cell, forming a hormone-receptor complex.
(ii) This
complex activates the enzyme adenyl cyclase.
(iii) Adenyl
cyclase catalyses the conversion of ATP to cyclic AMP on the inner surface of plasma
membrane.
(iv) cAMP
serves as the second messenger or intracelluar hormonal mediator delivering
information inside the target cells. This activates appropriate cellular enzyme
system by cascade effect. Which induces the cell machinery to perform its
specialised function.
(v) cAMP has
a very short existence. It is rapidly degraded by the cAMP phosphodiesterase.
Water soluble
hormones, such as amines, peptides, proteins and glycoproteins exert their
control through the cyclic AMP These are quick acting hormones and produce
immediate effect.
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