BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 15. INTEGRATION OF METABOLIC PATHWAYS. HORMONES

15.4. Mechanisms of Hormone Action

The initial step in the Action of Hormones on a target Cell is the interaction of the hormone with cellular receptors. Chemically, Hormone Receptors are Proteins located either within The Plasma Membrane or inside The Cell. The interaction between hormones and their receptors is highly specific. Upon hormone binding, the metabolic rate in target Cells changes As a result of an alteration in either enzyme activity or enzyme synthesis (Fig. 15.5).

Class="center">

Fig. 15.5. MAIN STAGES OF hormonal signal Transduction

Receptors located on the cell surface bind Peptide Hormones and catecholamines. Such receptors comprise three functional domains. Located on the outer surface of the membrane is the

N-terminal glycosylated region of the polypeptide chain, which forms the recognition domain. The second domain is transmembrane, and the third is cytoplasmic. Receptors for steroid and THYROID HORMONES are located inside the cell. Intracellular receptors may be localized either in the Cytosol (for glucocorticoids) or in The Nucleus (for androgens, estrogens, and thyroid hormones).