BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 15. INTEGRATION OF METABOLIC PATHWAYS. HORMONES

15.4. Mechanisms of hormone action

15.4.2. Mechanism of action of steroid and thyroid hormones

Intracellular receptors bind to steroid and THYROID Hormones, as well as to active forms of Vitamins A and D (Fig. 15.7). This means that signal Transduction is only possible if these hormones cross Cell/30.html">The Plasma Membrane of the target cell. Receptors can be located in the Cytoplasm or in The Nucleus. Cytosolic receptors are associated with chaperone Proteins. The interaction of the hormone with the receptor induces a conformational change in the receptor and decreases its affinity for chaperone proteins. The hormone-receptor complex enters the nucleus, where it interacts with a regulatory nucleotide sequence in the DNA—an enhancer or a silencer. This, respectively, increases or decreases the accessibility of the promoter to RNA polymerase, thereby regulating The rate of METABOLISM/31.html">Transcription. Consequently, the rate of Translation is regulated, and the levels of specific proteins, including Enzymes, are altered.

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Fig. 15.7. Hormonal signal transduction via intracellular receptors