Question

Explain the mechanism of action of steroid hormones

Answer 1

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Mode Of Steroid Harmone Action Through Intracellular Receptors.

Steroid harmones are lipid-soluble and easily pass through the cell membrane of a target cell into the cytoplasm. In the cytoplasm they bind to specific INTRACELLULAR RECEPTORS(proteins) to form a harmone receptor complex that enters the nucleus. In the nucleus, harmones which interact with intracellular receptors (e.g., steroid harmones, iodothyromines, etc.) Most ly regulate gene expression or chromosome function by interaction of harmone-receptor complex with the genome. Biochemical actions result in physiological and developmental effects (tissue growth and differentiation, etc). Infact the harmone receptor complex binds to a specific regulatory site on the chromosome and activates certain genes (DNA) . The activated gene transcribes mRNA which directs the synthesis of proteins and usually enzymes in the cytoplasm. The enzymes promote the metabolic reactions in the cell. The actions of lipid soluble harmones are slower and their effects lastlast longer than the effects of water soluble harmones.



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Answer 2

NCERT based Answer for Class 11 Biology Students

Mechanism of Action of Lipid Soluble Hormones:

 A lipid soluble hormone (a steroid or thyroid hormone) diffuses from blood through plasma membrane into a cell.

 Inside the target cell, the hormone binds with receptor to form hormone–receptor complex.

 Activated hormone–receptor complex enters nucleus and alters gene expression, i.e., it turns a specific gene on or off.  

 As the DNA is transcribed, new mRNA forms, leaves the nucleus and enters cytosol. There it directs synthesis of new proteins (usually enzymes) on the ribosomes.

 New proteins alter cells activity and cause physiological response to that hormone.

 For example, estrogens and progesterone act on uterine wall where they initiate synthesis of proteins which lead to growth of uterine wall. In this way these hormones prepare uterus for pregnancy.  

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