Question

Give an example of a specific intracellular receptor be sure to indicate its exact location and function. Please give as much details as you can for me to understand it.

Thank you.

Answer 1

1-Several hormones,for eg.adrenal and gonadal steroid hormones,thyroid hormones,retinoid hormones,and vit D ,bind with protein receptors inside the cell rather than in the cell membrane.

2-As these hormones are lipid soluble,they easily cross the cell membrane and interact with receptors in cytoplasm or nucleus.

3-The activated hormone-receptor complex binds with a specific regulatory sequence of DNA called the hormone response element,and in this manner either activated or repress transcription of specific genes and formation of messenger RNA,as the result newly formed proteins appear in cell and become the controller's of new or altered cellular functions.

4-Responses of different tissues to a hormone are determined not only by specificity of receptors but also by expression of genes that the receptor regulates.

​​​​​​Example:

Thyroid hormone:It activates nuclear receptors.

The thyroid hormones receptors are either attached to DNA genetic strands or located in proximity to them.On binding with thyroid hormone,the receptors become activated and initiate the transcription process.Then a large numbers of different types of mRNA are formed, followed by RNA translation on cytoplasmic ribosomes to form hundreds of new intracellular proteins,which cause most of the effects of thyroid hormones.

Mechanism of action of thyroid hormone through intracellular receptor:

1-Thyroid hormones(T4 and T3) enter the cell membrane by a carrier- mediated adenosine triphosphate-dependent transport process.

2-Much of the T4 is deiodonated to form T3 , which interacts with the thyroid hormone receptor,bound as a heterodimer with a retinoid X receptor,of the thyroid hormone response element of the gene.

3-This action causes either increase or decrease in transcription of genes that leads to formation of proteins,thus producing the thyroid hormone response of the cell.