Views: 3 Author: Site Editor Publish Time: 2022-07-18 Origin: Site
Because raw steroid powders are small in size (molecular weight is only about 300) and fat-soluble, they can enter cells through cell membranes.
After entering the cell, it affects the gene surface through two steps to play its role, so this mechanism of action is called the two-step action principle, or the gene expression theory.
The first step is the binding of hormones to cytoplasmic receptors to form hormone-cytoplasmic receptor complexes.
There are raw steroid powders hormone receptors in target cells, they are proteins, and they are characterized by strong specificity and high affinity for binding with corresponding hormones.
For example, estradiol receptors in the cytoplasm of uterine tissue can bind 17β-estradiol but not 17α-estradiol.
The affinity of hormones and receptors is parallel to the strength of hormones. Moreover, the content of cytoplasmic receptors also changes with the functional status of target organs.
When the hormone enters the cell and binds to the cytoplasmic receptor, the receptor protein undergoes a conformational change, so that the hormone-cytoplasmic receptor complex acquires the ability to enter the nucleus and transfer from the cytoplasm to the nucleus.
The second step is to combine with nuclear receptors to form hormone-nuclear receptor complexes, thereby stimulating the transcription process of DNA, generating new mRNA, inducing protein synthesis, and causing corresponding biological effects.
In recent years, due to the development and application of genetic engineering technology, the structure of many nuclear receptors for steroid hormones has been clear.
They are proteins that specifically regulate transcription, and their activity is controlled by raw steroid powders.
Nuclear receptors mainly have three functional domains: hormone binding domain, DNAA domain and transcription enhancing domain.
Once the hormone binds to the receptor, the molecular conformation of the receptor changes, exposing the DNA-binding domain and the transcription-enhancing domain that are hidden inside the molecule, so that the receptor DNA binds, thereby producing the effect of enhancing transcription.
In addition, the experimental data of politicians show that there may be a specific sequence of amino acids in the DNA binding domain, which plays a role in mediating the binding of hormone receptor complexes to specific sites in chromatin, play the role of nuclear localization signal.
Although thyroid hormone is a nitrogen-containing hormone, its mechanism of action is similar to that of raw steroid powders.
It can enter cells, but enter the nucleus without binding to cytoplasmic receptors, and bind to nuclear receptors to regulate gene expression.
It should be pointed out that nitrogen-containing hormones can act on transcription and translation stages to affect protein synthesis; conversely, steroid hormones can also act on cell membranes to cause a phenomenon that is difficult to explain by gene expression theory.