What hormones depend on a one-messenger model of hormonal control? How does this model operate? What is the end target of most of these hormones within the cell?
Thyroxin and the steroidal hormones depend on a one-messenger model of hormonal control. Thyroxin enters target cells directly and alters the genes in the nucleus and mitochondrial enzyme activity to exact its effect on target cells. The steroidal hormones, being lipid-soluble, also penetrate the plasma membrane and cytoplasm of their target cells. In the cytoplasm, steroidal hormones bind with specific receptor molecules and move into the nucleus where they influence the transcription of RNA and, thus, influence what proteins, especially what enzymes, the cell produces.
