Final answer:
Steroid hormones bind to intracellular receptors to form a complex that acts as a transcription factor, influencing the transcription of specific genes and subsequent protein synthesis.
Step-by-step explanation:
When steroid hormones act on a cell nucleus, the hormone-receptor complex acts as a transcription factor, binds to DNA, and activates one or more genes, which create mRNA to direct the synthesis of new proteins.
Steroid hormones, such as testosterone, estrogens, and glucocorticoids, cross the cell membrane to exert their effects. They bind to steroid hormone receptors either in the cytoplasm or directly within the nucleus. Once the hormone has bound to its receptor, the newly formed complex moves to the DNA and attaches itself to specific response elements, which are DNA sequences that regulate transcription. This hormone-receptor complex essentially acts as a switch, turning genes on or off, thus determining the level of mRNA and subsequent protein synthesis.
These events lead to changes in the cell's activity, either by altering its structure or by influencing the enzymatic reactions within the cell. For example, the glucocorticoid receptor is a zinc-finger transcription factor that binds to a palindromic sequence on the DNA, which then influences gene transcription.