Final answer:
Steroid hormones are synthesized in the smooth endoplasmic reticulum and mitochondria of the cell, and they function by diffusing across the plasma membrane and binding with intracellular receptors in the target cells to influence gene expression.
Step-by-step explanation:
Synthesis of Steroid Hormones
Steroid hormones are synthesized in specific areas within a cell. These hormones are lipid-soluble and are derived from cholesterol, allowing them to readily diffuse across the lipid bilayer of the plasma membrane. The production of steroid hormones occurs in the smooth endoplasmic reticulum (SER) and the mitochondria of the cell. The smooth endoplasmic reticulum is where lipid metabolism and steroid synthesis predominantly take place. After synthesis, steroid hormones leave the cell and travel through the bloodstream, often bound to carrier proteins. Upon reaching their target cells, they diffuse through the cell's plasma membrane due to their hydrophobic nature and bind to intracellular receptors, either in the cytoplasm or directly in the nucleus.
This binding initiates the hormone's action within the target cell, influencing gene expression by forming a hormone-receptor complex that interacts with DNA in the nucleus. The complex serves as a transcription regulator, moderating the synthesis of mRNA and, consequently, the production of specific proteins. This process of gene regulation by steroid hormones is critical in coordinating various physiological functions in the body.