A hormone receptor is a protein complex through which hormones interact with cells. Hormones use their receptors to regulate whether a protein is produced or not, and to control the amount of a protein that is made. Some receptors are located in the cell membrane and interact with genes indirectly through chemical signals, while others are near the nucleus and control the expression of DNA directly. Inside the cell, a hormone receptor is activated by forming a complex with a steroid molecule.
A hormone receptor is composed of protein molecules embedded in the membrane of a cell or located inside it. Since they can pass through the lipid membranes that make up the exterior of cells, hormones may bind to receptors that are well inside the cytoplasm. Unlike many other biological signaling molecules, hormones do not have to rely on multiple chemical pathways to relay their message to the organelles inside the cell. Due to this flexibility, a hormone receptor can be located in many different cellular locations.
A peptide hormone receptor is a protein located in the cell's lipid membrane. There are different types of peptide receptors, also called cell surface receptors. They are categorized according to how they signal activity in the cell.
Many depend on second messengers like G-proteins to communicate with the cell interior, since peptide hormones cannot cross into the cytoplasm. Steroid hormone receptors, conversely, function by inhibiting or activating genes inside of the cell's nucleus. They respond to a wide range of steroids including thyroid and sex hormones and cortisol, typically taking more time to work than peptide receptors do.
Steroid hormones cross the plasma membrane and bind to receptors in the nucleus of the cell. They form a hormone receptor complex that directly interacts with DNA, regulating whether or not certain genes are transcribed into RNA. This controls protein expression. The products of this primary response may themselves be used as further signals that regulate expression of genes, binding to a different set of hormone receptors in the process. Steroids can thus have wide-ranging effects on a number of genes even if only one initial hormone-receptor complex is formed.
Since some steroids can be quite similar bioechemically, hormone receptors have mechanisms to ensure that one hormone does not intrude on the pathway of another, and trigger serious or even lethal changes in the body. While each steroid receptor has a greater response to its primary hormone, it may be capable of binding another chemically similar one. As a safeguard, some receptors have enzymes that will block all but their preferred hormone. Some diseases can interfere with selectivity or inhibit a hormone receptor's responsiveness.