Estrogen receptors (ERs) are a group of proteins found inside cells.
In biology, a gene is a sequence of DNA or RNA that codes for a molecule that has a function.
In the field of molecular biology, nuclear receptors are a class of proteins found within cells that are responsible for sensing steroid and thyroid hormones and certain other molecules.
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, thermo-regulation, waste elimination, and gas exchange via the mother's blood supply; to fight against internal infection; and to produce hormones which support pregnancy.
Steroid hormone receptors are found in the nucleus, cytosol, and also on the plasma membrane of target cells.