Pan-African flag - History. 1  The flag was created in 1920 by members of UNIA in response to the enormously popular 1900 coon song Every Race Has a Flag but the Coon. [4] which has been cited as one of the three songs that firmly established the term coon in the American vocabulary.
A ligand is any molecule that binds to a specific site on a protein or other molecule. In this case, the estrogen hormone 17-beta-estradiol is the ligand, and the estrogen receptor is the protein. Binding turns on, or activates, a hormone receptor.
A receptor is basically a protein in a cell (usually in a cell membrane, but doesn't have to be (eg. NO and steroid receptors). When a ligand (an agonist) meets the receptor, the protein changes its physical conformation, making it more or less likely to do something else, eg. catalyze something, open an ion channel. Antagonists bind to receptors like agonists, but without doing anything, effectively blocking them.