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.
1 Binding of the signal molecule to the receptor protein will activate intracellular signaling proteins that initiate a signaling cascade. 2  Target proteins: the conformations or other properties of the target proteins are altered when a signaling pathway is active and changes the behavior of the cell. protein-coupled receptors comprise a large protein family of transmembrane receptors. They are found only in eukaryotes. The ligands which bind and activate these receptors include: photosensitive compounds, odors, pheromones, hormones, and neurotransmitters.