binding sites

In biochemistry, a binding site is a region on a protein, DNA, or RNA to which specific other molecules and ions — in this context collectively called  ligands, or more specifically, protein ligands — form a  chemical bond.The term saturation refers to the fraction of total binding sites that are occupied at any given time.When more than one type of ligand can bind to a binding site, competition ensues.
See more at Wikipedia.org...