text: <unk>  is a tricyclic heteronuclear organic ring based on pteridine whose biochemical source is the vitamin riboflavin. The<unk>  moiety is often attached with an adenosine diphosphate to form<unk>  adenine dinucleotide (FAD), and in other circumstances, is found as<unk>  mononucleotide (or FMN), a phosphorylated form of riboflavin. It is in one or the other of these forms that<unk>  is present as a prosthetic group in flavoproteins.
  The<unk>  group is capable of undergoing oxidation-reduction reactions, and can accept either one electron in a two step process or can accept two electrons at once. In the form of FADH2, it is one of the cofactors that can transfer electrons to the electron transfer chain.
option_0: Flavin
option_1: Coenzyme
option_2: Chlorophyll
option_3: Hydroquinone
option_4: Biotin
option_5: Glycobiarsol
option_6: Hemin
option_7: Heme