Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase.
Flavin adenine dinucleotide consists of two main portions: an adenine nucleotide (adenosine monophosphate) and a flavin mononucleotide bridged together through their phosphate groups. Adenine is bound to a cyclic ribose at the 1' carbon, while phosphate is bound to the ribose at the 5' carbon to form the adenine nucleotide. Riboflavin is formed by a carbon-nitrogen (C-N) bond between a isoalloxazine and a ribitol.
Therefore, the correct answer is option A.