Flavoproteins are a group of proteins that contain a flavin molecule, which is derived from vitamin B2 (riboflavin). These proteins play essential roles in various biological processes, including cellular respiration and photosynthesis. They are involved in redox reactions, helping to transfer electrons and facilitate energy production in cells. The flavin molecule in flavoproteins can exist in different forms, such as flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Flavoproteins are found in many organisms, from bacteria to humans, and are crucial for the function of enzymes that regulate metabolic pathways and other cellular activities.