What Are the Functions of Coenzymes?

Coenzymes are essential organic compounds that attach to enzymes to help them catalyze reactions. An enzyme has an active site where it catalyzes the reaction of a substrate, but a coenzyme binds to other areas of the enzyme, changing its shape and allowing the active site to better fit the substrate. Many of the coenzymes in our diet are essential vitamins we need to carry out reactions for cell function. The function of the coenzyme is to bring an added element to the reaction such as an electron or functional group.

NAD

• Nicotine adenine dinucleotide (NAD) is an electron carrier. It provides hydride ions for a number of oxidation-reduction reactions. The ring structure functions as an electron sink, carrying elections to and from locations in the cell. NAD also functions in metabolism by collection electrons during catabolism and donating electrons during anabolism.

Coenzyme Q

• CoQ is another electron carrier that is lipid soluble. It exists in the membrane of the cell, carrying electrons through the electron transport chain in the creation of adenosine triphosphate (ATP). CoQ acts as a bridge between the proteins in the mitochondria, carrying electrons from complexes one and three and two and three. NAD, in its reduced form, nicotine adenine dinucleotide hydrogen (NADH), provides the electrons for CoQ's function.

Coenzyme A

• CoA is an essential coenzyme that functions as a two carbon carrier, more commonly known as the acetyl group carrier. CoA is similar to NAD and flavin adenine dinucleotide (FAD) in structure, but the acetyl group is attached by a thiol ester bond. CoA is the starting point in the citric acid cycle in the mitochondria where ATP is created. It's also important in the breakdown of fatty acids.

FAD

• FAD is also similar in structure to NAD, but it has different functions. FAD also performs reactions as flavin mononucleotide (FMN), and it contains riboflavin, adenine, ribose and phosphates. FMN also functions in the electron transport chain in complex one. It acts as an oxidizing agent, taking electrons from NADH to move through the process.

Biotin

• Biotin is an essential coenzyme, but it can only be synthesized by few organisms like bacteria, yeasts and molds. Biotin is a carboxylase carrier providing the functional group for catalysis. It also functions in many reactions involving DNA such as histone interaction, helping DNA relax for replication and transcription activity.