Difference Between NAD and FAD

Coenzymes are essential for carrying out different reactions in our bodies. Coenzymes can be considered helper molecules that help in chemical reactions.


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Key Takeaways

  1. NAD (nicotinamide adenine dinucleotide) is a coenzyme that acts as an electron carrier in metabolic reactions, while FAD (flavin adenine dinucleotide) is another coenzyme that carries electrons in redox reactions.
  2. NAD is involved in energy metabolism and is used in both catabolic and anabolic reactions, while FAD is involved in oxidative reactions in the mitochondria.
  3. NAD is derived from niacin (vitamin B3), while FAD is derived from riboflavin (vitamin B2).


NAD and FAD differ because NAD can accept only one hydrogen atom, whereas FAD can accept two hydrogen atoms. NAD means Nicotinamide adenine dinucleotide, and FAD means Flavin adenine dinucleotide. Both different roles to play NAD is a coenzyme found in all living beings, whereas FAD is a cofactor that helps in many metabolic and complex reactions.


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It is found in all the cells which are living. As the name dinucleotide suggests, it has two nucleotides joined by phosphate groups. NAD can be found in two forms, i.e., oxidized and reduced condition or state.

FAD is Flavin adenine dinucleotide, a cofactor that is the type of coenzyme, and it is involved in various enzymatic reactions that are necessary for metabolism.

Comparison Table

Parameters of ComparisonNADFAD
Full formNAD  is Nicotinamide adenine dinucleotide.FAD is Flavin adenine dinucleotide.
DefinitionNAD is a coenzyme that can be found in living cells.FAD is a redox cofactor involved in many metabolic and complex reactions.
ProductionIt is produced during glycolysis and the Krebs cycle.It is only produced during the Krebs cycle.
HydrogenIt accepts only one9 hydrogen atom.It can accept two hydrogen atoms.
Electron TransferIt transfers its electron to Cytochrome Complex 1 and gives 3 ATP.It transfers its electron to Cytochrome Complex 2 and gives 2 ATP.

What is NAD?

 Nicotinamide adenine dinucleotide, also known as NAD, consists of two nucleotides joined together by a phosphate group.

Apart from electron transfer, it also helps in the cellular process, such as acting as a catalyst or reagent of enzymes or adding and subtracting chemical groups from the protein itself. NAD and its enzymes are so important that it becomes very vital in drug discovery.

It has a molar mass of 663.43g/molecule. Its melting point is 60 °C (320 °F; 433 K). It looks like a white powder whether it is in any state and is hygroscopic and water-soluble(highly) in nature.


What is FAD?

Flavin adenine dinucleotide, also known by the name FAD is very vital in the field of biochemistry. It is a redox-active coenzyme that is associated with different types of protein. It has four states in which it can exist: quinone, semiquinone,flavin-N(5)-oxide, and hydroquinone.

Like NAD, FAD also has two parts: the adenine nucleotide and the flavin mononucleotide (FMN) bonded together by phosphate groups. FAD can be reduced to form FADH2 by accepting two hydrogens and two electrons.

In different states, FAD has different colors. Like in a super oxidized state, it turns yellow-orange. In the fully oxidized state, it is yellow. In the half-reduced form, it is either red or blue-like pH; if reduced fully, it becomes colorless.


Main Differences Between NAD and FAD

  1. NAD accepts only one hydrogen atom. FAD can accept two hydrogen atoms.
  2. NAD transfers its electron to Cytochrome Complex 1, giving 3 ATP for each NADH produced. FAD transfers its electron to Cytochrome Complex 2, giving 2 ATP for each FDH2 produced.
  1. https://pubs.acs.org/doi/abs/10.1021/bi002061f
  2. https://academic.oup.com/nar/article-abstract/31/3/e8/1130007

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