- In biology, the term “FAD” stands for “Flavin Adenine Dinucleotide.
- It is derived from riboflavin (vitamin B2) and is an essential component of several enzymes.
| Functions | Description |
| Role as an electron carrier | · FAD serves as an electron carrier in the process of cellular respiration and · It transfers the electrons to the electron transport chain. |
| Role in feedback Regulation of Krebs cycle | · FAD is involved in feedback regulation by influencing the rate of cycle based on the energy requirements of the cell. |
| Role in Citric acid cycle | · It is a cofactor in enzymes like succinate dehydrogenase, which participates in the citric acid cycle (Krebs cycle) · Helps in the production of ATP and CO2. |
| Role in the oxidation of Fatty Acids | · FAD assists in the breakdown of fatty acids into acetyl-CoA, which can be used for energy production. |
Different forms of FAD:
| Forms | FAD | FADH• | FADH2 |
| State | · Oxidized | · Partially reduced | · Reduced |
| Structure | · Dinucleotide coenzyme with two adenine bases, a ribose sugar, and a flavin mononucleotide (FMN) unit | · One unpaired electron on the flavin mononucleotide (FMNH) unit. | · Dinucleotide coenzyme with one additional hydrogen atom on the flavin mononucleotide (FMNH) unit. |
| Function | · Acts as an electron acceptor | · Can participate in electron transfer reactions. · An unstable radical species. | · Acts as an electron donor to form FAD. · Serves as a temporary electron carrier in cellular respiration. |
Comparison between FAD and NAD
| Aspect | FAD | NAD |
| Full form | · Flavin Adenine Dinucleotide | · Nicotinamide Adenine Dinucleotide |
| Discoverer | · Hugo Theorell | · Sir Arthur Harden and William John Young |
| Year of discovery | · 1937 (Structure) · 1949 (As a coenzyme) | · 1906-1907 |
| Derived from | · Riboflavin vitamin B2 | · Nicotinamide vitamin B3 |
| Coenzyme Type | · Flavoprotein – contains flavin as a prosthetic group. | · Dinucleotide coenzyme – contains nicotinamid as a prosthetic group. |
| Structural formula | ||
| Molar mass | · 785.5497 g/mol | · 663.43 g/mol |
| Forms | · FAD (oxidized form) · FADH2 (reduced form) | · NAD+ (oxidized form) · NADH (reduced form) |
| Color | · Yellow (oxidized) · Colorless (reduced) | · Colorless (NAD+) · Light blue (NADH) |
| Redox Reactions | · Accepts 2 electrons and 2 protons in reduction. · Donates 2 electrons and 2 protons in oxidation. | · Accepts 2 electrons and 1 proton in reduction. · Donates 2 electrons and 1 proton in oxidation. |
| Cellular Processes | · Involved in the citric acid cycle (Krebs cycle) · fatty acid oxidation · Electron transport chain | · Participates in glycolysis · the citric acid Cycle · electron transport chain during cellular respiration · Other metabolic pathways |
Comparison between FAD and FADH:
| Aspect | FAD | FADH |
| Role in Electron Transfer | · Accepts two electrons and two protons in reduction reactions to become FADH2 | · Donates two electrons and two protons in oxidation reactions to become FAD |
| Color | · Yellow in its oxidized form | · Colorless or pale yellow in its reduced form |
| Energy Level | · Energy in the molecule is lower | · Energy in the molecule is high |
| Function | · Acts as an electron carrier, accepting and donating electrons in redox reactions | · Functions as a temporary electron carrier, donating electrons to the electron transport chain for ATP synthesis |
| Type of coenzyme | · Flavoprotein – contains flavin as a prosthetic group | · Flavoprotein – contains flavin as a prosthetic group |
| Stability | · Stable | · Less stable |
| Involvement in Cellular Processes | · Participates in the citric acid cycle (Krebs cycle) · Fatty acid oxidation · Electron transfer reactions in the mitochondrial respiratory chain | · Involved in the electron transport chain during cellular respiration · Contributing to oxidative phosphorylation and ATP production |