FADH2 vs. NADH

Attribute	FADH2	NADH
Chemical Structure	FADH2 has a flavin adenine dinucleotide structure.	NADH has a nicotinamide adenine dinucleotide structure.
Redox Potential	FADH2 has a lower redox potential compared to NADH.	NADH has a higher redox potential compared to FADH2.
Electron Carrier	FADH2 carries electrons to the electron transport chain.	NADH carries electrons to the electron transport chain.
Energy Yield	FADH2 produces 1.5 ATP molecules per molecule.	NADH produces 2.5 ATP molecules per molecule.
Participation in Krebs Cycle	FADH2 participates in the Krebs cycle by donating electrons.	NADH participates in the Krebs cycle by donating electrons.
Coenzyme	FADH2 is a coenzyme derived from riboflavin (vitamin B2).	NADH is a coenzyme derived from niacin (vitamin B3).

Introduction

Cellular respiration is a vital process that occurs in all living organisms, converting nutrients into energy. Two important molecules involved in this process are FADH2 (flavin adenine dinucleotide) and NADH (nicotinamide adenine dinucleotide). Both FADH2 and NADH play crucial roles in the electron transport chain, which is the final step of cellular respiration. In this article, we will explore and compare the attributes of FADH2 and NADH, shedding light on their similarities and differences.

Structure

FADH2 and NADH are both coenzymes that function as electron carriers in cellular respiration. However, they differ in their chemical structures. FADH2 consists of a flavin mononucleotide (FMN) and an adenine nucleotide, while NADH consists of a nicotinamide mononucleotide (NMN) and an adenine nucleotide. The key distinction lies in the presence of a flavin ring in FADH2, which allows it to accept and donate two electrons and two protons, whereas NADH can only accept and donate two electrons and one proton.

Energy Production

Both FADH2 and NADH play crucial roles in the production of ATP (adenosine triphosphate), the energy currency of cells. During cellular respiration, FADH2 and NADH donate their electrons to the electron transport chain, a series of protein complexes embedded in the inner mitochondrial membrane. As electrons pass through the electron transport chain, energy is released and used to pump protons across the membrane, creating an electrochemical gradient. This gradient is then utilized by ATP synthase to produce ATP. However, FADH2 produces less ATP compared to NADH. This is because FADH2 donates its electrons to Complex II of the electron transport chain, bypassing Complex I, resulting in the pumping of fewer protons and thus generating less ATP.

Redox Potential

The redox potential of a molecule refers to its tendency to donate or accept electrons. FADH2 and NADH have different redox potentials, which influence their roles in cellular respiration. FADH2 has a lower redox potential compared to NADH, making it a stronger electron donor. This means that FADH2 is more likely to donate its electrons to the electron transport chain, while NADH is more likely to accept electrons from other molecules. The difference in redox potential allows for the efficient flow of electrons through the electron transport chain, ensuring the production of ATP.

Production in Cellular Respiration

FADH2 and NADH are produced at different stages of cellular respiration. NADH is primarily generated during glycolysis, the citric acid cycle (also known as the Krebs cycle), and the conversion of pyruvate to acetyl-CoA. In contrast, FADH2 is mainly produced during the citric acid cycle. During glycolysis, glucose is broken down into pyruvate, generating a small amount of NADH. In the citric acid cycle, NAD+ is reduced to NADH multiple times, resulting in the production of a significant amount of NADH. FADH2 is formed when succinate is oxidized to fumarate in the citric acid cycle. Therefore, the production of FADH2 and NADH is interconnected but occurs at different stages of cellular respiration.

Role in Oxidative Phosphorylation

Oxidative phosphorylation is the process by which ATP is synthesized using the energy released during the electron transport chain. Both FADH2 and NADH play crucial roles in this process. NADH donates its electrons to Complex I of the electron transport chain, while FADH2 donates its electrons to Complex II. The electrons are then passed through a series of protein complexes, ultimately leading to the pumping of protons and the generation of ATP. However, since NADH donates its electrons to Complex I, it contributes to the pumping of more protons compared to FADH2, resulting in the production of more ATP. This highlights the importance of NADH in oxidative phosphorylation.

Other Functions

Besides their roles in cellular respiration, FADH2 and NADH have additional functions in various metabolic pathways. FADH2 is involved in other redox reactions, such as those occurring in fatty acid oxidation and the metabolism of certain amino acids. It acts as a cofactor for enzymes involved in these processes, facilitating the transfer of electrons. NADH, on the other hand, participates in numerous enzymatic reactions, serving as a cofactor for dehydrogenase enzymes. These enzymes are responsible for the transfer of hydrogen atoms and electrons in various metabolic pathways, including the breakdown of carbohydrates, fats, and proteins.

Conclusion

In conclusion, FADH2 and NADH are essential molecules in cellular respiration, serving as electron carriers in the electron transport chain. While they share similarities in their roles and functions, they also possess distinct attributes. FADH2 has a flavin ring, donates two electrons and two protons, and has a lower redox potential. NADH, on the other hand, lacks a flavin ring, donates two electrons and one proton, and has a higher redox potential. Additionally, NADH produces more ATP compared to FADH2 due to its involvement in Complex I of the electron transport chain. Understanding the attributes of FADH2 and NADH provides insights into the intricacies of cellular respiration and the efficient production of energy in living organisms.