FAD

Definition

FAD, or flavin adenine dinucleotide, is a coenzyme involved in various metabolic processes, particularly in the citric acid cycle and electron transport chain. It plays a crucial role in the oxidation-reduction reactions that generate energy through the transfer of electrons. FAD accepts electrons and protons during these metabolic pathways, becoming FADH2, which is essential for ATP production in cellular respiration.

5 Must Know Facts For Your Next Test

1. FAD is reduced to FADH2 during the citric acid cycle when it accepts two electrons and two protons from succinate.
2. FADH2 generated in the citric acid cycle enters the electron transport chain, where it donates electrons to produce ATP.
3. Unlike NADH, which generates three ATP molecules per molecule during oxidative phosphorylation, FADH2 yields only two ATP molecules due to its entry point in the electron transport chain being at a lower energy level.
4. FAD plays a role in several dehydrogenase enzymes that are crucial for metabolism, facilitating the conversion of substrates into energy-rich compounds.
5. Deficiency in riboflavin, which is a precursor to FAD, can lead to various metabolic disorders and impairments in energy production.

Review Questions

• How does FAD function as an electron carrier in the citric acid cycle?
  • FAD acts as an electron carrier in the citric acid cycle by accepting electrons and protons during specific enzymatic reactions. When succinate is oxidized to fumarate, FAD is reduced to FADH2. This conversion is crucial as it allows for the transfer of high-energy electrons into the electron transport chain, ultimately contributing to ATP production through oxidative phosphorylation.
• Discuss the differences between FADH2 and NADH regarding their roles in ATP production during oxidative phosphorylation.
  • FADH2 and NADH both serve as electron carriers but differ in their contributions to ATP production. FADH2 enters the electron transport chain at a lower energy level than NADH, resulting in the production of only two ATP molecules per FADH2 compared to three from NADH. This difference is due to their distinct entry points into the chain and their respective redox potentials, highlighting how efficiently each coenzyme contributes to cellular energy yield.
• Evaluate how deficiencies in riboflavin can impact metabolic processes related to FAD.
  • Deficiencies in riboflavin, which is necessary for the synthesis of FAD, can significantly impair metabolic processes that rely on this coenzyme. Without adequate levels of FAD, reactions catalyzed by flavoproteins become less efficient or may halt entirely. This leads to reduced energy production from carbohydrate and fat metabolism, potentially resulting in fatigue and various metabolic disorders that affect overall health and cellular function.

Related terms

NAD+:

NAD+, or nicotinamide adenine dinucleotide, is another important coenzyme that functions similarly to FAD, serving as an electron carrier in metabolic reactions.

Oxidative phosphorylation:

Oxidative phosphorylation is the process by which ATP is produced using the energy derived from the electron transport chain and the subsequent flow of protons across the mitochondrial membrane.

Citric acid cycle: The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.