Question

How many molecules of ATP are produced per molecule of FADH \(_{2}\) oxidized? (a) One (b) Two (c) Three (d) Four

Short answer

(b) Two

Step-by-step solution

Understanding the Question

The question is asking for the number of ATP molecules produced from the oxidation of one molecule of FADH\(_{2}\). In the electron transport chain, each FADH\(_{2}\) molecule is capable of generating two ATP molecules.

Recall ATP Production

Remember that the oxidation process of FADH\(_{2}\) in the electron transport chain results in the production of ATP molecules. Every single FADH\(_{2}\) molecule can generate two ATP molecules when it is oxidized.

Selecting the Correct Answer

Since each molecule of FADH\(_{2}\) generates two ATP molecules when oxidized, the correct answer would be (b) Two.

Key concepts

Electron Transport Chain

Understanding the Electron Transport Chain (ETC) is crucial when studying ATP production in cellular respiration. The ETC consists of a series of protein complexes located in the inner mitochondrial membrane. Electrons from reduced molecules, like NADH and FADH₂, are transferred through these complexes. As electrons move down the chain, energy is released and used to pump protons (H⁺) across the membrane, creating a proton gradient.

This process is vital because it leads to the establishment of an electrochemical gradient known as the proton motive force. FADH₂, which is involved in the question from the exercise, transfers its electrons to complex II in the ETC. This generates less energy compared to NADH because it enters the chain at a later stage. Therefore, for every FADH₂ oxidized, fewer protons are pumped across the membrane, resulting in the production of approximately two ATP molecules.

Oxidative Phosphorylation

The process of Oxidative Phosphorylation is the culmination of energy production in cellular respiration. It includes two main events: the Electron Transport Chain that we discussed earlier, and ATP synthesis facilitated by ATP synthase. This enzyme takes advantage of the proton motive force generated by the ETC. As protons flow back into the mitochondrial matrix down their gradient, ATP synthase synthesizes ATP from ADP and inorganic phosphate.

In the context of FADH₂ oxidation, it is important to note that fewer protons are pumped across the mitochondrial membrane compared to NADH oxidation. This means that when FADH₂ is utilized in the ETC, the proton flow driving ATP synthase results in the production of around two ATP molecules, rather than the three ATP molecules typically associated with the oxidation of NADH.

Cellular Respiration

Cellular Respiration is a vital process for producing energy in the form of ATP in living cells. It can be divided into four stages: glycolysis, the link reaction, the Krebs cycle, and Oxidative Phosphorylation that includes the Electron Transport Chain. During glycolysis and the Krebs cycle, molecules such as NADH and FADH₂ are generated. These molecules are rich in high-energy electrons that are essential for the ETC.

The complete oxidation of glucose in cellular respiration yields a net total of about 30 to 32 ATP molecules per glucose molecule. This includes the ATP produced by substrate-level phosphorylation during earlier stages and Oxidative Phosphorylation. Out of the total ATP produced, each FADH₂ contributes fewer ATP molecules than NADH due to its lower energy yield in the Electron Transport Chain, aligning with the correct solution provided in the exercise.