In mitochondrial electron transport, what is the direct role of O2?
A: To provide the driving force for the synthesis of ATP from ADP and Pi.
B: To function as the final electron acceptor in the electron transport chain.
C: To oxidize NADH and FADH2 from glycolysis, acetyl CoA formation, and the citric acid cycle.
D: To provide the driving force for the production of a proton gradient.
The correct answer is option B. “To function as the final electron acceptor in the electron transport chain.”
In mitochondrial electron transport, the direct role of O2 is to function as the final electron acceptor in the electron transport chain.
To understand the direct role of O2, first, we need to understand the electron transport chain and the process of cellular respiration.
The electron transport chain:
“The electron transport chain is a mitochondrial pathway in which electrons move across a redox span of 1.1 V from NAD+/NADH to O2/H2O”(K. Asha 2018).
In this chain, three complexes are involved, which are; complex I, complex III, and complex IV.
Those compounds which have more positive redox potential than NADH +NAD, such as succinate, can transfer electrons through different complex (complex II).
When O2 reacts with electrons, it produces water. O2 will take the low energy ones that come out of the ETC. It keeps the electron particles from backing up through the ETC, allowing energy formation continuously.
When O2 is absent, electron flow is not sustainable, and only fermentation can occur, which produces harmful by-products like lactic acid or ethanol by providing massive energy.
The process in which cells degrade food molecules to get energy in Adenosine Triphosphate (ATP) form, is called cellular respiration.
Respiration is composed of the following steps:
- Glycolysis; oxidation of glucose to pyruvate.
- Acetyl-CoA formation.
- Krebs cycle.
- Electron transport chain and oxidative phosphorylation.
- Glucose oxidation reduces NAD+ to FAD+ to FADH and NADH. When glucose is oxidized, these molecules accept the produced electrons.
- The electrons accepted by FADH and NADH pass via a series of electron transporters, moving from a high energy level to a lower one.
- Finally, oxygen (which is the last electron acceptor) combines with 2 protons (hydrogen ions) and produces water.