Introduction
Cellular respiration is the process by which cells convert glucose and oxygen into energy, carbon dioxide, and water. It consists of three main steps: glycolysis, the Krebs cycle (also known as the citric acid cycle or tricarboxylic acid cycle), and oxidative phosphorylation. In this article, we will focus on the third step of cellular respiration, oxidative phosphorylation.
Oxidative Phosphorylation
Oxidative phosphorylation is the final step of cellular respiration and takes place in the mitochondria of the cell. It is responsible for producing the majority of ATP, the energy currency of the cell. This step requires oxygen and involves the transfer of electrons from NADH (Nicotinamide Adenine Dinucleotide) and FADH2 (Flavin Adenine Dinucleotide) to oxygen through a series of protein complexes called the electron transport chain.
Electron Transport Chain
The electron transport chain is composed of several protein complexes embedded in the inner mitochondrial membrane. As electrons are passed along the chain, energy is released and used to pump protons (H+) across the membrane, creating a proton gradient. This gradient is essential for the production of ATP.
ATP Synthase
ATP synthase is an enzyme located in the inner mitochondrial membrane. It harnesses the energy from the proton gradient and uses it to convert ADP (adenosine diphosphate) and inorganic phosphate (Pi) into ATP. This process is known as chemiosmosis. Each molecule of NADH produces approximately three ATP molecules, while each molecule of FADH2 produces approximately two ATP molecules.
Role of Oxygen
Oxygen plays a crucial role in oxidative phosphorylation as it serves as the final electron acceptor in the electron transport chain. It combines with electrons and protons at the end of the chain to form water, which is a byproduct of cellular respiration. Without oxygen, oxidative phosphorylation cannot occur, leading to a decrease in ATP production.
Regulation of Oxidative Phosphorylation
Several factors can influence the rate of oxidative phosphorylation. One important regulatory molecule is ADP. As the concentration of ADP increases in the cell, it signals a higher demand for ATP, leading to an increase in oxidative phosphorylation. Conversely, when ATP levels are high, it inhibits the process to prevent an excessive buildup of ATP.
Conclusion
The third step of cellular respiration, oxidative phosphorylation, is a vital process that produces the majority of ATP in the cell. It relies on the electron transport chain, ATP synthase, and oxygen as the final electron acceptor. Understanding this step helps us comprehend the intricate energy production machinery within our cells.
Sources:
1. Alberts, B., Johnson, A., Lewis, J., Morgan, D., Raff, M., Roberts, K., & Walter, P. (2014). Molecular Biology of the Cell. Garland Science.
2. Berg, J. M., Tymoczko, J. L., Gatto, G. J., & Stryer, L. (2015). Biochemistry. W.H. Freeman and Company.