If oxygen is present, sugar molecules metabolize by going through:
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If oxygen is present, sugar molecules metabolize through a process called aerobic respiration. Aerobic respiration occurs in the mitochondria of cells and involves several steps. Here's how sugar molecules are metabolized in the presence of oxygen:
1. Glycolysis: The sugar molecule, usually glucose, is broken down into two molecules of pyruvate. This process occurs in the cytoplasm of the cell and does not require oxygen.
2. Transition reaction: The pyruvate molecules are transported into the mitochondria, where they undergo a transition reaction. This reaction converts each pyruvate molecule into a molecule called acetyl CoA, releasing one molecule of carbon dioxide in the process. The transition reaction requires oxygen as it takes place within the mitochondria.
3. Citric acid cycle (Krebs cycle): The acetyl CoA molecules enter the citric acid cycle, which occurs in the mitochondria. In this cycle, the acetyl CoA is broken down further, releasing energy and generating high-energy molecules like NADH and FADH2. Carbon dioxide is also produced as a byproduct.
4. Electron transport chain: The high-energy molecules NADH and FADH2 generated in the citric acid cycle carry electrons to the electron transport chain, which is embedded in the inner membrane of the mitochondria. These electrons move along the chain, releasing energy that is used to generate ATP, the main energy currency of cells. The oxygen molecules act as the final electron acceptor in this process.
In summary, when oxygen is present, sugar molecules go through glycolysis, the transition reaction, the citric acid cycle, and the electron transport chain, ultimately resulting in the complete oxidation of the sugar and the generation of ATP.