Cellular respiration is the process by which cells convert glucose into energy in the form of ATP (adenosine triphosphate). The total of 36 ATP molecules produced during this process comes from a series of metabolic pathways, including glycolysis, the citric acid cycle, and oxidative phosphorylation.
Here’s a breakdown:
- Glycolysis: This occurs in the cytoplasm and does not require oxygen. One glucose molecule (6 carbons) is broken down into two molecules of pyruvate (3 carbons). During this process, a net yield of 2 ATP and 2 NADH molecules is produced.
- Citric Acid Cycle (Krebs Cycle): If oxygen is present, the pyruvate enters the mitochondria and is further oxidized in the citric acid cycle. For each glucose molecule, the cycle turns twice (once for each pyruvate), resulting in 2 ATP, 6 NADH, and 2 FADH2.
- Oxidative Phosphorylation: The NADH and FADH2 produced in previous stages are used in the electron transport chain, which occurs in the inner mitochondrial membrane. As electrons move through this chain, they release energy that is used to pump protons (H+) across the membrane, creating a gradient. This process drives ATP synthesis through ATP synthase. This stage can yield approximately 28-34 ATP, depending on the efficiency of the system and the organism.
When you add everything up:
- From glycolysis: 2 ATP
- From the citric acid cycle: 2 ATP
- From oxidative phosphorylation: approximately 28-34 ATP
This gives a total of around 36 ATP, although some estimates suggest that the actual yield may vary based on specific cellular conditions and the transport of NADH into the mitochondria. Overall, cellular respiration is an efficient way for cells to harness energy from glucose, maximizing ATP production.