ATP is primarily produced through the process of cellular respiration, which includes glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation. In glycolysis, glucose is broken down into pyruvate, producing a small amount of ATP. The citric acid cycle further oxidizes products to generate electron carriers NADH and FADH2, which then transfer electrons to the electron transport chain in the mitochondria. This electron transport chain creates a proton gradient that drives ATP synthesis via the enzyme ATP synthase, producing the majority of ATP molecules. ATP can also be produced anaerobically via fermentation processes when oxygen is scarce. Additionally, ATP production occurs from the beta-oxidation of fatty acids and the catabolism of ketone bodies, which feed into the citric acid cycle and electron transport chain, contributing further to ATP synthesis. In plants, ATP can also be produced through photophosphorylation during photosynthesis, where light energy is used to drive proton pumping and ATP synthase activation. Thus, the main biological processes of ATP production are:
- Glycolysis
- Citric acid cycle (Krebs cycle)
- Oxidative phosphorylation via the electron transport chain
- Beta-oxidation of fatty acids
- Anaerobic fermentation (in absence of oxygen)
- Photophosphorylation (in plants).
