Glycolysis is the first step in cellular respiration, occurring in the cytoplasm of the cell. During this process, one molecule of glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (three-carbon compounds), resulting in a net gain of two ATP molecules and two NADH molecules for energy storage. The process involves a series of enzymatic reactions that also utilize two molecules of ATP to initiate the breakdown, creating energy-rich intermediates along the way.
The Krebs Cycle, also known as the citric acid cycle, takes place in the mitochondria and follows glycolysis. In this cycle, each pyruvate is converted into acetyl-CoA before entering the cycle, where it combines with oxaloacetate to form citric acid, which undergoes a series of transformations. As the cycle progresses, it releases carbon dioxide as a waste product and regenerates oxaloacetate, while producing two ATP (or GTP), several NADH, and FADHâ‚‚ which are crucial for the next step in cellular respiration.
The Electron Transport Chain (ETC) is the final step and occurs in the inner mitochondrial membrane, where the NADH and FADHâ‚‚ generated from glycolysis and the Krebs cycle donate electrons. As the electrons are transferred through a series of protein complexes, energy is released and used to pump protons across the membrane, creating a proton gradient. This gradient drives ATP synthesis through ATP synthase, as protons flow back into the mitochondrial matrix, and ultimately, oxygen serves as the final electron acceptor, forming water as a byproduct.