1. Glycolysis:
- Glycolysis takes place in the cytoplasm of the cell. It is the initial stage of cellular respiration and does not require oxygen.
- One molecule of glucose, a six-carbon sugar, is broken down into two molecules of pyruvate, a three-carbon compound.
- During this process, a small amount of ATP is produced (2 molecules per glucose), and carrier molecules NADH (nicotinamide adenine dinucleotide) and FADH2 (flavin adenine dinucleotide) are generated, which contain high-energy electrons essential for ATP production later in the process.
2. The Krebs Cycle:
- The Krebs cycle occurs in the mitochondria of the cell and operates only in the presence of oxygen.
- Each pyruvate molecule produced during glycolysis enters the mitochondria and undergoes a series of nine chemical reactions.
- During these reactions, carbon atoms from the pyruvate molecules are released as carbon dioxide (CO2), while the energy released is captured to form ATP (up to 2 molecules per pyruvate), NADH (3 molecules per pyruvate), and FADH2 (2 molecules per pyruvate).
3. Oxidative Phosphorylation:
- Oxidative phosphorylation takes place in the inner membrane of the mitochondria and involves a series of electron transfers.
- The NADH and FADH2 molecules generated in glycolysis and the Krebs cycle pass their high-energy electrons to a chain of electron carriers.
- As the electrons move through this chain, a process called chemiosmosis occurs, where protons (H+) are pumped from the mitochondrial matrix into the intermembrane space.
- The flow of protons back into the matrix through a membrane protein called ATP synthase drives the synthesis of ATP. One ATP molecule is produced for every three protons that move back in.
Through cellular respiration, our bodies efficiently extract energy stored in organic molecules and convert it into ATP, which is utilized by nearly every cellular function that requires energy. This process ensures a constant supply of energy to power the various activities and processes within our cells.
