Each stage of aerobic respiration involves a series of coupled reactions that release energy in a usable form. Here is a brief overview of the coupled reactions:
1. Glycolysis:
- Glucose is broken down into two molecules of pyruvate.
- Each molecule of glucose provides two net molecules of ATP (adenosine triphosphate) through substrate-level phosphorylation.
- Two molecules of NADH (nicotinamide adenine dinucleotide) are produced, each carrying two high-energy electrons.
2. Krebs Cycle:
- Each molecule of pyruvate from glycolysis enters the Krebs cycle.
- Over multiple enzymatic steps, the acetyl group from pyruvate is oxidized to produce CO2 and generate ATP, NADH, and FADH2 (flavin adenine dinucleotide).
- For every turn of the Krebs cycle, three molecules of NADH, two molecules of FADH2, and two molecules of ATP are produced.
3. Oxidative Phosphorylation:
- NADH and FADH2 molecules from glycolysis and the Krebs cycle donate their high-energy electrons to the electron transport chain (ETC).
- The ETC is a series of membrane-bound protein complexes that facilitate the transfer of electrons from NADH and FADH2 to oxygen.
- As electrons move through the ETC, their energy is used to pump hydrogen ions (H+) across the mitochondrial membrane, creating a proton gradient.
- The proton gradient drives the synthesis of ATP through a final enzyme called ATP synthase.
In summary, aerobic respiration involves coupled reactions in glycolysis, the Krebs cycle, and oxidative phosphorylation. Each stage is interconnected, and the energy released from glucose breakdown is captured and stored as ATP molecules, which are the cellular currency for energy transfer. This process allows cells to efficiently harness the energy stored in organic molecules and convert it into a usable form for various cellular activities.
