Inside the mitochondrion, a complex set of biochemical processes occur primarily to generate energy in the form of ATP (adenosine triphosphate), which is the main energy currency of the cell. The mitochondrion is often called the "powerhouse of the cell" because of this vital function.
Main Processes Inside the Mitochondrion
- Citric Acid Cycle (Krebs Cycle): In the matrix of the mitochondrion, the pyruvate produced from glucose breakdown is converted into acetyl-CoA, which then enters the citric acid cycle. This cycle produces high-energy electron carriers NADH and FADH2, along with small amounts of ATP and carbon dioxide as a byproduct.
- Electron Transport Chain and Oxidative Phosphorylation: The inner mitochondrial membrane contains protein complexes that form the electron transport chain (ETC). NADH and FADH2 deliver electrons to this chain, which transfers the electrons through complexes I to IV. This electron transfer pumps protons from the matrix into the intermembrane space, creating an electrochemical gradient.
- ATP Synthesis: Protons flow back into the matrix through ATP synthase, a protein complex that uses this proton motive force to generate ATP from ADP and inorganic phosphate. This process is called oxidative phosphorylation and produces the majority of ATP in aerobic respiration.
- Other Functions: Besides energy production, mitochondria also regulate calcium storage, participate in signaling pathways, control cell death (apoptosis), and maintain their own DNA and protein synthesis for function and replication.
Thus, mitochondria convert chemical energy from nutrients into ATP through interconnected cycles and membrane processes, balancing energy production and cellular health maintenance.