Hengityskettä

Hengityskettä is a Finnish term that translates to "respiratory chain" or "electron transport chain" in English. This is a series of protein complexes and electron carrier molecules embedded in the inner mitochondrial membrane in eukaryotic cells. Its primary function is to generate a significant portion of the adenosine triphosphate (ATP) used by the cell for energy.

The process begins with electron carriers, primarily NADH and FADH2, which are produced during earlier stages of cellular respiration, such as glycolysis and the Krebs cycle. These molecules donate their high-energy electrons to the first complex in the respiratory chain. As electrons are passed from one complex to the next, they release energy. This energy is used by the protein complexes to pump protons (H+) from the mitochondrial matrix into the intermembrane space.

This pumping action creates an electrochemical gradient, a difference in both charge and concentration of protons across the inner mitochondrial membrane. This gradient represents stored potential energy. Protons then flow back into the mitochondrial matrix down their concentration gradient through a specialized enzyme complex called ATP synthase. The flow of protons through ATP synthase drives the synthesis of ATP from ADP and inorganic phosphate, a process known as oxidative phosphorylation. Oxygen acts as the final electron acceptor at the end of the chain, combining with electrons and protons to form water. The efficiency of the respiratory chain makes it crucial for aerobic organisms.