Balance of the respiratory chain
The decisive end product of the respiratory chain is the ATP (adenine triphosphate), which is a universal energy source of the body. ATP is synthesized with the help of a proton gradient that is formed during the respiratory chain. NADH+H+ and FADH2 have different efficiency.
NADH+H+ is oxidized back to NAD+ at the first enzyme complex on the respiratory chain, pumping a total of 10 protons into the intermembrane space. The oxidation of FADH2 has a lower yield because only 6 protons are transported into the intermembrane space. This is due to the fact that FADH2 is introduced into the respiratory chain at the second enzyme complex, thus bypassing the first complex.
In order to synthesise ATP, 4 protons must flow through the fifth complex. Consequently, 2.5 ATP (10/4=2.5) is produced per NADH+H+ and 1.5 ATP (6/4=1.5) per FADH2. When a sugar molecule is degraded via glycolysis, citrate cycle and respiratory chain, a maximum of 32 ATP can be generated in this way, which are available to the organism.
What role do the mitochondria play?
Mitochondria are cell organelles that occur in animal and plant organisms. Various energy processes take place in mitochondria, including the respiratory chain. Since the respiratory chain is the decisive process for energy production, mitochondria are also called the “power stations of the cell”.
They have a double membrane so that a total of two separate reaction chambers are created. Inside is the matrix space and between the two membranes the intermembrane space. These two spaces are fundamental for the course of the respiratory chain. Only in this way can a proton gradient be established, which is important for ATP synthesis.
What does cyanide do in the respiratory chain?
Cyanides are dangerous poisonous substances, which include compounds of prussic acid. They are able to bring the respiratory chain to a standstill. In concrete terms, cyanide binds to the iron of the fourth complex of the respiratory chain.
Consequently, the electrons can no longer be transferred to molecular oxygen. The entire respiratory chain can therefore no longer run off. The consequence is a lack of the energy carrier ATP (adenosine triphosphate) and a so-called “internal suffocation” occurs. The symptoms such as vomiting, unconsciousness and cramps occur very quickly after cyanide poisoning and lead to rapid death if left untreated.
What is a respiratory chain defect?
A respiratory chain defect is a rare metabolic disease that often manifests itself in childhood. It is caused by changes in the genetic information (DNA). The mitochondria are restricted in their function and the respiratory chain does not function properly.
This is particularly noticeable in organs that consume a lot of energy in the form of ATP (adenosine triphosphate). A typical symptom is therefore muscle pain or muscle weakness. A therapy for this disease is difficult to find, as it is a hereditary disease.
Care should be taken to ensure a sufficient energy supply (e.g. through glucose). Otherwise a purely symptomatic treatment is appropriate.