Q. How in the respiratory chain do electrons from NADH2 and FADH2 passing through cytochromes liberate energy for the ATP synthesis? What is this ATP synthesis called?
NADH2and FADH2 oxidate into NAD and FAD and liberate hydrogen ions and highly energized electrons in the beginning of the respiratory chain.
The energy lost by electrons that pass through the cytochromes is used to pump protons hydrogen ions out of the inner mitochondrial membrane to the region between the inner and the outer membranes of the mitochondrion. Hydrogen concentration gradient between the internal and the outer spaces delimited by the inner membrane forces protons hydrogen ions to return to the mitochondrial matrix the region inside the internal membrane however that return is only possible if hydrogen ions pass through an enzymatic complex called ATP synthetase embedded in the inner membrane. In that passage the ATP synthetase phosphorylates ATP and then ADP molecules are produced.
Hydrogen liberated in the mitochondrion then combines with oxygen to form water As a reaction that depends on oxygen this kind of ATP synthesis is called oxidative phosphorylation.