The functional groups of cytochromes are and act to

 The electron transport system is made up of mitochondrial proteins, including enzymes and iron containing cytochromes.
The functional groups of cytochromes are iron atoms trapped by rings containing nitrogen and act to readily bind and release electron.

The functional groups of cytochromes are Iron atoms trapped by rings containing nitrogen and act to readily bind and release electrons.

Explanation:

The cytochromes were the primary elements to be detected, as a result of their distinctive, redox-sensitive, visible spectra. An individual cytochrome exhibits one major optical phenomenon in its change type, whereas most cytochromes show 3 absorption bands once reduced.
Most eukaryotic cells have mitochondria, that manufacture adenosine triphosphate from merchandise of the acid cycle, carboxylic acid oxidization, and aminoalkanoic acid oxidization. At the mitochondrial inner membrane, leptons from NADH and FADH₂ experience the electron transport chain to oxygen, that is reduced to water.