The Evolutionary Significance of Cytochrome c


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By Vossman – Own work, CC BY-SA 3.0,

OpenStax Biology 2e

Cytochrome c is an important component of the electron transport chain, a part of cellular respiration, and it is normally located in the cellular organelle, the mitochondrion. This protein has a heme prosthetic group, and the heme’s central ion alternately reduces and oxidizes during electron transfer. Because this essential protein’s role in producing cellular energy is crucial, it has changed very little over millions of years. Protein sequencing has shown that there is a considerable amount of cytochrome c amino acid sequence homology among different species. In other words, we can assess evolutionary kinship by measuring the similarities or differences among various species’ DNA or protein sequences.

– What is a series of complexes that transfer electrons from electron donors to electron acceptors via redox reactions?

Scientists have determined that human cytochrome c contains 104 amino acids. For each cytochrome c molecule from different organisms that scientists have sequenced to date, 37 of these amino acids appear in the same position in all cytochrome c samples. This indicates that there may have been a common ancestor. On comparing the human and chimpanzee protein sequences, scientists did not find a sequence difference. When researchers compared human and rhesus monkey sequences, the single difference was in one amino acid. In another comparison, human to yeast sequencing shows a difference in the 44th position.

– What is an important component of the inner mitochondrial membrane where the cytochrome c binds to and constitutes about 20% of the total lipid composition?

One of the ways cell apoptosis is activated is by release of cytochrome c from the mitochondria into cytosol. A study has shown that cells are able to protect themselves from apoptosis by blocking the release of cytochrome c using Bcl-xL. Another way that cells can control apoptosis is by phosphorylation of Tyr48 which would turn cytochrome c into an anti-apoptotic switch.


Clark, M., Douglas, M., Choi, J. Biology 2e. Houston, Texas: OpenStax. Access for free at:


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