Based on the cytochrome c data, which organism is most closely related to humans?

Cytochrome c is a protein that plays a vital role in cellular respiration, the process of converting oxygen and nutrients into energy. Cytochrome c transfers electrons between two complexes of enzymes in the mitochondrial membrane, known as Complex III and Complex IV. Cytochrome c is also involved in apoptosis, or programmed cell death, by triggering a cascade of reactions that lead to cell death when released from the mitochondria.

Cytochrome c is a highly conserved protein, meaning that its amino acid sequence is very similar across different species. This suggests that cytochrome c has a very important function that has been maintained throughout evolution. By comparing the amino acid sequences of cytochrome c from different organisms, we can infer how closely related they are to each other and to humans.

How to compare cytochrome c sequences

One way to compare cytochrome c sequences is to count the number of differences or substitutions between them. For example, human cytochrome c has 104 amino acids, and horse cytochrome c has 11 amino acids that are different from human cytochrome c. Therefore, the number of substitutions between human and horse cytochrome c is 11. The fewer the substitutions, the more closely related the organisms are.

Another way to compare cytochrome c sequences is to construct a phylogenetic tree, which is a diagram that shows the evolutionary relationships among organisms based on their similarities and differences. A phylogenetic tree can be constructed using various methods, such as maximum parsimony, maximum likelihood, or Bayesian inference. These methods use mathematical models and algorithms to find the most probable or optimal tree that explains the observed data.

According to Wikipedia, the following table shows the number of substitutions between human cytochrome c and cytochrome c from various organisms:

OrganismSubstitutions
Chimpanzee0
Rhesus monkey1
Dog13
Horse11
Kangaroo12
Chicken18
Penguin17
Tuna21
Yeast44

Based on this table, we can see that chimpanzee cytochrome c is identical to human cytochrome c, which means that chimpanzees are the most closely related organism to humans based on cytochrome c data. Rhesus monkeys are also very closely related, with only one substitution. Dogs, horses, and kangaroos are more distantly related, with about 10-13 substitutions. Chickens and penguins are even more distant, with about 17-18 substitutions. Tuna is very different from humans, with 21 substitutions. Yeast is the most divergent organism from humans, with 44 substitutions.

A phylogenetic tree based on cytochrome c data can be seen in PDB-1012, which shows the evolutionary relationships among various organisms based on their cytochrome c sequences. The tree confirms that chimpanzees are the closest relatives of humans, followed by rhesus monkeys and other primates. The tree also shows that mammals form a distinct group from birds and fish, and that yeast is an outgroup that diverged very early from other eukaryotes.

Conclusion

Cytochrome c is a useful protein for studying molecular evolution because it is highly conserved and widely distributed among living organisms. By comparing the amino acid sequences of cytochrome c from different organisms, we can estimate how closely related they are to each other and to humans. Based on cytochrome c data, chimpanzees are the most closely related organism to humans, followed by rhesus monkeys and other primates.

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