Cytochrome evolutionary tree

Draw an evolutionary tree for the human, rabbit, silkworm, and Neurospora (fungus) by using the data in the following table for differences in the respective cytochrome c sequence. 

These data allow us to construct an evolutionary tree, with branch lengths approximately proportional to the number of differences between the species (see Fig. 4-10). The human and rabbit show most similarity and therefore are connected by short branches. The silkworm cytochrome c is closer to both mammalian forms than it is to Neurospora, and so should be connected to the mammalian junction. The length of the silkworm branch will be approximately three times the length of the rabbit and human branches. Finally, Neurospora shows approximately the same number of differences with all the animal species, and therefore can be joined to their common branch. 

Figure 18.24. Evolutionary Tree Constructed From Sequences of Cytochrome C. Branch lengths are proportional to the number of amino acid changes that are believed to have occurred. This drawing is an adaptation of the work of Walter M. Fitch and Emanuel Margoliash.

The resemblance among cytochrome c molecules extends to the level of amino acid sequence. Because of the molecule s relatively small size and ubiquity, the amino acid sequences of cytochrome c from more than 80 widely ranging eukaryotic species were determined by direct protein sequencing by Emil Smith, Emanuel Margoliash, and others. Comparison of these sequences revealed that 26 of 104 residues have been invariant for more than one and a half billion years of evolution. A phylogenetic tree, constructed from the amino acid sequences of cytochrome c, reveals the evolutionary relationships between many animal species (Figure 18.24). 

Evolutionary Relationships of RC The types of RC complexes, in terms of the presence or absence of the cytochrome subunit, are summarized in Fig. 4-f together with the type of soluble cytochrome C2 and quinone species in the membrane. The phylogenetic tree was based on 16S ribosomal RNA sequence (4) and the information described above (7,8). 

Fig. 2.47. The rate of evolutionary changes in amino add sequence of three different proteins, cytochrome c, hemoglobin, and fibrinopeptides. In absdssea, the time needed for a 1% change in sequence between two diverging branches of the phylogenic tree (in million years), in ordinates the number of corrected amino add changes for 1(X) residues. The slope allows one to obtain the rate of mutation (in million of years) (according to Dickerson, 1971).

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