Molecular comparisons between species

Molecular evidence from comparisons of amino acid sequences of proteins and of the nucleotide sequences of mitochondrial DNA can be used to reveal similarities between related species

Comparing amino acid sequences of protein

For many proteins small changes in amino acid sequence leave the overall structure and the funciton of the protein unaltered. Typically, the part of the molecule essential for its function (such as the active site of an enzyme) remains the same, but other parts of the molecule may show changes

When the amino acid sequence of a particular protein is compared in different species, the number of differences gives a measure of how closely related the species are

Our exmple will be cytochrome c, a componenet of the ETC in oxidative phosphorylation in mitochondria. A protein with such an important function is expected to have a similar sequence of amino acids in different species since a poorly adapted cytochrome c molecule would result in the death of the organism. When the sequences of cytochrome c from humans, mice and rats were compared, it was found that:

• all three molecules consist of 104 amino acids
• …