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How do proteins differ among species?
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Protein
The molecular structure of a peptide (a small protein) consists of a sequence of amino acids.
Proteins differ among species because they are informational macromolecules that reflect the hereditary information stored in DNA. As species evolve, their amino acid sequences change over time, typically one unit at a time. By comparing the number of differing units in homologous proteins between organisms, scientists can quantify evolutionary relationships and estimate the recency of a common ancestor.1
The degree of difference depends on the protein's rate of evolution:
- Slowly evolving proteins: Proteins like cytochrome c are highly conserved, meaning they share a large proportion of amino acids even across distantly related species. Because they change so slowly, they are useful for studying remote evolutionary events but may be identical in closely related species.12
- Rapidly evolving proteins: Proteins such as fibrinopeptides evolve quickly, making them better suited for reconstructing the history of recently diverged species.2
- Intermediate rates: Proteins like hemoglobin evolve at moderate rates, providing utility over a broader range of evolutionary time.2
Because the genetic code is redundant, some DNA changes do not result in amino acid substitutions, meaning protein differences provide a specific, quantifiable reflection of evolutionary history.12