Comparing amino acid sequences in proteins has been used to determine the relatedness of organisms. Below is a graphic that shows the amino acid sequence differences between different organisms for a protein keratin. Changes in amino acid sequences are known to cause changes in structure of proteins. Species A Species B Species C Species D Species E Species A 4 11 19 1 Species B 12 18 5 Species C 8 10 Species D 20 Species E Part A. Consider species A, D, and E. Using the data provided, describe how the structures of their keratin proteins would compare. Part B. Keratin is made up of about 450 amino acids. Determine the similarity in percentages between species A and B, A and C, and B and C. Explain how amino acid sequences can be used in determining how closely related two species are. Part C. Based on this data, predict which two species would be more closely related to one another. Part D. Justify your predictions to part C.

A) Species A and E are more closely related than either species are related to species D.

B) Between A and B = 99.1%

Between species A and C =97.5%

Between species B and C = 97.3%

Similarity in amino acids sequence reflects similarity in DNA sequence

C) Species A and E are most closely related

D) Species A and E have the most similarity in amino acid sequence, and hence DNA sequence.

Explanation:

A) The amino acid sequences of the protein, keratin, in species A and D has a difference of about 19 whereas species A and E have a difference of only 1. Therefore, it means that keratin in species A and D will have differences in structure whereas between species A and E, they would have almost the same structure.

Also, species D and E have a difference of 20 in their amino acids sequence, therefore, the structure of keratin in both species will have differences in structure.

B) Similarity between A and B:

450 - 4 = 446

In percentage: 446/450 × 100% = 99.1%

Similarity between A and C:

450 - 11 = 439

In percentage: 439/450 × 100% = 97.5%

Similarity between B and C:

450 -12 = 438

In percentage: 438/450 × 100% = 97.3%

The sequence of DNA of species determines their amino acid sequences because information in DNA is transcribed to RNA which are then used to make proteins. Therefore, if a species are very closely related, they are expected to have very similar genetic sequences and thus proteins too. This is reflected in similarity between amino acid sequences in their proteins.

C). Species A and E are most closely related.

D) Species A and E have only a single difference in their amino acids sequence for Keratin. This translates to about 99.7% similarity which is the highest among all the species compared. Therefore, species A and E are most closely related.