Additional Case Study: Amino Acids and Evolution

Transcription

1 Student Worksheet Additional Case Study: Amino Acids and Evolution Objectives To use biochemical data to determine evolutionary relationships. To test the hypothesis that living things that are morphologically similar share similar protein structure. Background Information The sequencing of some 20 different amino acids is responsible for proteins, the building blocks of cells. Biologists knew that proteins are responsible for the morphological features of living things and hypothesized that organisms that share a similar heritage would demonstrate similarities in amino acid sequencing. Organisms most similar would have the most similarities in amino acids. Materials red and blue pens or highlighters Procedure 1. A segment of the enzyme cytochrome c, a protein involved in cellular respiration in aerobic organisms, is provided in Table 1. The entire enzyme consists of 104 subunits; however, only 50 amino acids are provided to represent the protein. The names of the amino acids have been abbreviated. As you can see, the sequence of amino acids is slightly different in three organisms. 2. Refer to Table 1 and calculate the percentage of each amino acid, as shown in the example below. Record your results in a table similar to Table 2. The percentage of alanine in the silkworm moth is 5(no. of alanines) = 10% 398 Chapter 13 The Evolutionary History of Life Copyright 2003 Nelson

2 Table 1 Amino Acid Sequence Silkworm Cys Ala His Cys Ala AsA Leu Val Try Ser Hornworm Cys Ala His Cys Ala AsA Leu His Try Ser Fruitfly Cys GluA His Cys Ala AsA Leu GluA Try Ser Silkworm Met GluA His Leu Arg Phe Ala Ser His GluA Hornworm Met GluA His Leu Arg Phe Ala Ser His GluA Fruitfly Met GluA His Leu Arg Phe Ala Ser His GluA Silkworm Thr His Tyr Try Ala Pro Phe AsA Val Thr Hornworm Thr Cys Tyr Try Ala Pro Phe AsA Val Thr Fruitfly Thr Cys Tyr Try Ala Pro His AsA Val Thr Silkworm GluA Tyr Pro Met Gly Val Arg Met Lys Phe Hornworm GluA Tyr Pro Met Gly Val Arg Met Lys Phe Fruitfly GluA Tyr Pro Met Gly Ala Arg Met Lys Phe Silkworm Thr Met Gly His AsA His Ala His Try GluA Hornworm Thr Met Gly His AsA His Ala His Try GluA Fruitfly Thr Met Gly His AsA His Ala His Try GluA (a) Complete the table in your lab book. Table 2 Amino Acid Percentage Abbreviation Amino acid name Silkworm moth Hornworm moth Fruitfly Ala Alanine 10% Arg Argenine AsA Aspartic acid Cys Cysteine GluA Glutamic acid Gly Glycine His Histidine Leu Leucine Lys Lysine Met Methionine Phe Phenylalanine Pro Proline Ser Serine Thr Threonine Try Tryptophan Tyr Tyrosine Val Valine Copyright 2003 Nelson Chapter 13 The Evolutionary History of Life 399

3 3. Refer to Table 1 to determine the number of different amino acids found in the hornworm moth and the fruitfly. Using the silkworm moth as the original, circle the amino acids in the hornworm moth that are different with a red pen. Repeat the procedure for the fruitfly, but use a blue pen. 4. Calculate the percentage difference by using the following formula: Number of differences in amino acid sequence 50 amino acids for silkworm moth 100 (b) Total the differences between amino acids for hornworm moth and silkworm moth. Calculate the percentage difference. (c) Do the same calculations for the fruitfly. 5. Using the hornworm moth as the original, draw an X in red through the amino acids in the silkworm moth that are different. Repeat the procedure for the fruitfly, but draw the X in blue. (d) Total the differences between the hornworm moth and the fruitfly. Calculate the percentage difference. 400 Chapter 13 The Evolutionary History of Life Copyright 2003 Nelson

4 6. Figure 1 is a computer-generated graphic based on similarities of amino acid sequencing of cytochrome c. Because this enzyme is found in most aerobic organisms, amino acid sequencing can be used to establish a phylogenetic tree. horse donkey dog Figure 1 pig Evolutionary relationship is established by percentage difference in amino acid sequencing. 7. You can determine the difference in amino acid sequencing by following the chart. For example, to determine the difference between the pig and the horse, draw a line along the phylogenetic tree that links the pig and the horse. Now add the distances represented by the changes in amino acid sequencing. Pig to the horse is: = 4.3% change in amino acid sequencing for cytochrome c. (e) Refer to the chart and indicate the differences in amino acid sequencing between the horse and the donkey. (f) Indicate the amino acid difference between the dog and the donkey. (g) Indicate the amino acid difference between the pig and the dog. Application Questions 1. Refer to Table 2 and indicate whether the hornworm moth is more closely related to the silkworm moth or the fruitfly. Explain your answer. 2. Refer to Figure 1 above, and indicate whether the donkey is more closely related to the horse, the dog, or the pig. Explain your answer. Copyright 2003 Nelson Chapter 13 The Evolutionary History of Life 401

5 Use the following phylogenetic tree to answer questions 3 and 4. horse pig dog debaryances candida brewer's 7.5 yeast neurospora man/chimp 0.8 rabbit dogfish monkey penguin chicken, turkey,duck turtle 6.5 tuna bonito bullfrog carp lamprey fruitfly silkworm moth hornworm screwfly moth INSECTS mung sesame bean castor wheat sunflower 3. Refer to the diagram and explain why some biologists suggest that the turtle thinks it s a bird. 4. Why might biochemical evidence suggest that the rabbit is less evolved than the horse and the pig? 5. What mechanism is responsible for the sequencing of amino acids? 6. Give reasons that support or reject the hypothesis that morphological similarities are supported by biochemical similarities. 7. Do you expect the phylogenetic tree constructed by comparing amino acid sequencing of cytochrome c would be similar to one based on other proteins? Give your reasons. 402 Chapter 13 The Evolutionary History of Life Copyright 2003 Nelson