Part 3: Modeling Abnormal Hemoglobin (8 points)
In this part, you will model how a change in a single nitrogenous base in DNA changes the structure of hemoglobin and causes sickle cell anemia.
14. The sequence of bases for the same segment of DNA is shown below. However, a mutation has caused a single thymine molecule to be replaced by an adenine. The mutation is shown in boldface. Determine how this change affects the corresponding mRNA codon and amino acid sequence. Record the full mRNA and amino acid sequences in the table below. (2 points)
15. Use more labeled paper circles to make a model of the polypeptide segment that would result from the mutated gene segment. Draw or attach a photo of both the finished sickle-cell polypeptide and the normal polypeptide. (2 points)
16. The hemoglobin proteins that form from the sickle-cell polypeptide stick together to form stiff rods within red blood cells. Normal hemoglobin molecules do not stick together. Using clay balls to represent hemoglobin and string to represent cell membranes, make a model to compare the hemoglobin molecules in a sickle-shaped cell and in a normal red blood cell. Draw or attach a photo of your model in the space below. (4 points)
Analysis and Conclusions (22 points)
1. In Step 3, you verified the base sequence in the DNA template strand. Why was this verification important to the final polypeptide model that you made in Part 2? Did you find errors that you needed to fix? What could have happened to the final polypeptide if there had been uncorrected errors in the template strand? Use evidence from your models to support your answers. (4 points)
2. Explain what your model in Step 10 does and does not show about the process of transcription. (4 points)
3. Compare your model of the results of translation from Step 10 with your model of the results of transcription from Step 13. How does the change in the location of the mRNA molecule demonstrate the purpose of transcription? (2 points)
4. Explain how you modeled translation in Part 2. (2 points)
5. How could you revise your model in Part 2 to show how tRNA is involved in translation? (2 points)
6. How do the two beta globin polypeptide models you made in Step 15 differ? Use your models to explain the cause and effect of this difference in terms of the DNA, RNA, and hemoglobin structures. (4 points)
7. Use the models you made in Part 3 to explain how the resulting changes in the structure of hemoglobin affect its function in the body. (2 points)
8. Sugars consist of atoms of carbon, hydrogen, and oxygen. Sugars and other molecules can be broken down and their parts used to make other biomolecules your body needs. Explain why sugars are important to the formation of proteins such as hemoglobin. (1 point)
9. Humans cannot make certain amino acids, including valine (Val), leucine (Leu), and lysine (Lys). They get these amino acids from the food they eat. Review the amino acids in your model polypeptides. Then revise your answer to question 8 to include this new information. (1 point)
