Assignments for non-majors
These assignments will enable you to study the effects of mutations in the globin gene for 17 patients and learn how these mutations affect the health of each patient. For your ease in completing each assignment, the background text relevant to the experiment that you will perform is in red, instructions for each assignment are indicated by plain text, and questions or activities that you will be asked to provide answers for are indicated by bold text.
The following assignment is designed to help you become familiar with the operation of HemoglobinLab by studying sickle-cell disease.
Getting to Know HemoglobinLab: Sickle-Cell Disease
Chills, fever, headache, and vomiting are but a few symptoms of the disease called malaria. Malaria is caused by a protozoan, Plasmodium vivax, that lives in tropical countries and reproduces in a mosquito called the Anopheles mosquito. Plasmodium is transmitted to humans when an infected mosquito bites a human and sporozoites, an infectious stage of Plasmodium, enter the human bloodstream and travel to the liver. Sporozoites reproduce in liver cells and release progeny called merozoites into the bloodstream which infect red blood cells, reproduce, and rupture these cells to infect more red blood cells. Individuals who are heterozygous for sickle-cell disease have a higher resistance to malaria than wild type individuals. This resistance occurs because the fragile structure of sickled red blood cells interrupts the life cycle of Plasmodium.
1. Select the Blood Samples view on the input screen for HemoglobinLab. Scroll down the Select Case list and choose patient Miriam Dembele. Read Miriam's case history. Note that her case history is consistent with increased resistance to malaria. Compare Miriam's blood sample with the healthy control sample. Are there any obvious differences? Select the Microscope view and make note of any obvious differences in red blood cell structure. Do any of the red blood cells show phenotypic characteristics of sickle-cell disease? If so, approximately what percentage of her cells show these characteristics?
2. Select the Gel Electrophoresis view to examine the electrophoretic migration pattern for the beta globin subunits of Miriam's hemoglobin as compared with a control sample from a healthy patient. Is the migration pattern of Miriam's hemoglobin indicative of a mutation in one of her globin genes? Is Miriam homozygous or heterozygous for this mutation? Explain your answer.
3. Select the Peptide Sequence view. Click the Find Difference button to identify the amino acid change in Miriam's hemoglobin compared with the normal control hemoglobin. Differences in the amino acid sequence of Miriam's hemoglobin protein compared with the normal protein will align at the far left of the screen. Which amino acid has been substituted for in Miriam's gene? Note the position of this amino acid change. This will be important for identifying the position of the nucleotide change in the globin gene.
4. Select the Edit DNA Sequence view. Miriam's globin gene sequence appears, compared with the normal, wild-type globin gene sequence. First, you will need to locate the DNA sequence with the triplet ATG that indicates the position of the start codon that would appear on globin mRNA produced by transcription of this gene. You can do this either by scanning the gene by clicking on the double arrows or (more easily) by typing ATG in the Search window and hitting the return key. This will take you to the ATG with the A in nucleotide 87 outlined with a red box. Click on the Bracket Codons button to outline codons beginning at the ATG. Use the single arrow to advance to codon 6 (nucleotides 105 - 107).
Click on nucleotide 106--it should now be outlined with a red--and change the A to a T. Click the Translate button to see a comparison of your custom-mutated protein to Miriam's protein sequence and the normal protein.
Is this mutation consistent with what you know about the most common mutation that causes sickle-cell disease?
Refer to a codon chart by clicking on the Genetic Code button at the top of the HemoglobinLab homepage and identify the normal codon and the mutated codon that you changed to simulate the amino acid change in Miriam's hemoglobin.