Understanding Hemophilia - Potential Treatments through the Central Dogma of Molecular Biology

Central Dogma Card Sorting Activity Student Handout INTRODUCTION Hemophilia is a rare genetic disorder in which the blood does not clot properly because it lacks sufficient bloodclotting proteins. The disease is caused by mutations in a gene on the X chromosome. Because males typically have only one X chromosome, to inherit the disease, they only need to inherit one copy of the mutated gene, whereas females with two copies of the X chromosome must inherit two copies of the mutated gene. Symptoms of the disease vary but generally include excessive internal and external bleeding. Currently, there is no longterm cure, and many patients receive infusions of blood-clotting proteins. Because the disease is caused by mutations in the DNA, scientists think that they could someday treat it by intervening in the steps that occur from DNA to protein production. This flow of information represents the way most genes are expressed in eukaryotic cells and is also referred to as the central dogma of molecular biology. How would knowledge of the central dogma help find a treatment for hemophilia? Working in small groups or alone, you will place cards with drawings of cellular molecules in the order in which the steps occur in eukaryotic gene expression, labeling all names and molecules as instructed. Then, answer the questions that your instructor assigns. QUESTIONS 1. A genotype is the complete genetic makeup of an individual, whereas a phenotype is all observable characteristics of the individual. Because genes direct the production of proteins and proteins are responsible for an individual’s observable characteristics, genotypes control phenotypes. The final card in the series shows a mature protein. Proteins can play several different cellular functions, as shown in the figure below. Using prior knowledge, describe a specific role each type of protein performs for the cell and provide an example of an actual protein (e.g., lactase). Write your answer next to each picture. Struture: proteins that perform role in a cell or tissure by giving the cell its shape or support. Examples: microfilaments, keratin, actin, collagen, and dystrophin Transport: proteins that move materials into, out of, or throughout cell,tissue, or examples: hemogoblin, sodium-glucose co-transporter ATP synthase, and the sodiumpotassium pump. Enzymes: catalytic proteins that Channels: proteins that allow the speed up chemical reactions by transport of specific substances lowering the activation energy across a cell membrane. Examples: required for the reaction. Examples: sodium channels, calcium channels, pepsin, amylase, lactase, DNA and aquaporins. polymerase, and RNA polymerase Central Dogma Card Sorting Activity Questions 2-4 present different disease scenarios. For each one you are asked to identify a way to treat the disease by targeting a specific molecule or step in the central dogma pathway. Refer to your cards as you think of an answer and make sure you pick a different approach for each disease. 2. Cystic fibrosis is a devastating illness that affects the lungs, pancreas, and intestines. In 1989, researchers discovered that the disease is caused by a mutation in a gene that produces a protein that channels chloride across cellular membranes. People with two copies (or alleles) of the mutated gene have a buildup of mucus in the lungs, intestines, and other organs due to nonfunctioning or absent channel proteins. Suggest two ways you could intervene to treat the disease by targeting the DNA molecule and justify why each approach could be effective. You can fix the gene by changing the DNA sequence, Use CRISPR-Cas9 technology to edit the DNA structure. Or introduce a non mutated gene into the appropriate cells. 3. Like cystic fibrosis, sickle cell anemia is an autosomal recessive condition. It can be caused by mutations in the gene for β-globin (HBB). HBB is one of the two subunits of adult hemoglobin, the protein that carries oxygen in red blood cells. People who inherit two copies of the mutation produce abnormal hemoglobin, and their tissues are starved of oxygen. One interesting finding is that some individuals with HBB mutations do not have sickle cell anemia because they have another mutation that allows them to produce fetal hemoglobin throughout their lives. Fetal hemoglobin production is normally turned off after birth. Based on this knowledge, suggest two ways you could treat sickle cell anemia by targeting the transcription step of the fetal hemoglobin gene and justify why each approach might be effective. introducing the necessary activators and transcription factors to begin transcription or a way to remove any repressors that might be present keeping the transcription of the fetal hemoglobin gene off 4. Another disease caused by a mutation in a single gene is Huntington’s disease (HD), an autosomal dominant condition. It is caused by mutations in a gene required for normal nerve cell function. The mutations cause abnormal proteins to be produced which “stick” together and accumulate in nerve cells, eventually interfering with normal cell operations. Suggest two ways you could treat the disease by targeting the translation step for the HD protein and justify why each approach might be effective. blocking the mRNA from being translated by the ribosome or destroying the mRNA so that it cannot be translated. 5. (Optional) For any genetic disease, several approaches for treating it at different steps of gene expression could work. Complete the Click & Learn “Central Dogma and Genetic Medicine,” paying particular attention to the genetic medicines that have been developed or are in development for the diseases above. Were the approaches you identified in this activity like the ones in the interactive? If so, how were they similar? If not, how did they differ? 6. Consider hemophilia again. Identify two ways the researcher could design an intervention to treat hemophilia, provide a brief explanation of each, and justify why each approach might be effective. gene therapy introducing a healthy gene into the proper blood cells that secrete the specific clotting factors; CRISPR-Cas9 to edit the gene in the proper blood cells that secrete the specific clotting factors; or develop a small-molecule oral drug that increases the concentration of clotting factors similar to the current infusions.