Ro_Lecture9

Ro_Lecture9 - One gene One enzyme hypothesis In the next...

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1 One gene One enzyme hypothesis In the next few lectures, the following questions will be Addressed: What is the structure of a gene? How does a gene function? How is information stored on the gene? What is the relationship between genotype and phenotype? Duchene muscular dystrophy is a human disease caused by an X-linked recessive mutation. DMD affects one in 3500 males. Age of onset is between one and six years. Affected individuals are often initially identified because they rise from the prone position in an unusual manner.
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2 DMD
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3 Pathways Biologists and clinicians want to address the question of how altering a particular set of base pairs that make up the 3 billion base pairs in the human genome led to this phenotype. Formal genetics provides little information about these intermediary steps. Since the 1970’s, a set of techniques have been developed that enable us to elucidate each step in a pathway - These techniques are generally placed under the rubric of Molecular Biology or Molecular Genetics DNA RNA Protein Protein complex Cellular phenotype Organism phenotype
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4 DMD Through these techniques, it was found that DMD patients have a mutation in a single gene. The normal function of the gene is to enable muscle fibers to make a protein called dystrophin. Dystrophin localizes to the plasma membrane in muscle cells. The normal dystrophin protein stabilizes the muscles during muscle contractions. Muscle fibers in people affected with DMD are extremely deficient in dystrophin. Without this protein, the plasma membrane ruptures during muscle contraction and degeneration of the muscle tissue occurs.
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5 Huntington's Disease Huntington's disease (HD) results from degeneration of neurons, in certain areas of the brain. This degeneration causes uncontrolled movements, loss of intellectual faculties, emotional disturbance and early death This disease is caused by a single dominant mutation on the Forth chromosome. Each child of an HD parent has a 50-50 chance of inheriting the mutation. A person who inherits the mutation will sooner or later develop the disease! To understand this disease we need an interdisciplinary Approach. DNA Geneticist Bioinformatics RNA Molecular biologist Protein Biochemist Protein complex Biochemist Cellular phenotype Cell biologists Organism phenotype Physicians
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6 Beadle and Tatum The experiments of Beadle and Tatum in the 1940’s provided the first insight into gene function. They developed the one gene/one enzyme hypothesis This hypothesis has three tenets: 1 Molecules are synthesized as a series of steps 2 Each step is catalyzed by an unique enzyme 3 Each enzyme is specified by a unique gene The logic: Precursor Int1 Int2 Product EnzA EnzB EnzC GeneA GeneB GeneC
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7 Consequences of mutations Precursor Int1 Int2 Product EnzA EnzB EnzC GeneA GeneB GeneC Lets say we know the biochemical pathway. With this pathway, what are the consequences of a
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Ro_Lecture9 - One gene One enzyme hypothesis In the next...

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