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BIO207H5 (42)
Chapter 4

Chapter 4 - Textbook Notes.docx

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University of Toronto Mississauga
Nicole Myers

Chapter 4Gene Functiontextbook notesGene Control of Enzyme Structure Garrods Hypothesis of Inborn Errors of Metabolism1902Archibald Garrod physician and William Bateson geneticist studied alkaptonuriaOMIM203500 a human disease characterized by urine turning black upon exposure to air and the tendency to develop arthritis later on in life Many human diseases are recessivemeaning that to develop the disease an individual must inherit one recessive mutant allele for the gene responsible for the disease from each parentmaking that individual homozygous recessive for the alleleGarrod found that people with alkaptonuria excrete homogentisic acid HA in their urine whereas people without the disease do not it is HA in the urine which turns it black This result indicated that normal people can metabolize HA and those with the disease cannot The disease is an example of inborn error of metabolismthat is alkaptonuria is a genetic disease caused by the absence of a particular enzyme necessary for HA metabolism The mutation responsible for alkaptonuria is recessive so only people homozygous for the mutant gene express the defectLocation of gene on chromosome 3The OneGeneOneEnzyme Hypothesis1942George Beadle and Edward Tatumbegan the study of biochemical geneticOnegeneoneenzyme hypothesisdirect relationship between genes and enzymesgenes act by regulating definite chemical eventsPrototrophic strain phototrophcan grow on the minimal mediumsynthesizes other materials needed for growth from the simple chemicals present in the minimal medium Nutritional mutants auxotrophic mutants or auxotrophsminimal medium in which nutritional supplements such as amino acids or vitamins are added To isolate auxotrophic mutants an xray is a mutagen mutation generator an agent that induces mutantscrosses other strains of different mating typesensuring isolated strains were heritable and therefore had a genetic basis rather than a nongenetic reason for requiring the nutrient By identifying the strain that is an auxotroph by placing it minimal mediums plus one amino acid one will be able to identify which amino acid is required for the strain to grow
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