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Unformatted text preview: 2.20.2007 One gene one enzyme hypothesis Beadle and Tatum are trying to define the function of a gene and connection between genotype and phenotype Believed a gene encodes an enzyme which catalyzes a step in a biochemical pathway so a change in the nucleotide sequence in the gene would cause the enzyme to be nonfunctional which will cause the change in biochemical pathway which will cause deficiency of product or toxicity of substrate They believed ONE gene ONE enzyme BUT what if the gene doesnt encode a protein but instead snRNA, tRNA, ribozymes, rRNA and these products arent translated so the gene doesnt encode for an enzyme at all o OR Lets say the gene does encode for mRNA though, there is still alternative splicing, its no longer one gene, one enzyme, one gene can encode more than one enzyme o OR if it does encode a polypeptide (an mRNA then polypeptide) but its not an enzyme its an antibody, receptor, structural protein o OR if the enzyme is made up of multiple subunits and these are encoded by different genes therefore it would be who knows how many genes encoding one enzyme Then there was the idea (that is wrong) that what a gene does is to encode a polypeptide, that is what a gene doesthis addresses the multiple subunit problem, we arent saying the whole protein must be encoded by one gene we just say each subunit is the product of one gene (one polypeptide), also it addresses the issue of one gene one enzyme, it allows the idea that one gene might not have catalytic properties BUT it doesnt address alternative splicing, one gene can encode for more than one polypeptide. o And Could one gene encode fewer than one polypeptide? Yeah one gene could encode rRNA, snRNA, etc that is not a polypeptide ad all So what do genes really do o One gene, one or more gene products o Gene product = polypeptide or RNA End translation Mutations Mutation: heritable change in the genetic material o Genetic material: DNA o Says genetic material but genetic material could be RNA or virus o A change in your RNA is not a change that can be passed on though so its not heritable o Some viruses do use RNA as their genetic material so a mutation is a change in the RNA and is heritable here Heritable change o If you go out in bright sunlight and the UV changes your DNA is that heritable? Is that a mutation? It is not heritable in terms of parent of child But parent cells can pass on that change to the daughter cells so it is heritable in this sense o Heritable is not specific to parent to offspring it just means what is copyable or replicable by DNA polymerase o DNA polymerase can incorporate C, T, A and G so we are talking about different nucleotides in a sequence, a change in the order of the nucleotides in DNA if your talking cells is a heritable change Point Mutation o Small mutation, affects a small area, but small is a relative and variable descriptive word o A point mutation affects one nucleotide or one base pair...
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This note was uploaded on 04/07/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.
- Spring '08