Lecture 10 -Biochem-genetics

Lecture 10 -Biochem-genetics - Lecture 10 Biochemical...

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Unformatted text preview: Lecture 10 Biochemical genetics Before 1940, Geneticists studied visible traits, such as size, shape and color, in animals and plants. For most traits, there was no obvious connection between genes and the underlying biochemistry. flower pigment and fruit fly eye color were associated with changes in anthocyanin biosynthesis and tryptophan catabolism, respectively. Such examples (1) were represented by too few genes to reveal a metabolic pathway and (2) were involved in nonessential or secondary metabolism. One Gene, One Enzyme Hypothesis George Beadle and Edward Tatum contrived an experimental procedure to demonstrate: Genes were responsible for enzyme function. Each gene controlled a single enzymatic reaction. Traits were the result of biochemical reactions. The idea was simple Select an organism like a fungus that has simple nutritional requirements... Induce mutations by radiation or other mutagenic agents Allow meiosis to take place so as to produce spores that are genetically homogeneous. Grow these [mutants] on a medium supplemented with an array of vitamins and amino acids. Test them by vegetative transfer to a medium with no supplement. Those that have lost the ability to grow on the minimal medium will have lost the ability to synthesize one or more of the substances present in the supplemented medium. From George W. Beadles (1958) Nobel Lecture Biochemical genetics of Neurospora Select an organism like a fungus that has simple nutritional requirements... The genome of a bacterium or fungus encodes enzymes for biosynthesis of most if not all of amino acids and nucleotides that the microbe requires. A prototrophic organism or strain can grow in minimal medium, which contains a single carbon & energy source and inorganic salts for other constituent elements. An auxotrophic strain lacks biosynthetic capacity for specific organic constituent(s) such as an amino acid, pyrimidine or purine, which must be supplemented for growth in minimal medium. Spontaneous mutation is very rare....
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This note was uploaded on 07/08/2009 for the course LIFESCI ls 4 taught by Professor Merriam during the Winter '08 term at UCLA.

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Lecture 10 -Biochem-genetics - Lecture 10 Biochemical...

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