Lecture 30 DNA

Lecture 30 DNA - DNA: The Genetic Material Lecture 29...

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DNA: The Genetic Material Lecture 29 Campbell - Chapter 16 pp 293-298 and information in these notes Learning objectives Explain the experiment by Griffith that provided evidence for genetic transformation. Explain the experiment of Avery, MacLeod, and McCarty that supported the hypothesis that DNA is the hereditary material. For each hypothesis tested, explain what result the hypothesis predicted in each experiment performed. Explain the experiment of Hershey and Chase that supported the hypothesis that DNA is the hereditary material. Explain how the structure of DNA explains Chargaff’s rules. Explain how Watson and Crick’s model of DNA structure explains the copying mechanism for the genetic material. Understand the goals of functional and comparative genomics.
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The burning question from 1900-~1940: What is the molecular nature of the gene? It was known that chromosomes contained genes. But chromosomes are comprised of two components: protein and DNA. Why were proteins considered the best candidates for the genetic material? Proteins are macromolecules that vary in structure and composition, while DNA is a simple, uniform molecule. Therefore protein has the complexity required to specify a great deal of information. Protein DNA
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The following experiments provided evidence that DNA is the genetic material: 1. Transformation of bacteria ( Griffith; Avery, McCarty, and MacLeod) 2. Radioactive labeling of protein or nucleic acid in T2 phage ( Hershey and Chase ) 3. Comparative analysis of the variability of DNA composition from organism to organism, coupled to the regularity in the ratios of bases ( Chargaff) 4. Structural analysis of DNA ( Watson, Crick, Franklin )
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Bacterial transformation Griffith’s initial discovery in 1928 (shown above) was that the living R cells had been transformed into pathogenic S cells by some, unknown heritable substance from the dead S cells. “Smooth” cells have polysaccharide coat and are pathogenic. “Rough” cells lack this coat and are non pathogenic. Griffith injected mice with these two bacterial strains as shown below. R cells had acquired from the dead S cells the ability to make poly- saccharide coat
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In 1944, 16 years later, after a decade of research Avery, McCarty, and MacLeod discovered that this chemical component was DNA. They did this by using Griffith’s system and asking what component from the heat-killed S pathogenic bacteria was able to transform the live nonpathogenic R strain.
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The experiment: Dead heat killed S cells were divided in 3 tubes.  Enzymes that degrade DNA, RNA, or proteins, were 
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This note was uploaded on 03/31/2009 for the course BIO 202 taught by Professor Dean during the Spring '08 term at SUNY Stony Brook.

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Lecture 30 DNA - DNA: The Genetic Material Lecture 29...

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