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1 OUTLINE IS INCOMPLETE – BUT GOOD REVIEW TO FILL IN DNA: Structure I. The genetic material: historical perspective A. Introduction: Until 1944 it was not clear what chemical component of the cell was the genetic material. How the answer to the question, “what is the genetic material?” was determined is one of the most fascinating stories in all of biology. Prior to 1944 it was known that: 1. ____________ were hereditary “factors” as described by Mendel 2. Genes code for ___________: ________________________hypothesis. (Although the process was not known). 3. Genes were carried on _______________ 4. Chromosomes consisted of ___________________________ The question remaining… what was the genetic material? Proteins, lipids, carbohydrates, or DNA? B. Experiment examining the nature of the genetic material: transformation 1. In 1928 Fredrick Griffith, a British medical officer, began his work with the bacterium Diplococcus . This bacterium, now named Steptococcus pneumoniae , causes pneumonia in certain vertebrates (e.g. humans and mice). 2. There are 2 strains of Diplococcus a. Virulent = ____- encapsulated with carbohydrate rich capsule; SMOOTH colonies b. Avirulent = _____- lacks a capsule so it is ROUGH; readily phagocytosed 3. See ppt slide for experiment . Hint: to fully understand an experiment, you should draw it yourself. 4. Result : The ____ genotype bacteria were ________________ to the ____ genotype via some “________________________”. He defined it as the compound transferred from the smooth to the rough bacteria and to direct capsule synthesis. But, what was the transforming factor?? C. First experiment demonstrating that DNA is the genetic material: 1944--Avery , McCarty and Macleod. These 3 researchers worked for 10 years to elucidate the “transforming factor” 1. Avery, McCarty and Macleod’s experiment: see ppt figure (hint: draw it) 2. Result:
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2 3. Final question: is the conversion of a bacterium from rough to smooth (i.e. the absence or presence of a carbohydrate-containing capsule) strong enough evidence to show that DNA is the genetic material for all forms of life on earth? What about showing that DNA was responsible for directing an entire lifecycle, not just its pathogenesis (or lack thereof)? D. Another historical experiment demonstrating that DNA is the genetic material: 1952—Hershey and Chase. Hershey and Chase used the bacteriophage T2, a virus that infects and kills E. coli. What did Hershey and Chase know about T2 at the time? 1. T2 is ~ 2. Production of new phage 3. T2 lifecycle Attachment to bacterium injection of genetic material into bacterium new phage parts assembled from bacterium’s macromolecules bacterium lyses many new phages are released 4. Hershey-Chase used radioactive isotopes to follow the molecular components through the phage lifecycle a. 32
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This note was uploaded on 11/04/2011 for the course BIOL 202 taught by Professor Kieber-hogan during the Fall '08 term at UNC.

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