Chapter 7 - Chapter 7 DNA Structure and Replication...

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Chapter 7: DNA Structure and Replication I) Discovery of transformation—mouse experiment A) Use of two distinguishable strains—one deadly (w/smooth appearance--S) and nonvirulent type (rough appearance—R) B) Killed virulent cells and injected them, the mice survived outside of cells do not cause depth C) Mice injected with mixture of heat-killed virulent and live non-virulent cells died D) Live cells could be recovered from dead mice, smooth colonies but were virulent, mice died cells had transformed E) To determine the killing agents, destroy one chemical component at a time and see if transformation still occurred, found that DNA was the transforming agent and genes are composed of DNA II) Hershey-Chase experiment A) Infecting phage must inject into bacterium the specific info that dictates the reproduction of new viral particles B) Phosphorous is in DNA but not proteins, sulfur is in proteins but not DNA C) Incorporated radioactivity phosphorous into DNA and sulfur into proteins D) After infection, took ghosts (empty phage carcasses) off cells and measured radioactivity. Most radioactivity in bacterial cells was phosphorous—DNA had entered cells E) Showed DNA was infecting agent III) DNA structure A) Contains phosphate, deoxyribose, and four nitrogenous bases (adenine, guanine, cytosine, thymine) 1) Carbon atoms in bases and sugar groups are assigned number 2) Purine—adenine and guanine have a double ring structure 3) Pyrimidine—cytosine and thymine have a single ring structure B) Arranged into groups nucleotides C) Chargraff’s rules of base composition 1) T+C = A+G 2) T=A and C=G D) Double (right handed) helix shape 1) Two strands held together by hydrogen bonds b/t the bases 2) Backbone composed of alternating phosphate and sugar units 3) Two backbones are in antiparallel (opposite) orientation 4) Has major and minor groove a) Major groove—DNA-protein associations 5) Observed radius only occurs if pyrimidine is paired with a purine a)
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