Solomon IM Ch 12

Solomon IM Ch 12 -...

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Instructor’s Manual for Solomon, Berg, and Martin’s Biology, 9 th Edition 114 12 DNA: The Carrier of Genetic Information Lecture Outline I. Evidence that DNA is the hereditary material was first found in microorganisms. A. Early biologists believed that the genetic material was a protein. B. Frederick Griffith in 1928 studied pneumococcus bacteria in mice. 1. Smooth (S) strain was virulent. 2. Rough (R) strain was not virulent. 3. Heat killed S strain was not virulent (= avirulent). 4. A combination of heat killed S strain and R strain was virulent. a) Posed the question: “Why?” 5. Something caused the R strain to become virulent (called it transformation). C. This “transforming principle” was later identified by Avery and colleagues in 1944 as DNA, while ruling out that it was from the lipid, protein, or polysaccharide fraction from the cells. D. In 1952, Alfred Hershey and Martha Chase’s experiments on bacteriophages ruled out that it was from the lipid, protein, or carbohydrate fraction from the cells. 1. Bacteriophages are viruses that infect bacteria, and they are known to leave their protein coat (capsid) on the outside of the bacterium that they infect. 2. Labeled the protein coat with radioactive sulfur, the DNA with radioactive phosphorus in two separate cultures. 3. Found that only the phosphorus was in the bacterium after infection with the bacteriophages, thus providing further evidence that DNA is the genetic material (at least in those viruses in this study). 4. Edwin Chargaff determined that the ratio of adenine to thymine and the ratio of guanine to cytosine were always the same in all organisms tested. II. Elucidated by Crick and Watson in 1953, the structure of DNA allows it to carry information and to be faithfully duplicated. A. Nucleotides can be covalently linked in any order to form long polymers. 1. DNA is a nucleotide based molecule containing deoxyribose, phosphate, and one of the four nitrogen containing bases. 2. The bases of DNA are purines (adenine and guanine) and pyrimidines (thymine and cytosine). 3. Nucleotides are covalently bonded with a sugar phosphate backbone. a) The linkage forms a 3 ʹ , 5 ʹ phosphodiester linkage. b) No matter the length, one end of the molecule has a free 5 ʹ carbon attached to a phosphate; the other end has a free 3 ʹ carbon attached to the hydroxyl group.
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Chapter 12: DNA: The Carrier of Genetic Information 115 B. DNA is made of two polynucleotide chains intertwined to form a double helix. 1. Rosalind Franklin and Maurice Wilkins did x ray diffraction analyses on DNA; this data was available to Crick and Watson. a) Results showed that the molecule was helical and had several repetitive elements at 0.34 nm, 3.4 nm, and 2.0 nm apart. b)
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This note was uploaded on 11/17/2011 for the course BIO 101 taught by Professor Martin during the Spring '08 term at Rutgers.

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Solomon IM Ch 12 -...

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