Bio Test 3


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TEST 3 CHAPTER 12 DNA STRUCTURE AND FUNCTION 12.1 The Hunt for Fame, Fortune, and DNA A. Early and Puzzling Clues 1. Johann Miescher discovered DNA in the late 1800’s. 2. In 1928, Fred Griffith was working with S (pathogenic) and R (nonpathogenic) strains of a pneumonia-causing bacteria. 3. He performed 4 experiments: a. Injected mice with R cells; mice lived b. Injected mice with S cells; mice died c. S cells were heat-killed (made nonpathogenic) then injected into mice; mice lived. d. Live R (non) cells plus heat-killed S (non) cells were injected into mice; mice died! 4. Some substance form the S (pathogenic) cells has transformed the R cells into killers . a. Both proteins and nucleic acids were candidates b. In 1944, Oswald Avery showed that the (“Griffith”) substance was DNA B. Confirmation of DNA Function 1. Viruses called bacteriophages invade bacterial calls to reproduce 2. Alfred Hershey and Martha Chase used viruses to prove which (protein or nucleic acid) was the hereditary material. a. 35 S-labeled proteins in the viral coat did NOT enter the bacteria this were not used b. 32 P-labeled DNA in the vial core did enter the bacteria and direct new virus assembly . C. Enter Watson and Crick 1. Watson and Crick used numerous data to build various models of DNA 2. In 1953, they published the structure of DNA 2.2 The Discovery of DNA’s Structure A. DNA’s Building Blocks 1. Each of the four nucleotides consists of: a. 5-carbon sugar; deoxyribose ; b. A phosphate group; c. One of 4 bases- adenine (A), guanine (G), thymine (T), cytosine (C) 2. Edwin Chargaff , in 1949, showed the amount of A=T and the amount of G=C. 3. Rosalind Franklin made X-ray images of DNA a. DNA is a long, thin molecule of uniform diameter
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b. The structure of highly repetitive c. DNA is helical (coiled ) B. Patterns of Base Pairing 1. The models had these features: a. Single ringed I was hydrogen bonded with double ringed A , and single ringed C with double ringed G , along the entire length of the molecule b. The backbone was made of chains of sugar-phosphate linkage c. The molecule was double stranded and looked like a ladder with a twist to form a double helix 2. The base pairing is constant for all species but the sequence of base pairs in a nucleotide strand is different from one species to the next . 12.3 Rosalind’s Story (read pg 190) A. Rosalind Franklin was a superb practioner of x-ray crystallography 1. She worked on taking pictures of DNA and theorizing about its structure but was nut aggressive about publishing her results. 2. At one of her talks, she presented a DNA structure that was a helix but had too many chains and the phosphate groups projected outward . B. Her coworker, Maurice Wilkins, passed some of her images to Watson and
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This note was uploaded on 04/08/2008 for the course BISC 101 taught by Professor Sellers during the Fall '07 term at LA Tech.

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