Lecture5 Notes

Lecture5 Notes - Wed 8.12.09 Lecture 5 DNA Structure I The...

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Wed. 8.12.09 Lecture 5: DNA Structure I. The Discovery of DNA as the Genetic Material Discovery of DNA o 1860s: Gregor Mendel (“father of genetics”) presents studies on heredity in peas Peas used since the genetic traits can be easily sighted. Zygote: combination of genetic information from both parents. o 1869: Friedrich Miescher isolated large substance in nucleus of white blood cells in pus from surgical bandages. Slightly acidic, sugary, rich and phosphorus Called it “nuclein” o 1920s: Genetic materials are in chromosomes, which are in the nucleus Chromosomes contain a variety of proteins in addition to DNA. Prevailing view among biologists during this time was that proteins were the chief carriers of heredity. o Nucleic acids have 4 different building blocks while proteins have 20 different building blocks. Therefore, believed that DNA is not enough to store information for all the living organisms. o 1929: P.A. Levene determined the chemical composition and structure of the building blocks of DNA. o But the scientific world strongly believed that DNA is not as complex as protein to be the genetic material. o It wasn’t until a series of experiments performed by Fredrick Griffith (19298), Avery, MacCleod, McCarty, Chargaff, and Hershey and Chase (1952) that convinced the scientific community that DNA, and not proteins, is the heritable, genetic material. Frederick Griffith 1928 o An army doctor; wanted to make a vaccine against streptococcus pneumoniae (aka: pneumococcus causes a type of pneumonia) o Since the time of Pasteur, vaccines had been made using killed microorganisms which could be injected into patients to elicit the immune response of live cells without the risk of disease. o Though he failed in making the vaccine, he stumbled on a demonstration of the transmission of genetic instructions by a process we now call the “transformation principle” o Strain S: virulent; causes pneumonia Smooth appearance due to polysaccharide capsule; evade host’s immune system. o Strain R: non-virulent
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Rough appearance; lacks polysaccharide capsule; recognized by the host’s immune system. o Experiment 1: Fractionate bacteria cells (RNA, protein, DNA, lipid, and carbohydrates) and tested each type of molecules for its ability to transform R to S. Turned out that DNA is the ONLY molecule that can do the
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Lecture5 Notes - Wed 8.12.09 Lecture 5 DNA Structure I The...

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