CH 5 DNA and Chromosomes

CH 5 DNA and Chromosomes - 10/19/09 Chapter 5 DNA and...

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10/19/09 1 Chapter 5 DNA and Chromosomes 05_02_DNA.jpg Chemical basis of genes
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10/19/09 2 Historical perspective on the chemical nature of genes • The chemical nature of genes was established over a period of about 80 years • 1869: Friedrich Miescher (Swiss), identified nuclein , an alkali-soluble material from white blood cells. Nuclein was very large, acidic and rich in phosphorous • Meischer later showed that 10% (by weight) of salmon sperm was nuclein • Nuclein was later renamed nucleic acid DISCOVERY OF NUCLEIN From the pus in the wounds of a dead soldier ( a ), white blood cells ( b ) were taken and their nuclei ( c ) isolated. Nuclein ( d ), a phosphorus- containing organic mixture, was purified from these nuclei. Friedrich Miescher discovered “nuclein” in 1869
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3 Historical perspective (cont.) • Chemicals that stained chromosomes also stained nuclein - treatment with HCl, proteases and alkali removed the staining property - nuclein (nucleic acid) was a component of the chromosome • 1931: Kossel and Levene showed that DNA consisted of repeating molecules containing sugar, nitrogenous bases and phosphate Conundrum of the time: Proteins are more complex than DNA (20 amino acids vs. 4 bases). Therefore, it was thought that proteins must be the genetic material Historical perspective (cont.) • 1928: Frederick Griffith, studying pneumococcus pathogenicity, showed that material could be transferred from a heat-killed virulent strain to a non-virulent strain, making the non-virulent strain virulent. • This process was called
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CH 5 DNA and Chromosomes - 10/19/09 Chapter 5 DNA and...

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