Unit 7 DNA Replication Mitosis and Cancer

Unit 7 DNA Replication Mitosis and Cancer - Structure of...

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Structure of DNA 13.1-13.3 In the fall and winter of 1952 and 1953, 22-year-old James Watson and 35-year-old Francis Crick pulled together 50 years of work of many other scientists and figured out the structure of deoxyribonucleic acid, DNA. They proposed that if their structure was correct, it could replicate itself and act as the genetic material . In 1962, they were awarded with the Nobel Prize.
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What was known before Watson and Crick? Griffith’s Experiments Evidence that some factor within cells could transform other cells and is heritable . Study : make a vaccine for pneumonia. Method : two strains of bacterium Streptococcus pneumoniae on mice ( Mus musculus ). Result : transformation of bacterium was permanent and heritable . This result was evidence of….
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What was known before Watson and Crick? Avery and McCarty’s Experiments Evidence that transforming principle could not be carbs, lipid or protein. DNA may be the transforming principle. Not protein? Study : identify the transforming principle. Method : isolate S. pneumoniae cell contents and systematically destroy each biomolecule. Result : cell contents with only DNA remaining could still transform S. pneumoniae from harmless to deadly.
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What was known before Watson and Crick? The Hershey-Chase Experiments Evidence that DNA, not protein, is the genetic material of viruses. Study : Do viruses use DNA, protein, or both to replicate themselves? Method : radioactively label sulfur and phosphorus in separate treatments of a bacteria virus and follow their movements. Result : sulfur stayed on the outside of bacterium but phosphorus was injected in .
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DNA’s Building Blocks Scientists knew the components of DNA long before Watson and Crick. Erwin Chargaff , for example, had been studying the DNA nucleotide composition of the cells of organisms for over a decade. A nucleotide is a nucleic acid monomer consisting of a five-carbon sugar (deoxyribose), three phosphate groups , and one of four nitrogen-containing bases . DNA consists of four nucleotide building blocks Two pyrimidines : thymine and cytosine Two purines : adenine and guanine
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But Chargaff didn’t “connect the dots”
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Chargaff is now credited with two major contributions to biology: Chargaff’s Rules Rule 1 - The amounts of thymine and adenine in DNA are the same, and the amounts of cytosine and guanine are the same: A = T and G = C. Rule 2 - The proportion of adenine and guanine differs among species. This molecular diversity among species helped establish DNA as a more credible candidate for the genetic material than protein. Observed Percentages of Bases in Six Organisms Source of DNA A T G C Human ( Homo sapiens ) 31.0 31.5 19.1 18.4 Mouse ( Mus musculus ) 29.1 29.0 21.1 21.1 Frog ( Rana pipiens ) 26.3 26.4 23.5 23.8 Fruit Fly ( Drosophila melanogaster ) 27.3 27.6 22.5 22.5 Corn ( Zea mays ) 25.6 25.3 24.5 24.6 E. coli 24.6 24.3 25.5 25.6
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Unit 7 DNA Replication Mitosis and Cancer - Structure of...

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