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DNA

DNA. Biology 11: Chapter 7. Discovery of DNA Function. A. Discovery of DNA 1. first isolated from cells in 1868 2. unknown function B. Griffith Experiments (1928) 1. worked with a pneumonia-causing bacteria 2. two strains R strain: non-fatal S strain: fatal.

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DNA

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  1. DNA Biology 11: Chapter 7

  2. Discovery of DNA Function A. Discovery of DNA 1. first isolated from cells in 1868 2. unknown function B. Griffith Experiments (1928) 1. worked with a pneumonia-causing bacteria 2. two strains R strain: non-fatalS strain: fatal

  3. 3. experiment: mice injected with a. R (rough) cells - lived b. S (smooth) cells - died c. heat killed S cells - lived d. heat killed S cells + live R cells - mice died !! 4. analysis of last group showed live S cells and no R cells

  4. So What did that Mean? • Transformation of R cells into S cells meant that some Genetic Material must have gone from into the R-cells from the S. • Source of Genes: protein or nucleic acids

  5. Hershey-Chase Experiment 1. Was DNA or proteins the genetic material? 2. Bacteriophages - viruses used a. protein coat b. nucleic acid interior (DNA core)

  6. 3. Radioactive labeling of protein & DNA

  7. 4. Results showed that DNA directed the formation of new viruses, not the protein coat

  8. Discovery of DNA Structure Components of DNA 1. DNA consists of a sugar, base and phosphate group 2. one of 4 possible bases: adenine (A) Purines guanine (G) cytosine (C) Pyrimidines thymine (T)

  9. DNA Structure – The Twisted Ladder

  10. The Nucleotide: • Sugar • Phosphate Group • Nitrogenous Base Phosphate Base Ribose Sugar

  11. Experiments - 1949 1. the amount of A = amount of T 2. the amount of C = amount of G 3. ratios vary by species

  12. X-Ray experiments • Used X-rays to examine structure of DNA • Observed that a. DNA is helical b. DNA exists in long strands c. DNA is highly repetitive

  13. Watson-Crick analysis 1. Constructed a model of DNA structure 2. Phosphate groups from backbone 3. Double-stranded molecule 4. Base=pairing of A-T and G-C 5. Helical shape

  14. DNA Replication & Repair A. Replication 1. replication is semi-conservative 2. major molecules a. helicase - unwinds DNA strands b. DNA polymerase - copies DNA c. DNA ligases - seal newly formed DNA strands

  15. Semi-Conservative Replication of DNA - each half is duplicated = semi-conserved - new DNA molecule is clone of old one because the new strand must match the base pairs of the old one!

  16. B. DNA Repair 1. DNA polymerase “proofreads” the new strands 2. DNA ligases help to repair mismatched bases

  17. DNA Organization A. Chromosome structure 1. DNA is organized into long molecules called chromosomes 2. chromosome are stabilized by proteins called histones 3. histones organize the DNA

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