Lecture outline (pages 278-291)

DNA structure, replication and repair

• How do we know that DNA is the genetic material?
  • Frederick Griffith and Oswald Avery- experiments with pathogenic and non-pathogenic bacteria
  • Hershey and Chase- bacteriophage T2 experiments
• Structure of DNA (deoxyribonucleic acid)
  • 3 components- nitrogenous base (adenine, cytosine, guanine, thymine), pentose sugar (deoxyribose), phosphate group
  • double helix, with sugar-phosphate chains on the outside and nitrogenous bases on the interior
  • A=T base pairing, G=C base pairing
  • A, G are purines (2 organic rings), C,T are pyrimidines (one organic ring)
• Replication of DNA
  • double helix is separated and each strand is copied, semi-conservative replication
  • new nucleotides are added by DNA polymerase in order to copy the old (template) strand of DNA
• DNA repair
  • "proofreading" by DNA polymerase
  • excision repair

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