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DNA: The Carrier of Genetic Information

DNA: The Carrier of Genetic Information. Evidence of DNA as hereditary material Proteins—rather than nucleic acids— thought to be genetic material in the 1930s and 1940s Several lines of evidence supported DNA as genetic material DNA is transforming principle in bacteria

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DNA: The Carrier of Genetic Information

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  1. DNA: The Carrier of Genetic Information

  2. Evidence of DNA as hereditary material • Proteins—rather than nucleic acids— thought to be genetic material in the 1930s and 1940s • Several lines of evidence supported DNA as genetic material • DNA is transforming principle in bacteria • Watson and Crick modeled DNA structure

  3. Griffith’s transformation experiments Established that DNA carries necessary information for bacterial transformation

  4. Hershey-Chaseexperiments Established that viral DNA enters bacterial cells and is required for synthesis of new viral particles

  5. Structure of DNA • Regular polymer of nucleotides • Nitrogenous base of purine or pyrimidine • Base covalently links to deoxyribose • Deoxyribose covalently bonds to a phosphate group • Backbone • Alternating sugar and phosphate groups joined by covalent phosphodiester linkages

  6. Nucleotide subunits of DNA

  7. Base compositions in DNA from selected organisms

  8. Structure of DNA molecule • Two polynucleotide chains associated as double helix • Two chains are antiparallel (running in opposite directions)

  9. 3-D model of DNAdouble helix

  10. Base-pairing rules for DNA • Hydrogen bonding between base pairs holds together the two chains of helix • Adenine (A) forms two hydrogen bonds with thymine (T) • Guanine (G) forms three hydrogen bonds with cytosine (C) • Chargaff’s rules • A = T • G = C

  11. Base pairingand hydrogenbonding

  12. DNA Replication • Two strands of double helix unwind • Each strand serves as template for new strand • DNA polymerase adds new nucleotide subunits • Additional enzymes and other proteins required to unwind and stabilize DNA helix

  13. Enzymes involved in DNA replication

  14. Simplified view of DNA replication

  15. Overview of DNA replication

  16. LeadingandlaggingDNAstrands

  17. DNA replication • Bidirectional, starting at origin of replication • Strands replicate at replication fork • Two DNA polymerase molecules catalyze replication • Leading strand • Lagging strand

  18. Bidirectional DNA replication in bacteria and eukaryotes

  19. Replication at chromosome ends • Telomeres • Short, non-coding repetitive DNA sequences • Shorten slightly with each cell cycles • Can be extended by telomerase • Absence of telomerase activity may be cause of cell aging • Most cancer cells have telomerase to maintain telomere length and resist apoptosis

  20. Replicationatchromosomeends

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