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Or, Were My Genes Really Made by Levi?

What the Heck is DNA?. Or, Were My Genes Really Made by Levi?. James Watson & Francis Crick Cambridge Univ., April, 1953. Frederick Griffith, 1928. Griffith showed that information from dead cells could “transform” live ones. He hypothesizes that it is DNA. Not many believe him.

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Or, Were My Genes Really Made by Levi?

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  1. What the Heck is DNA? Or, Were My Genes Really Made by Levi?

  2. James Watson & Francis CrickCambridge Univ., April, 1953

  3. Frederick Griffith, 1928 Griffith showed that information from dead cells could “transform” live ones. He hypothesizes that it is DNA. Not many believe him.

  4. Hershey & Chase, 1952The “Blender” Experiments.

  5. The Components of DNA • Alpha Helix in the B Form • 4 Bases: Adenine (A), Thymine (T), Cytosine C, and Guanine (G) • Purines: A, and G • Pyrimidines: T, and G • A goes with T, and G goes with C • Deoxyribose and Phosphate make up the sides of the DNA “ladder”

  6. The Bases and the Sugars are flat like steps in a ladder. The Sugars and Phosphates Support the Bases. A Nucleotide Consists of a Base, Sugar, and Phosphate.

  7. Rosalind Franklin and Her Famous X-Ray Diffraction Photo of DNA – Clearly a Double Helix

  8. Three Structures For DNA

  9. Two Hydrogen Bonds Three Hydrogen Bonds

  10. DNA Requires Two Sides For Self-Replication Step 1. The Complementary Sides Separate

  11. Step 2.

  12. Step 3.

  13. Three Alternative Models of DNA Replication

  14. Meselson & Stahl Proved Replication Was Semiconservative

  15. Replication Begins In Many Places At Once

  16. Strands are antiparallel. • Strands run from 5’to3’. • Sugars are held to adjacent ones by phosphodiester bonds. • Nucleotides can only be added to the 3’ end of a chain. • Hydrogen bonds hold the two sides of the ladder together.

  17. Nucleoside Triphosphates Add To The 3’ Ends Only

  18. DNA Polymerase is Restricted To: • Adding Nucleotides to a Pre-existing Chain. • Adding Nucleotides to the 3’ End

  19. Summary of DNA Replication

  20. What’s The Problem With The 5’ Daughter Strand? • The usual replication machinery cannot complete the 5’ end of the daughter DNA strand. • Chromosomes become shorter with every replication and cell division. • Replication stops when the telomere becomes too short.

  21. Replication Mistakes • Errors occur, one in ten thousand base pairs • Errors usually fixed by DNA polymerase • Final error rate is approx. 1 in a billion • U.V. damage is fixed automatically

  22. Some Errors Are Easily Spotted

  23. TELOMERES

  24. Telomerase enxtends the 3’ end so that the 5’ end can reach its full length. Most multicellular organisms lack telomerase. Germ cells and cancer cells have telomerase.

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