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DNA

DNA. History Structure Replication. History of DNA. Scientists thought protein was the heredity material Several Scientists disproved this and proved it was DNA :. Griffith. Worked with virulent S and nonvirulent R strain of pneumococcus bacteria

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DNA

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  1. DNA History Structure Replication

  2. History of DNA • Scientists thought protein was the heredity material • Several Scientists disproved this and proved it was DNA:

  3. Griffith • Worked with virulent S and nonvirulent R strain of pneumococcusbacteria • Made the harmless R strain transform into S strain when it took in DNA from the killed S strain.

  4. Hershey & Chase • Worked with radioactively traced bacteriophages (viruses that attack bacteria). • Further proof that DNA was the cell’s genetic material. Radioactive 32P was injected into bacteria!

  5. Chargaff • Developed the base pairing rule by comparing the amounts of A, T, C, G in the cell. • Nucleotide pairing: • Adenine  Thymine • Guanine  Cytosine

  6. Franklin • Took x-ray photographs of DNA • Determined double-helix structure

  7. Watson & Crick • Watson and Crick used Franklin’s x-rays, Chargraff’s rule and developed their model of the DNA molecule (for which they won a Nobel Prize).

  8. Structure of DNA

  9. Shape of DNA • Double stranded, twisted helix, called a double helix • Shape similar to a twisted ladder

  10. Nucleotide Monomers • DNA Nucleotide is the basic unit (monomer) • Made of: • Sugar – Deoxyribose • Phosphate group (PO4) • Base – A T C G (Adenine, Thymine, Cytosine, Guanine)

  11. Phosphate Group O O=P-O O 5 CH2 O N Nitrogenous base (A, G, C, or T) C1 C4 Sugar (deoxyribose) C3 C2 DNA Nucleotide

  12. Polymer Structure • Sides made of phosphate group and deoxyribose sugar • Center (rungs) made of nitrogen bases bonded by hydrogen bonds (A = T and C = G)

  13. Direction of Nucleotides • Each carbon in the sugar is given a number 1’ – 5’ • Sides are antiparallel – one side goes 5’ to 3’ and the other 3’ to 5’ • This determines the direction that it is “read” by enzymes

  14. 5 O 3 3 O P P 5 C G 5 O 1 3 2 4 4 2 1 3 5 O P T A P 3 5 O O 5 P P 3 DNA Macromolecule Structure

  15. Location of DNA • DNA is a large (macro) molecule, and stays in the nucleus

  16. DNA Replication

  17. S Phase of Cell Cycle • DNA must be copied before the cell can divide • Occurs during the synthesis (S) part of cell cycle (before mitosis). S phase G1 G2 interphase Mitosis -prophase -metaphase -anaphase -telophase

  18. 3’ Parental DNA Molecule 5’ Replication Fork 3’ 5’ Helicase enzyme • DNA unwinds and unzips with help of DNA helicases • These enzymes break the hydrogen bonds between base pairs. • This point is called the replication fork.

  19. 5’ 3’ 5’ RNA Primer DNA Polymerase Nucleotide Direction of Replication Polymerase Enzyme • DNA polymerase moves in new nucleotides • Can only add to 3’ end of nucleotide • Follows the base-pairing rule • Two identical DNA strands are formed

  20. Proofreading enzymes • Other enzymes “proofread” the replicated strand looking for errors (mutations). • Incorrect nucleotides are removed and replaced

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