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DNA and Replication

DNA and Replication. Rosalind Franklin. C. T. A. G. Chargaff’s Rule. Adenine must pair with Thymine Guanine must pair with Cytosine The bases form weak hydrogen bonds. DNA. Two strands coiled called a double helix

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DNA and Replication

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  1. DNA and Replication

  2. Rosalind Franklin

  3. C T A G Chargaff’s Rule • Adeninemust pair with Thymine • Guanine must pair with Cytosine • The bases form weak hydrogen bonds

  4. DNA • Two strands coiled called a double helix • Sides made of a pentose sugar Deoxyribose bonded to phosphate (PO4) groups • Center made of nitrogen bases bonded together by weak hydrogen bonds

  5. Phosphate Group O O=P-O O CH2 O N Nitrogenous base (A, G, C, or T) C C Sugar (deoxyribose) C C Three Parts of the DNA Nucleotide

  6. O O P P C O G O P P T A O O P P DNA

  7. Question • If there is 30% Adenine, how much Cytosine is present?

  8. Answer • There would be 20% Cytosine • Adenine (30%) = Thymine (30%) • Guanine (20%) = Cytosine (20%) • Therefore, 60% A-T and 40% C-G

  9. DNA Replication

  10. Replication Facts • DNA is copied in a cell before a cell divides by mitosis, meiosis, or binary fission.

  11. 3’ Parental DNA Molecule 5’ Replication Fork 3’ 5’ DNA Replication • Begins atOrigins of Replication • Two strands open forming Replication Forks (Y-shaped region) • New strands grow at theforks

  12. DNA as a Zipper

  13. DNA Replication • EnzymeHelicaseunwinds and separates the 2 DNA strands by breaking theweak hydrogen bonds

  14. Question • How does the structure of DNA make it easy to copy?

  15. DNA Replication • DNA polymerase (enzyme) adds the new nucleotides • Covalent bonds form between deoxyribose sugar and phosphate group. • Hydrogen bonds between nitrogenous bases.

  16. Zipper Movement

  17. Question • Are the nucleotides of the new sequences of the new strand identical to the original?

  18. 5’ 3’ 5’ RNA Primer DNA Polymerase Nucleotides Synthesis of the New DNA Strands • The Leading Strandis synthesized as a single strand from the point of origin toward the opening replication fork

  19. Leading Strand 5’ 3’ 3’ 5’ DNA Polymerase RNA Primer 5’ 3’ 5’ 3’ Lagging Strand Synthesis of the New DNA Strands • The Lagging Strand is made in MANY short segments It is replicated from the replication fork toward the origin • Leaves gaps in new strand. Gaps filled in by DNA ligase

  20. Replication of Strands Replication Fork Point of Origin

  21. DNA Template Parental DNA New DNA Semiconservative Model of Replication • New DNA consists of 1 PARENTAL (template) and 1 NEW (complementary) strand of DNA

  22. Question • Why is the new strand complementary to the original strand?

  23. Question • After a cell’s DNA is replicated, the cell may divide in two. Each new cell receives one copy of the original cell’s DNA. How are the new strands and the original strands divided between the two new cells?

  24. Explain the statement, “DNA replication depends on specific base pairs”.

  25. Activity: • Is photography a document similar to DNA replication? Think of the original materials, the copying process, and the final products. Explain how the two processes are alike. Identify major differences.

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