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DNA and DNA Replication
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  1. DNAandDNA Replication Used and Modified with permission from Robert Goodman, Biology Department,Citrus Community College

  2. DNA see link for more on discovery • Discovery of the DNA double helix A. 1950’s B. Rosalind Franklin- X-ray photo of DNA.

  3. DNA • Discovery of the DNA double helix A. 1950’s B. Rosalind Franklin- X-ray photo of DNA. C. Watson and Crick- described the DNA molecule from Franklin’s X-ray.

  4. Question: • What is DNA?

  5. Deoxyribonucleic Acid (DNA) • Made up of nucleotides (DNA molecule) in a DNA double helix. • Nucleotide: 1. Phosphate group

  6. Phosphate Group O O=P-O O DNA Nucleotide

  7. Deoxyribonucleic Acid (DNA) • Made up of nucleotides (DNA molecule) in a DNA double helix. • Nucleotide: 1. Phosphate group 2. 5-carbon sugar

  8. Phosphate Group O O=P-O O 5 CH2 O C1 C4 Sugar (deoxyribose) C3 C2 DNA Nucleotide

  9. Deoxyribonucleic Acid (DNA) • Made up of nucleotides (DNA molecule) in a DNA double helix. • Nucleotide: 1. Phosphate group 2. 5-carbon sugar 3. Nitrogenous base • ~2 nm wide

  10. 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

  11. A or G T or C Nitrogenous Bases • PURINES 1. Adenine (A) 2. Guanine (G) • PYRIMIDINES • 3. Thymine (T) • 4. Cytosine (C)

  12. A T BASE-PAIRINGS Base # of Purines Pyrimidines PairsH-Bonds Adenine (A)Thymine (T) A = T 2

  13. 3 H-bonds G C A T BASE-PAIRINGS Base # of Purines Pyrimidines PairsH-Bonds Adenine (A)Thymine (T) A = T 2 Guanine (G)Cytosine (C) C G 3

  14. C T A G Chargaff’s Rule • Adeninemust pair with Thymine • Guanine must pair with Cytosine • Their amounts in a given DNA molecule will be about the same.

  15. Question: • If there is 30%Adenine, how much Cytosine is present? Answer: Adenine (30%) = Thymine (30%) Guanine (20%) = Cytosine (20%)(50%) = (50%) There would be 20%Cytosine.

  16. 5 O 3 3 O P P 5 5 C O G 1 3 2 4 4 2 1 3 5 O P P T A 3 5 O O 5 P P 3 Antiparallel Double Helix

  17. “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone DNA Double Helix

  18. Information Information is contained in the linear sequence of the bases in the polynucleotide chain. DNA from all organisms has the same structure, but different sequence = different information A+T or G+C are different for different species. (Chargaff’s rules)

  19. View DNA Movie

  20. Question: When and where does DNA Replication take place?

  21. S phase DNA replication takes place in the S phase. G1 G2 interphase Mitosis -prophase -metaphase -anaphase -telophase Synthesis Phase (S phase) • S phase in interphase of the cell cycle. • Nucleus of eukaryotes

  22. DNA Replication: Basic Concept After separation, each parental strand becomes a template Each “daughter” molecule has one parental strand and one new strand. Complementary pairing Replication is semiconservative

  23. Synthesis of new DNA • New DNA is synthesized by adding one nucleotide at a time • The nucleotide comes in as a triphosphate • Depending on which one is needed, it could be dATP, dTTP, dGTP or dCTP

  24. Bases are added using DNA polymerase to the 3’ end of the growing strand DNA polymerase catalyzes this reaction

  25. DNA Synthesis in both Strands • Enzyme only works from 5’  3’ • Antiparallel: • (one goes 5’ 3’, the other goes 3’  5’). • New synthesis has to go in opposite directions. 5’ 3’ 3’ 5’

  26. Origins of Replication Replication Forks: • Hundreds of Y-shaped regions of replicating DNA molecules where new strands are growing.

  27. Copying by Two Mechanisms Continuous Discontinuous

  28. DNA replication starts from a specific origin Bubbles form!

  29. Origin of Replication • A particular sequence of nucleotides on the DNA that serves as the signal for the starting point of DNA replication. • The number varies depending on the size of the DNA.

  30. We can see these bubbles!

  31. Okazaki Fragments

  32. DNA Template New DNA Parental DNA DNA Replication • Semiconservative Model: 1.Watson and Crick showed: the two strands of the parental molecule separate, and each functions as a template for synthesis of a new complementary strand.

  33. DNA Repair • Excision repair: 1. Damaged segment is excised by a repair enzyme (there are over 50 repair enzymes). 2. DNA polymerase and DNA ligase replace and bond the new nucleotides together.

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

  35. 5 O 3 3 O P P 5 5 C O G 1 3 2 4 4 2 1 3 5 O P P T A 3 5 O O 5 P P 3 Remember!!!!!

  36. 3’-CGCATAC-5’ Question: • What would be the complementary DNA strand for the following DNA sequence? DNA 5’-GCGTATG-3’