DNA Replication Page 1 of 4 Biology 20 DNA Replication What do the initials DNA stand for? DNA History: 1940's: 1947: Chargaff Chargaff's Rule 1950's: Early 1950's: Rosalind Franklin: X-ray crystallography of DNA 1952: Hershey & Chase: (p. 185; Fig. 10.1) Discovered DNA is the genetic material of bacteriophages (p. 183; Fig. 10.0) Bacteriophages are viruses that infect bacteria (bacteria eaters) Conclusions: viral DNA injected into bacteria, which made more viruses 1953: Watson & Crick: Used information from Franklin's X-ray photos to make a wire scale model Conclusions: Late 1950's: Messelson & Stahl Working with bacteria (E. coli) Confirmed Watson & Crick's model for DNA replication Brief review of DNA structure: DNA is a polymer of? Components of a nucleotide: (p. 186; Fig. 10.2A) a) b) c)DNA Replication Page 2 of 4 Two classes of nitrogenous bases: (p. 187; Fig. 10.2 B & C) a) Purines 1) 2) b) Pyrimidines 1) 2) 3) Which nitrogenous base is only found in RNA? Which nitrogenous base is only found in DNA? Which nitrogenous bases are found in both DNA and RNA? Base pairing of nitrogenous bases (Chargaff's Rule): Purines Pyrimidines Base pairs # of H-bonds Adenine (A) Thymine (T) A = T Guanine (G) Cytosine (C) G = C Adenine comprises 20% of the nitrogenous bases in the DNA of a particular organism. What percentage does cytosine comprise? DNA structure: Double helix - shaped like a ladder (p. 189; Fig. 10.3C) a) Backbone (legs) of the ladder composed of: b) Rungs of the ladder composed of: Double helix: 2 nm, suggested 2 strands 10 nucleotide pairs in each helix turn DNA strands are antiparallel (p. 191; Fig. 10.5B) Why would a cell undergo DNA replication? What phase of the cell cycle does DNA replication take place? (p. 131; Fig. 8.5)DNA Replication Page 3 of 4 DNA Replication (synthesis): Enzymes involved in DNA replication: • helicase, single strand binding protein, primase: • DNA polymerase: a) b) c) • DNA ligase: Origins of replication: (p. 191; Fig. 10.5A) Replication bubble: Eukaryotes: thousands of replication bubbles Why? Replication Fork: (p. 191; Fig. 10.5C) Replication bubble creates a Y-shaped region Replication will spread in both directions: Priming for DNA Replication: Before DNA polymerase can begin work on the daughter strands, a primer must be laid first. Which enzyme produces the primer? What type of molecule is the primer? Synthesis of the new DNA strands: Once the RNA primers are in place, DNA polymerase can go to work. DNA polymerase catalyses the synthesis of the new strands: Direction of synthesis: Why? Leading strand: A different DNA polymerase will come and convert the RNA primer to DNA nucleotides Lagging strand: Okazaki's fragments:DNA Replication Page 4 of 4 Role of DNA ligase: Semi-conservative model for DNA Replication: Watson & Crick suggested & Messelson & Stahl confirmed: DNA template New DNA strand New DNA strand DNA template Proofreading: DNA Repair: Damage to DNA through: Excision repair: DNA Technology: • Recombinant DNA technology: • Polymerase Chain Reactions (PCR): p. 242; Fig. 12.12 • Restriction Fragment Length Polymorphism (RFLP): Restriction enzymes: Use of