DNA Replication pt1

Cards (52)

  • Nucleic acids
    Molecules that play a general role in organisms
  • DNA
    Deoxyribonucleic acid
  • RNA
    Ribonucleic acid
  • Nucleic acids as information molecules

    They carry genetic information
  • DNA structure
    • Double helix
    • Anti-parallel
    • Complementary base pairing
    • Base pair hydrogen bonds
    • Phosphodiester bonds
  • Griffith's experiment showed that a non-virulent bacterium could be transformed into a virulent form
  • Avery, MacLeod & McCarty's experiment pointed to DNA, not protein, as the hereditary material
  • Hershey & Chase's experiment using radioactive labeling showed that DNA is the hereditary material
  • Chargaff determined that the DNA proportions are always A = T, G = C
  • Franklin, Watson & Crick used X-ray diffraction and model building to determine the structure of DNA
  • Meselson & Stahl's experiment using density labeling showed how DNA replicates
  • DNA replication in prokaryotes
    1. Single-stranded binding proteins
    2. Helicase
    3. DNA polymerase III
    4. DNA polymerase I
    5. Primase
    6. DNA ligase
  • Semi-discontinuous replication
    Leading and lagging strands, Okazaki fragments, proofreading
  • Prokaryotic and eukaryotic DNA replication have general similarities and differences
  • In 1856-1863, the molecule that transmits hereditary information was unknown at the time of Mendel
  • DNA discovered by Friedrich Miescher
    1869
  • Miescher's study revealed that DNA is made up of a phosphate group, a pentose sugar, and a nitrogenous base
  • Griffith's experiment showed that traits (virulence) could be passed from dead to live bacteria, but the transmitting molecule was unknown
  • Avery, MacLeod & McCarty's experiment determined that DNA, not protein, was the hereditary material
  • Hershey & Chase's experiment using radioactive labeling proved that DNA, not protein, is the genetic material in bacteriophages
  • Chargaff determined the consistent ratios of DNA nucleotides (A=T, G=C)
  • Bacteriophages
    Viruses that infect bacteria
  • Chase use bacteriophages to prove that DNA is the hereditary molecule
  • Protein
    Molecules that have sulfur, but no phosphorus
  • DNA
    Molecules that have phosphorus, but no sulfur
  • Hershey and Chase use bacteriophages to prove that DNA is the hereditary molecule

    1952
  • Protein use a radioactive isotope (35S)
  • DNA use a radioactive isotope (32P)
  • When the virus protein is tagged with a radioactive element, the tag doesn't transfer to the bacteria
  • When the virus DNA is tagged with a radioactive element, the tag transfers to the bacteria
  • Erwin Chargaff found the matching proportion of nucleotides: 30% Adenine, 30% Thymine, 20% Cytosine, 20% Guanine
  • Chargaff's rules
    The proportion of A = the proportion of T, The proportion of C = the proportion of G
  • Chargaff discovered the nitrogenous base pairing, but did not figure out the structure of DNA
  • Rosalind Franklin
    • She was a researcher in the Wilkins Lab and produced the first good DNA X-ray crystallography
    • X-Ray diffraction technique needs a solid with regular, repeating units of atoms (crystal)
  • DNA X-Ray crystallography
    • Purine + Purine diameter > 2 nm
    • Pyrimidine + Pyrimidine diameter < 2 nm
    • Purine + Pyrimidine diameter = 2 nm
  • Watson and Crick
    • They solved the structure of DNA based on Franklin's patterns and Chargaff's rules
    • They developed the first molecular model of DNA (1953)
    • Rosalind Franklin did not receive a Nobel prize, since she died of cancer in 1958 (possibly caused by her exposure to X-ray)
  • Complementarity of bases
    Adenine (A) can form two hydrogen bonds with Thymine (T), Guanine (G) can form three hydrogen bonds with Cytosine (C)
  • DNA replication
    1. Semiconservative model
    2. Conservative model
    3. Dispersive model
  • The experiment of Meselson and Stahl proved that the semiconservative model is the correct model of DNA replication
  • Based on the structure of DNA, Watson and Crick suggested a semi-conservative DNA replication mechanism