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Molecular Biology of the Gene. DNA. Identification of Genetic Material Structure of DNA DNA Replication. Genetic Material –DNA or Protein?. Bacteriophage Replication. Martha Chase and Alfred Hershey (1952). Roles of the Genetic Material.
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Identification of Genetic Material • Structure of DNA • DNA Replication
Genetic Material –DNA or Protein? Bacteriophage Replication Martha Chase and Alfred Hershey (1952)
Roles of the Genetic Material “A genetic material must carry out two jobs: duplicate itself and control the development of the rest of the cell in a specific way.” -Francis Crick
Bacterial Transformation Frederick Griffith, 1928 • Diplococcus pneumoniae infects mice • Mice develop pneumonia and die Two types of bacteria: • R bacteria rough coat no pneumonia • S bacteria smooth coat pneumonia • Coat type is associated with virulence.
Griffith’s Experiments Figure 9.1
The “Transforming Principle” • Avery, MacLeod, and McCarty, 1944 • Treated lysed S bacteria with protease and DNase • DNase prevented transformation • Therefore DNA is the transforming principle Figure 9.2
Monomers and Polymers • Polymers are made up of monomers • Mono = one • Poly = many • For example: Proteins are made up of amino acids
Polynucleotides • Polynucleotides are made up of nucleotides Sugar-phosphate backbone Phosphate group A Nitrogenous base A Sugar Nitrogenous base (A, G, C, or T) C C Phosphate group DNA nucleotide T T Thymine (T) G G Sugar (deoxyribose) T T DNA nucleotide DNA polynucleotide
Basic Structure of a Nucleotide Phosphate Group Nitrogenous Base Sugar
Nitrogenous Bases (DNA) Cytosine (C) Adenine (A) Guanine (G) Thymine (T) Purines Two Rings PyrimidinesOne Ring
And the Nobel Prize Goes To… • Physiology or Medicine 1962"for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material" Rosalind Franklin (1920-1958) Watson and Crick with their model of DNA
Rope Ladder Model Sugar and Phosphate Backbone Nitrogenous Base Pairs
Complementary Base Pairs • A-T • G-C
DNA: The Double Helix C G T A Hydrogen bond T A Base pair T A G C G C G C A T C G C G T A A T A T T A T A G C A T Computer model Ribbon model Partial chemical structure
Orientation of DNA The 5’ phosphate of one nucleotide is attached to the 3’ hydroxyl group of the previous nucleotide The directionality of a DNA strand is due to the orientation of the phosphate-sugar backbone Figure 9.11
Structure of DNA • DNA Replication • DNA vs. RNA
T A T A T T T A A A C G C G C G C G G C G C G C G C G C C A T A T T T A A A A T A T T T A A Nucleotides Parental molecule of DNA Both parental strands serve as templates Two identical daughter molecules of DNA DNA Replication • DNA Replication is Semiconservative Each new double helix contains one parental strand and one daughter strand
G C A T G C C G A T T A G C A T C G G C C G G C C C G A C A G T A T T G T T G T A A T A A A T C A T T A
An enzyme “unzips” DNA Replication Bubble
Parental strand Origin of replication Daughter strand Bubble Two daughter DNA molecules Replication Bubbles
3 end 5 end P HO 5¢ 2¢ 4¢ 3¢ A T 3¢ 1¢ 1¢ 4¢ 2¢ 5¢ P P P C G P P C G P P T A OH P 3 end 5 end One Little Problem… DNA is synthesized from 5’ to 3’
DNApolymerase molecule 3¢ 5¢ LEADING STRAND Daughter strand synthesized continuously Parental DNA 5¢ 3¢ LAGGING STRAND Daughter strand synthesized In pieces 3¢ 5¢ DNA Polymerase Can Only Move 5’ to 3’ DNA polymerase adds nucleotides to the 3’ end “ase” = enzyme
5¢ 5¢ 3¢ 3¢ DNA ligase DNA Ligase LEADING STRAND LAGGING STRAND DNA ligase “glues” the fragments together
Structure of DNA • DNA Replication • DNA vs. RNA
H Uracil (U) Nitrogenous Bases (DNA and RNA) Cytosine (C) Adenine (A) Guanine (G) Thymine (T) Purines Two Rings PyrimidinesOne Ring
Nitrogenous Bases U C A G DNA vs. RNA Ribonucleic Acid Deoxyribonucleic Acid Nitrogenous Base Phosphate Group Nitrogenous Base Phosphate Group H CH3 Uracil Thymine Deoxyribose Ribose OH H Nitrogenous Bases T C A G