Molecular Biology of the Gene DNA

Identification of Genetic Material Identification of Genetic Material Structure of DNA Structure of DNA DNA Replication DNA Replication

Genetic Material –DNA or Protein? Bacteriophage Replication 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

Hershey and Chase Experiment

Bacterial Transformation Frederick Griffith, 1928 Diplococcus pneumoniae infects mice Diplococcus pneumoniae infects mice Mice develop pneumonia and die Mice develop pneumonia and die Two types of bacteria: R bacteria rough coat  no pneumonia R bacteria rough coat  no pneumonia S bacteria smooth coat  pneumonia S bacteria smooth coat  pneumonia Coat type is associated with virulence. 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 Polymers are made up of monomers Mono = one Mono = one Poly = many Poly = many For example: For example: Proteins are made up of amino acids

Polynucleotides Polynucleotides are made up of nucleotides Polynucleotides are made up of nucleotides Sugar-phosphate backbone Phosphate group Nitrogenous base Sugar DNA nucleotide DNA polynucleotide DNA nucleotide Sugar (deoxyribose) Thymine (T) Nitrogenous base (A, G, C, or T) Phosphate group A C T G T T G T C A

Basic Structure of a Nucleotide Phosphate Group Nitrogenous Base Sugar

Nitrogenous Bases (DNA) Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines One Ring Purines Two Rings

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" 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 ( )Watson and Crick with their model of DNA

Rope Ladder Model

Sugar and Phosphate Backbone Nitrogenous Base Pairs Rope Ladder Model

Complementary Base Pairs A-T A-T G-C G-C

DNA: The Double Helix Hydrogen bond Base pair Ribbon model Partial chemical structure Computer model G C TA A T T A C C G G G C T T T T A A A A GC A T A C T G CG A T

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 Structure of DNA DNA Replication DNA Replication DNA vs. RNA DNA vs. RNA

Chromosomes and Mitosis

Chromosomes Are Made of DNA

DNA Replication DNA Replication is Semiconservative DNA Replication is Semiconservative Parental molecule of DNA Both parental strands serve as templates Two identical daughter molecules of DNA T Nucleotides CG A GC A A T T A A A A C C C T T G G A C A A A A A A CC C CG T G T T T T G T T T G G Each new double helix contains one parental strand and one daughter strand

G C T A A T G G C C T T A A C C G G G G C C G G G C C C T T T T T C A A A A A G T G C A T T T T A A A A

An enzyme “unzips” DNA Replication Bubble

Origin of replication Bubble Parental strand Daughter strand Two daughter DNA molecules Replication Bubbles

3 end 5 end 3 end P 4 A T C G HO OH P P P P P C G P P A T P DNA is synthesized from 5 ’ to 3 ’ One Little Problem…

DNA polymerase molecule Parental DNA LEADING STRAND Daughter strand synthesized continuously LAGGING STRAND Daughter strand synthesized In pieces DNA Polymerase Can Only Move 5 ’ to 3 ’ DNA polymerase adds nucleotides to the 3 ’ end “ase” = enzyme

DNA Ligase 3 5 DNA ligase 3 5 LEADING STRAND LAGGING STRAND DNA ligase “glues” the fragments together

Structure of DNA Structure of DNA DNA Replication DNA Replication DNA vs. RNA DNA vs. RNA

Nitrogenous Bases (DNA and RNA) Thymine (T) Cytosine (C) Adenine (A) Guanine (G) H Uracil (U) Pyrimidines One Ring Purines Two Rings

DNA vs. RNA Deoxyribonucleic Acid Ribonucleic Acid H OH Phosphate Group Ribose Phosphate Group Deoxyribose Nitrogenous Bases TCAG UCAG Nitrogenous Base CH 3 H Thymine Uracil