Chapter 14- BIOL 151

Chapter 14- BIOL 151

1. Nature of Genetic Material

   • 3 Major Experiments
     • Griffith-1928: Working with S and R type pneumonia causing bacteria
     • Avery, MacLeod, McCarty-1944: Expanded Griffith's experiment, removed other material. showed that DNA transfer caused changes
     • Hershey & Chase- 1952: Experiments with bacteriophages and tagging with isotopes
   • DNA Structure
     • 3 Main Parts
       • Phosphate Group (attached to 5' end)
       • 5-Carbon Sugar
       • Nitrogenous Base
         • Purines
           • Guanine
           • Adenine
         • Pyramidines
           • Thymine
             • Uracil in RNA
           • Cytosine
     • Watson, Crick, Franklin responsible for discovering Helix/Double-Helix structure.

2. DNA Replication

   • Semiconservative Method: Each daughter strand contains one new copied strand and one strand from parent.
     • Proved with Messelson-Stahl Experiment
   • New strand built from 5' to 3' end (reads parent strand 3' to 5')
   • Begins at "replicon". Several A-T bonds which are weaker
     • "origin of replication"
     • DNA gyrase prevents supercoiling
       • a topoisomerase
       • helicase separates the double-helix into two strands
         • SSB proteins bind to single strand to prevent reaction wit surroundings
           • DNA Primase creates primer for attachment of DNA Polymerase
             • DNA Primase is an RNA polymerase because it makes RNA
             • Lagging Strand
               • Requires several primers and is written in fragments
                 • Ozakai Fragments
                   • Stitched together with DNA ligase
               • "Semidiscontinuous"
             • Leading Strand
             • 3 Types of DNA Polymerase
               • Pol III does most of the replication
                 • Beta-clamps keep Pol II attached to strand
               • Pol I removes RNA Primers and writes in DNA
               • Pol I repairs
               • Full organelle is the "Replisome
         • These two together are called the "primosome"