3.1.5.2 DNA Replication

3.1.5.2 DNA Replication

1. Genome

   • Collective of all the DNA in a cell
   • PROK
     • Loop of naked DNA and plasimids
   • EUK
     • Nucleus, Mitochondria and Chloroplasts (plants)
       • Cell replication
         • Binary fission
         • Mitosis

2. Mitosis

   • S Phase
     • Replication of DNA
   • G2
     • replication of Chloroplasts and Mitochondria DNA
   • G1
   • Interphase
     • Everything BUT Mitosis

3. DNA

   • 23 Pairs of chromosomes
   • If DNA was a language
     • Genes would be paragraphs
       • Chromosomes would be books

4. Process of DNA Replication

   • 1) Unwinding DNA
     • Gyrase
   • 2) Unzipping DNA
     • DNA Helicase
   • 3) Synthesis new strand
     • DNA Polymerase
     • 1.Free activated nucleotides align + H-bond to complementary base
     • 2. DNA Polymerase catalyses the addition of bases in the 5'-3' direction
       • Bases are added to the 3' end of the new strand
     • 3. Condensation of activated nucleotides joining the nucleotides together by phosphodiester bonds
     • 4. Joining of fragments of lagging strand by ligase enzyme

5. Activated nucleotides?!

   • Nucleotide w/ 3 phosphate groups attached
   • Hydrolysis of 2 phosphate groups provide energy for the bond between nucleotides
     • Energy ∴ provide energy for DNA synthesis
   • ATP, CTP, GTP, TTP
   • DNA replication = active process

6. Semi-conservative replication

   • Conserve half and the molecules and the other half is new
   • PROK
     • Form a bubble w/the daughter strands in it
   • Mutations
     • 1 in10⁸ bases
     • doesn't necessarily harmful
   • Meselsohn + Stahl had 3 facts to prove semi-conservative replication
     • 1) All bases in DNA contain nitrogen
     • 2) ¹⁴N isotope is lighter than ¹⁵N isotope
     • 3) Bacteria must incorporate N from their growing medium into any new DNA
     • Experiment
       • (1) Firstly they grew bacteria in ¹⁵N
         • (2) Extract a sample of the DNA (control)
           • (3) Extract bacteria
             • (4) Put in ¹⁴N medium
               • (5) remove sample after 1st round of replication
                 • (6) 2nd sample removed after 2nd round of replication
                   • (7) Take 3rd sample after 3rd replication
           • 2.1 Extract the DNA
             • 2.2 Suspend in CSCl
               • Allows DNA to float @ different depths depending on its density
               • 2.3 Centrifuge
                 • Allow different layers to separate

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