DNA Replication

DNA Replication

1. Cell Division

   • Nuclear division
     • Cytokinesis
       • Follows ND and is where the whole cell divides
     • The nucleus divides via mitosis or meiosis

2. There are four requirements:

   • Both strands of DNA molecules act as a template for the attachment of these nucleotides
     • The enzyme DNA polymerase
       • A source of chemical energy is required to drive the process

3. Phosphate- deoxyribose backbone

   • The rungs are the nitrogenous bases
     • Repeating units of of the deoxyribose sugar and phosphate group
       • A phosphodiester bond occurs- two bonds One at the 5’ of one nucleotide One at the 3’ of another nucleotide
   • Easy to dismantle and pull apart DNA molecule
     • Good for replication and it can reform

4. Conservative replication

   • The OG DNA remain intact and separate daughter DNA copy was built from new molecules
   • Of the two molecules produced, one would be made of entirely new material while the other would be OG material

5. Functions

   • It is thermally stable and can withstand high temperatures
     • It has a rigid backbone structure of a pentose sugar and a phosphate this protects the bases
       • DNA molecules held in position by hydrogen bonds and disulfide bonds which allows large amounts of dna to be stored in a small space
     • Base pairs can be easily split by enzymes to allow replication to occur

6. Meselson-Stahl experiment

   • 15N only = the heavy dna from e-coli grown exclusively in 15N forms a band near the bottom of the tube
     • 14N only = the light dna from e-coli grown exclusively in 14N forms a band near the top of the tube
   • 15N- 14N = 1st gen dna from e-coli grown for one generation in 14N forms a band midway between the heavy and light bands
     • This intermediate dna contains one strand with 15N and one strand with 14N
     • 15N- 14N = 2nd gen dna from e-coli grown for two generations in 14N forms two bands
       • Intermediate dna is from the first generation, whereas light dna is from the second generation

7. The enzyme DNA helicase breaks the hydrogen bonds linking the base pairs of DNA

   • Double helix separates into its two strands and unwinds
     • Each exposed polynucleotide strand then acts as a template
       • Complementary free nucleotides bind by specific base pairing
         • This forms the missing polynucleotide stand on each of the two original polynucleotide strands of DNA
           • Each of the new DNA molecules contains one of the original DNA strands
             • Half the original DNA has been saved and built into each of the new DNA molecules
               • This is semi conservative replication