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Unit2 lesson2-dnareplication
 

Unit2 lesson2-dnareplication

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    Unit2 lesson2-dnareplication Unit2 lesson2-dnareplication Presentation Transcript

    • DNA REPLICATION 7.2 P. 146-148
    • REPLICATION OF DNA
      • Before a cell divides it must first make a duplicate of its DNA to ensure that the resulting cell has a complete set of DNA molecules = DNA Replication
      • Enzymes separate or “unzip” the double helix, insert the appropriate bases, and produce covalent sugar-phosphate links while proofreading the whole process
    • More details
      • “ Unzipping” occurs when Hydrogen bonds between base pairs are broken caused by the enzyme DNA polymerase
      • Each separated strand serves as a template for the attachment of complimentary basses.
      • Daughter DNA double helices is composed of one original (conserved) & one newly synthesized strand = semiconservative replication
    •  
    • Messelson and Stahl
      • In 1957, Matthew Meselson and Franklin Stahl did an experiment to determine the best represented DNA replication:
      • Did the two strands unwind and each act as a template for new strands? = semiconservative replication
      • Did the strands not unwind, but somehow generate a new double stranded DNA copy of entirely new molecules? = conservative replication.
    •  
      • In order to determine which of these models was true, the following experiment was performed: The original DNA strand was labelled with the heavy isotope of nitrogen, N-15. This DNA was allowed to go through one round of replication with N-14, and then the mixture was centrifuged so that the heavier DNA would form a band lower in the tube, and the intermediate (one N-15 strand and one N-14 strand) and light DNA (all N-14) would appear as a band higher in the tube.
    • The expected results for each model were: