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12-2 Chromosomes _amp; DNA Replication

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12-2 Chromosomes _amp; DNA Replication Powered By Docstoc
					DNA Replication

     Chromosomes &
     DNA Replication


Foothill High School Science Department
         DNA & Chromosomes
• DNA Location
  – Prokaryotes – Cytoplasm
    • Single Circular Molecule


  – Eukaryotes – Nucleus
    • Multiple Chromosomes
       – Humans 46
       – Drosophila 8
       – Giant Sequoia 22

             Foothill High School Science Department
                    DNA Length
• E. coli (Gram Neg. Bacilli)
       4,639,221 Base Pairs
   1.6 mm long which must fit in
     a bacteria 1.6 um wide, or
     1/1000 the length of the
     DNA strand
• Human DNA 1000 times
  larger
• Tightly Packed

               Foothill High School Science Department
       Chromosome Structure
        Each Human Cell Contains
        More Than A 6 feet of DNA

• Tightly Packed Into Chromatin
     DNA + Protein = Chromatin
     DNA Coiled Around Proteins Called Histones
       –Forms Beads Called Nucleosomes


            Foothill High School Science Department
         Chromosome Structure
• Nucleosomes pack together to form a thick fiber
  containing loops and curls




                    Usually loose, diffuse
              Condense during Mitosis & Meiosis
      Fold enormous lengths of DNA into the tiny nucleus

              Foothill High School Science Department
Chromosome Structure
                                      Histones

                             proteins that have very low
                               mutation rates


                             Appears most mutations
                               have been lethal –
                               therefore, eliminated


                             Regulate “reading” of
                               chromosome
  Foothill High School Science Department
             DNA Replication
• Watson & Crick Discovered
  – Structure of DNA
  – How DNA can be copied &
    replicated.
  – Each strand of DNA is a
    mirror image of the other
    strand
     • Strands are
      Complimentary

            Foothill High School Science Department
               Duplicating DNA

                    Replication
Duplication of the DNA in preparation for cell division
                ( S phase of Interphase )

                        Prokaryotes
  Replication starts at a single point and proceeds in opposite
                              directions
                        Eukaryotes
  Occurs at multiple points on multiple chromosomes at once

               Foothill High School Science Department
             Duplicating DNA
Key Concept:
  During DNA replication, the DNA molecule
    separates into two strands, then produces
    two new complementary strands following
    the rules of base pairing. Each strand of the
    double helix of DNA serves as a template,
    or model, for the new strand



            Foothill High School Science Department
     How Replication Occurs
     Carried out by enzymes
  That unzip the molecule of DNA
        Break the hydrogen bonds
         between the base pairs

Each strand is a template for the new strand


          Foothill High School Science Department
DNA Replication




  Foothill High School Science Department
       How Replication Occurs
• Original DNA

                      TACGTT
                      ATGCAA
• Unzipped




             Foothill High School Science Department
      How Replication Occurs
Replicated:

          TACGTT                 ATGCAA
          ATGCAA                 TACGTT

        Remember – Base Pairing


         Foothill High School Science Department
  How Replication Occurs
Enzymes Involved Named For The
     Reactions They Catalyze

          DNA Polymerase
 1) Polymerizes individual nucleotides
 2) Proof Reads each new DNA strand



       Foothill High School Science Department
DNA Polymerase




Foothill High School Science Department

				
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posted:5/7/2013
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