Deoxyribonucleic Acid _DNA_ by ewghwehws


									Deoxyribonucleic Acid
• Frederick Griffith (1928)
   – Did an experiment with bacteria and determined
     there was something in cells that transferred
   – Could be a gene.
• Oswald Avery (1944)
  – Repeated Griffith’s experiment and determined
    that DNA (nucleic acid) transmitted genetic
    information from one generation to the next.
 • Alfred Hershey & Martha Chase (1952)
     – Did an experiment with viruses and
       determined that viruses contain DNA, also.
• DNA (Deoxyribonucleic Acid)
  – Long molecule made up of units called nucleotides.
     • Nucleotides –made up of a 5-carbon sugar (deoxyribose),
       phosphate group, & a nitrogenous base.
     • 4 different nitrogenous bases
         – Purines – Adenine & Guanine (A & G)
         – Pyrimidines – Thymine & Cytosine (T & C)
     • Backbone made up of Sugar & Phosphates
     • Can be joined in any order, so any sequence of bases is
          Composition of DNA
• Long molecule made up of units called
• Nucleotides are made of 3 parts:
 1. *5-carbon sugar (deoxyribose)
  2.*phosphate group
  3.*nitrogenous base (4 different bases.)
      A- adenine
      T- thymime        A always binds T
      G- guanine        G always binds C
• Erwin Chargaff (1930s)
  – Discovered that percentages of Cytosine (C) &
    Guanine (G) were almost equal in all samples
    of DNA
  – Same was true for Thymine (T) & Adenine (A)
• Rosalind Franklin (1950)
  – DNA is a helix – shaped like a coil
  – Might be two strands with the nitrogen bases
    pointing towards the center.
• James Watson & Francis Crick (1970s)
  – Double helix – 2 strands of DNA wound
    around each other like a spiral staircase.
  – Hydrogen bonds form between nitrogenous
    bases that point toward the center.
    • Can only form between certain bases
       – Adenine & Thymine (A-T)
       – Guanine & Cytosine (G-C)
       – Called BASE PAIRING
                Fun Fact
The DNA in a single human cell is more than
 1 meter in length and is found coiled up
 inside the nucleus.
             DNA Replication
• The process where a 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.
• Carried out by the enzyme DNA polymerase
  – Also proofreads the new strands to make sure each is a
    perfect copy of the original DNA.

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