DNA_ RNA_ and Protein Synthesis - sfrasca-biology

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					DNA Structure
   L2/3 Biology, 2010-2011




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    What is the Genetic Material?

 Genetic material was thought to be protein until the 1940’s
 Important researchers that proved DNA was the genetic material:
    1928: Frederick Griffith
    1944: Oswald Avery
    1952: Alfred Hershey and Martha Chase
    1952: Rosalind Franklin
    1953: James Watson and Francis Crick
     Big Take Home Message

 These experiments began to prove that DNA, not
 protein, stores and transmits genetic information
 from one generation to the next
                  Franklin

 X-ray diffraction
  photographs of DNA
 Key that provided
  Watson and Crick the
  information to
  finalize their model
  of DNA structure
            Watson & Crick

 1950s, American biologist Watson and British
  graduate student Crick
 Set out to demonstrate the structure of DNA

 Relied on other scientists’ work (Franklin and
  Wilkins) to develop their DNA model
 Received Nobel Prize in Medicine in 1962
           Watson & Crick

 Proposed that DNA is made out of two chains
 that wrap around each other in the shape of a
 double helix
 Explained how DNA could replicate
               Structure of DNA

 DNA = Deoxyribonucleic acid
 Genetic material found in nucleus
 Organic molecule made of P, O, N, C, H atoms
 Monomer = nucleotides, polymer = nucleic acid (DNA)
 Three parts of a nucleotide:
    Deoxyribose (5-carbon) sugar
    Phosphate group
    Nitrogenous base
              Nitrogenous Bases

 4 bases:
     Adenine (A)
     Guanine (G)
     Cytosine (C)
     Thymine (T)
 Bases are like
 rungs of ladder
          Nitrogenous Bases

 Each side of the double helix held together by
  hydrogen bonds between nitrogenous bases
      Sugar-Phosphate Backbone

 Sugar-phosphate
 backbone
    Deoxyribose
    sugar
    Phosphate
 Like the sides of
 a ladder
 Held together by
 covalent bonds
                  Chargraff

 1949, American biochemist
 Observed:
  - percentage of A = percentage of T
  - percentage of C = percentage of G
 Base-pairing rule – A on one strand pairs with T
  on the other, and C pairs with G – pairs of bases
  are called complementary base pairs
  Complimentary Base Pairing

 Order of nitrogenous bases on one side of the
  double helix is complementary to the order of
  bases on the opposite side
 Base-sequence – order of nitrogenous bases on a
  chain of DNA
Q: If a strand of DNA is ATTGCGCGCAT, what’s
  the sequence of the complimentary strand?
A: TAACGCGCGTA
http://learn.genetics.utah.edu/conten
                         t/begin/tour/
        Watch “What is DNA?” by clicking the button on
                                    the top of the page




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http://www.pbs.org/wgbh/nova/gen
            ome/program_adv.html
          Watch “Instructions for a Human Being”




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