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DNA discovery & Structure 8.1 & 8.2
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DNA discovery & Structure 8.1 & 8.2


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  • 2. What is DNA? DNA stands for Deoxyribo Nucleic Acid. DNA carries all of the genetic information for an organism.
  • 3. 1910: Thomas Morgan, through experiments with fruit flies, confirms that chromosomes are the molecules of inheritance.
  • 4. 1928: Frederick Griffith conducts the first genetic experiments on mammals. His experiments dealt with mice and the pneumonia virus. He used two forms: the S form (deadly) and the R form (not deadly). A transforming material passed from dead S bacteria to live R bacteria, making them deadly.
  • 5. 1944: Oswald Avery becomes the first scientist to suggest that DNA was the molecule of inheritance. Before Avery, biologists believed inheritance was controlled by proteins.
  • 6. 1950: Edwin Chargaff determines that certain purines and pyrimidines occur in equal amounts in a DNA strand. This leads to Chargaff’s Rules: the amount of A = the amount of T, and the amount of G = the amount of C. “For every A there is a T, for every G there is a C”
  • 7. 1952: Rosalind Franklin photographs a DNA molecule using an X-ray camera. Her photograph provides evidence that DNA is made of more than a single strand of nucleotides.
  • 8. Franklin’s co-worker, Maurice Wilkins, gives the photograph to a pair of scientists, James Watson & Francis Crick , who are trying to determine the structure of DNA.
  • 9. 1953: Using Franklin’s photo and Chargaff’s Rules, Watson & Crick develop a model of DNA. The model consists of two strands of nucleotides bonded together in the shape of a twisted ladder. This shape is known as the double helix.
  • 10. DNA Structure is the same in all organisms. DNA is a Nucleic Acid (one of the macromolecules [polymers] we learned about during our Biochemistry unit) made up of long chains of nucleotides. Each nucleotide has three parts. phosphate group deoxyribose (sugar) nitrogen-containing base
  • 11. DNA Structure  DNA consists of two strands of nucleotides. DNA looks like a twisted ladder The “backbone” of the ladder is formed by bonds between the...  Sugars (Deoxyribose)  Phosphates. The “rungs” of the ladder are formed by hydrogen bonds between nitrogenous bases. Nucleotide Sugarphosphate backbone Hydrogen bonds
  • 12. 1. Purines: larger bases. There are two purines. A. Adenine (A) B. Guanine (G) 2. Pyrimidines: smaller bases. There are two pyrimidines. A. Cytosine (C) B. Thymine (T) A G C Phosphate T Deoxyribose
  • 13. DNA Structure Each base pair consists of one purine and one pyrimidine. Pairs are bonded by HYDROGEN BONDS Following Chargaff’s Rules , for every Adenine (A) there will be a Thymine (T), and for every Guanine (G) there will be a Cytosine (C). Label your diagram to match this! Nucleotide Sugarphosphate backbone Hydrogen bonds