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THE DISCOVERY OF DNA FUNCTION AND STRUCTURE DNA FUNCTION Griffith among the 1st scientists to conduct research that would lead scientists to identifying the material responsible for heredity. Used bacteria to help solve this problem. S-strain (virulent) - Coated with mucus and caused pneumonia R-strain (avirulent) - no mucus and did not cause pneumonia Griffith’s Experiment Griffith’s Conclusion These results led Griffith to believe that some material from the S-strain was transferred to the R-strain, which converted the R-strain to s-strain. Transformation - the process during which bacteria are changed by absorbing genetic material from an outside source. Griffith did not know what the transforming factor was. Avery, MacLeod, and McCarthy • Separated cell components (protein, lipid, carbohydrate, RNA, and DNA) • Applied to culture of pneumoncoccus • Identified DNA as transforming factor Hershey-Chase Chase and Hersey used bacteriophages (phages) to prove whether protein or DNA is the genetic material. Hershey-Chase Experiment 1. Radioactive “hot” DNA was put in one group of phages and radioactive “hot” protein was put into another group of phages. 2. The “hot” phages were used to infect the bacteria. 3. Radioactivity was only found in bacteria infected by DNA. 4. Confirmed DNA as the genetic material. Contibutions leading to the discovery of DNA Structure: PA Levine • Identified DNA is composed of: a. phosphate group b. 5-C sugar called deoxyribose c. nitrogenous bases 1. Purines- adenine and guanine 2. Pyrimidines- thymine and cytosine Nitrogenous Bases The nitrogenous bases are divided into two groups. Purines - include adenine and guanine. They have two rings. Pyrimidines - include cytosine and thymine. They are smaller and have only one ring. 1949 Chargraff’s Rules The amount of adenine in DNA is always equal to the amount of thymine. %A = %T The amount of cytosine in DNA is always equal to the amount of guanine. %C = %G Identified that the %ages A/T and G/C differed between species. 1952 Rosalind Franklin and Maurice • Kings College, Wilkins London • X-Ray Crystallography • DNA made of two strands that run in opposite directions (antiparallel) • Phosphate on outside, nitrogenous bases on inside Discover the Structure of DNA The process by which DNA makes copies of itself http://www.youtube.com/watch#v=teV62zrm2P0&fe ature=related 1. Double helix unwinds 2. Hydrogen bonds are broken 3. The two strands break apart, like a zipper 4. New nucleotides begin to attach to the original DNA 5. This will form two new DNA molecules This is semiconservative replication, because each new strand is half comprised of molecules from the old strand. DNA is a code (set of blueprints) for making protein. Protein synthesis is the process that manufactures proteins. RNA Nucleic Acid •Single stranded •4 Bases Adenine Cytosine •Ribose sugar Guanine Uracil