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Bio102: Introduction to Cell Biology and Genetics The Double Helix Key Terms: nucleotide 5’ end 3’ end antiparallel base base-pairing complementary phosphate deoxyribose phosphodiester bond purine pyrimidine helix sugar-phosphate backbone bacteriophage transformation proteinase nuclease Key Questions: Why did many researchers originally believe that genes were probably made of protein? As you know, all amino acids contain an NH2 group...why couldn't Hershey and Chase have used radioactive nitrogen instead of radioactive sulfur to track the bacteriophage protein? Why is it important to the overall structure of DNA that a pyrimidine always pairs with a purine? A dideoxy nucleotide looks just like a regular nucleotide, except that it has no -OH group on its 3' carbon. What would happen if DNA polymerase inserted a dideoxy nucleotide into a DNA chain? Lecture Outline: How do we define a gene? Griffith Experiment R and S Streptococcus pneumoniae dead S cells can transform R cells to make them virulent Avery, McCarty, MacLeod Experiment treated dead S cells with RNase, DNase or Proteinase DNase treatment blocked the ability to transform the R cells therefore, DNA must be the genetic material Hershey and Chase Experiment radioactively labeled protein or DNA in a bacteriophage only the radioactive DNA got into the host cell. Therefore, DNA must be the genetic material Watson and Crick (and Franklin and Wilkins) determine DNA structure. Implies function nucleotides are composed of a base (G, A, T, or C) and a deoxyribose sugar A and G are purines; C and T are pyrimidines polymer of nucleotides joined by sugar-phosphate linkages distince 5’ and 3’ ends, based on the deoxyribose sugar base-pairing (G to C and A to T) holds two strands together in an antiparallel arrangement noncovalent hydrogen bonding in three dimensions, the strands wrap around each other in a double helix