1. 16A Intro to DNA

2. Science as a process What was the genetic material? At the time, most scientists believed it was protein.

3. Griffith Mouse Experiment (1928) Living S Living R Heat Killed S Heat Killed S/Living R Transformation: change caused by dead pathogenic cells. Avery (1944): Concluded that ______ was the transforming agent, still viewed with skepticism.

4. Hershey/Chase (1952) DNA is the genetic material of T2 bacteriophage. – Bacteriophage: _______ that infects __________. – T2: phage that infects E Coli, turns it into a T2 producing factory. Question: was it DNA or protein of the T2 that was causing the reprogramming? – Radioactively labeled: ___________: found in proteins only. Mixed T2 with E Coli, blended and centrifuged, found that the pellet of bacteria cells were not radioactively labeled but the supernatant viral parts were. ___________: found in DNA only. Mixed T2 with E Coli, blended and centrifuged, found that the pellet of bacteria cells was labeled and the supernatant was not. CONCLUSION:

5. Chargaff Base Pairing Rules Already known that DNA is a nucleotide containing sugar (deoxyribose), phosphate and a nitrogenous base (adenine, thymine, guanine and cytosine). Chargaff found a characteristic ratio of bases in all species Number of adenines = number of _________ Number of cytosines=number of _________ Chargaff’s base pairing rules:

6. The Current Model The race to the 3-D structure of DNA was won by Watson and Crick. – Used X-ray crystallography from Franklin and Wilkins to determine the size and double helix shape – Used wire model, chemistry (hydrophobic bases on interior) to create the double helix model. – Used size and Chargaff’s rules to determine A to T (2 Hydrogen bonds) and C to G (Three hydrogen bonds) – Correct width (see page 298) – Adenine and Guanine are purines: two rings – Thymine and Cytosine are pyrimidines: one ring

7. Structure