# History of Molecular Biology ## Past Major Discoveries in Molecular Biology - Griffith Experiment (Rough vs Smooth Bacteri) - mice died upon injection with a mxiture of heat-killed S cells and living R cells - Avery Experiment: - Used Trypsin, RNase and DNase to degrade proteins, RNA and DNA respectively - Chargaff’s Experiments (1949) - Used paper chromatography - A fundamental discovery that helped Watson/Crick to identify the true structure of DNA - Hershey-Chase Experiment (1952) - “The Phage Group” were those who believed the predominant theory - The sulfer isotope $S^{35}$ was within the phage capsid proteins while the phosphorus isotope $P^{32}$ - Shows that DNA was - Lucky that phages were used as the capsid remains outside of the cell and can be detached, whereas viruses are capable of entering the cell and would still be detected within the pellet if used in this experiment - Alexander Todd (1952) - The first chemist to synthesize ATP, showed that DNA chains are held together by 3’→5’ phosphodiester bonds (assisted in Watson/Crick) - Watson & Crick (1953) - The first key component of - Kornberg’s Experiment - “How did we discover that DNA strands can separate and synthesize copies?” - Isolated DNA polymerase I and showed that it required energy rich substrates dATP, dCTP, dGTP, and dTTp - shows that DNA grows in the 5’ → 3’ direction - Meselson & Stahl Experiment - Conservative, Semiconservative, and Dispersive > [!note] **Major Takeaways** > > - Scientists went down the wrong path countless times (and sometimes for many decades) before making the discoveries we know today (Ex: The Phage Group) - In 1941, George Beadle and Edward Tatum developed the one gene-one enzyme hypothesis