A.Discovery of “transformation” – a change in genotype and phenotype due to the uptake of external DNA by a cell 1.Griffith 1920s did experiments with Streptococcus pneumoniae (p294 fig16.2) a.took two strains of S. pneumoniae, one virulent, one not
b.heat killed virulent strain, then mixed them with the living nonvirulent strain c.living nonvirulent strain became virulent
d.nonvirulent strain took on virulent strain’s DNA became virulent e.see p294 fig16.2 S strain = virulent, R = nonvirulent
f.eventually Griffith’s work lead way to more studies on DNA being the carrier of genetic info.
B.Proof that viral DNA and not viral protein contains genetic information to make more viral particles 1.Hershey and Chase 1950s p295 fig16.4
a.knew that viruses could infect bacteria and make more viruses using the host cell’s replicating ‘machinery’ b.background: sulfur gets incorporated into virus’ protein/phosphorus into virus’ DNA c.took T4 (bacteriophage) and plated with a lawn of E. coli and radioactively labeled sulfur, result = T4 with radioactive labeled protein (DNA not labeled) d.took T4 and plated with E. coli and radioactively labeled phosphorus = T4 with radioactively labeled DNA (protein not labeled) e.background: when virus + bacteria is spun down, viral particles in supernatant and bacteria in pellet f.took T4 (S-labeled) infected new E. coli lawn, spun down, found S-radioactive labels in supernatant g.took T4 (P-labeled) infected new E. coli lawn, spun down, found P-radioactive labels in pellet h.result = it’s the DNA that’s injected into the host to make more virus (even plated these spun down pellet bacteria, and they lysed and released new virus
C.Discovery of the structure of DNA
1.Watson and Crick
a.used an x-ray crystallography picture (p297) by Franklin to determine DNA as a double-helical structure b.review p298 – A pairs with T and G with C/ A and G are purines and C...