Practice question

Oswald Avery, Colin MacLeod, and Maclyn McCarty in 1944 purified transforming principle from heat-killed S pneumococci. They sequentially removed lipids, polysaccharides, and proteins with enzymes, showing activity remained after protease and RNase treatments but was abolished by deoxyribonuclease. Chemical analysis revealed DNA with high viscosity, phosphorus content, and diphenylamine reaction positive. Transformation of rough to smooth required intact DNA, proving DNA rather than protein carries genetic specificity. This milestone established DNA as genetic material preceding Hershey-Chase confirmation and transformed molecular biology understanding.