GRIFFITH’S TRANSFORMATION EXPERIMENT 1) Two type of Pneumococcus bacteria : INITIAL OBSERVATIONS: 2) Mouse infected with capsulated bacteria get sick and die 3) Mouse infected with non capsulated bacteria do not get sick & live a) Smooth colonies, cells with capsule b) Rough colonies, cells without capsule 4) Mouse infected with killed smooth (capsule) strain do not get sick & live 5) Mouse infected with 3 & 4 (from above) did get sick and die live bacteria with capsule was found in its blood EXPERIMENTAL FINDING

R cells (no capsule) produce rough colonies S cells (capsule) produce smooth colonies Avery, McLeod & McCarty made extracts from S cells Capsule material Proteins RNA DNA Capsule material Proteins DNA RNA Rough Cells are mixed with one of the extracts from S cells No change Transformation into S type Experiment of Avery, McLeod & McCarty identifies DNA as the transforming molecule

Protein coat DNA PHAGE T2 35 S labeled Protein coat Label remains outside 32 P labeled DNA labeled material found inside infected cell Hersey-Chase Experiment Demonstrating that DNA is the genetic material for phage T2

UTILIZATION OF 15 N & DIFFERENTIAL CENTRIFUGATION TO STUDY REPLICATION MECHANISMS OF DNA E. coli grown in 15 N Upon centrifugation DNA settles near the bottom Heavy E. coli allow to grow one generation in 14 N A second round of replication in 14 N Demonstration of DNA Semiconservative Replication by Meselson & Stahl Upon centrifugation DNA settles in the middle Upon centrifugation DNA settles near the surface and in the middle