12.1 Identifying the Genetic Material What is the genetic material? DNA was isolated in 1869, but it wasn’t known to contain genetic material until these experiments…

Vocabulary Vaccine- a substance that is prepared from killed or weakened microorganisms and is introduced into the body to protect the body against future infections by the microorganisms. Virulent- able to cause disease Bacteriophage (phage)- viruses that infect bacteria

Frederick Griffith’s Experiment Year: 1928 What? Made a discovery while trying to prepare a vaccine against the pneumonia-causing bacterium, Streptococcus pneumoniae. Discovered transformation- a change in the phenotype caused when bacterial cells take up foreign genetic material.

Transformation Of Bacteria Two Strains Of Streptococcus Rough Strain (Harmless) Capsules Smooth Strain (Virulent)

Transformation Of Bacteria The Griffith’s 1928 Experiment OUCH! + Control - Control - Control Experimental

Griffith’s Conclusion The harmless bacteria could turn virulent (disease-causing) when mixed with bacteria that cause disease. TRANSFORMATION- process in which one strain of bacteria is changed by a gene of another strand of bacteria. P. 339 in text

Oswald Avery’s Experiments Year: 1944 Experimented in N.Y. City. Found that DNA was the material responsible for the transformation in Griffith’s experiments. There was still doubt that it was DNA, most scientists believed that proteins were the genetic material.

The Hershey-Chase Experiment Time: 1952 Who? Alfred Hershey and Martha Chase Where? N.Y. What? Proved definitely that DNA was the genetic material. Step 1: E. Coli virus’ were grown in radioactive sulfur (S35) in protein and phosphorus (P32) in DNA Radioactive so scientists can easily detect them.

Hershey-Chase Experiment p. 341 in text Step 2 The S phage and P phages were injected into E. Coli bacterium. They were looking at DNA and protein to see what was transferred during reproduction. Step 3 When separated by a centrifuge, the P phage was found in the hosted bacteria (remember step 1: P is in DNA) Step 4 Conclusion-  DNA was reproduced The genetic material is for sure DNA

Using S35 Did protein enter the bacteria? T2 grown in S35 containing media incorporate S35 into their proteins Bacteria grown in normal non-radioactive media T2 attach to bacteria and inject genetic material When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet Mix-O-Matic The supernatant is radioactive, but the pellet is not. Blending causes phage protein coat to fall off Did protein enter the bacteria? Is protein the genetic material?

Using P32 Did DNA enter the bacteria? Is DNA the genetic material? T2 grown in P32 containing media incorporate P32 into their DNA Bacteria grown in normal non-radioactive media T2 attach to bacteria and inject genetic material When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet Mix-O-Matic The pellet is radioactive, but the supernatant is not. Blending causes phage protein coat to fall off Did DNA enter the bacteria? Is DNA the genetic material?