Question

1. Griffith, 1928 2. Avery, MacLeod, & McCarty, 1944 3. Hershey and Chase, 1952 For each experiment, answer the following questions: 1. What was the purpose of the experiment? 2. Explain the experimental design. What technology was critical to the experiment? What were the different groups in the experiment? Why was each one included? 3. What were the results (or predicted results) of the experiment? 4. What did they conclude from the experiment?

Answer 1

Previously protein was the genetic material and not DNA. Some direct evidance for proving DNA will be the genetic material was derived from the experiments of

1.Frederick Griffith 1928

2.Avery,macleod and McMart's 1944

3.Hershey and Chase 1952

Griffith experiment:

1. Experiment on bacterial transformation

2.Studied Diplococcus pneuminae

Strain :SIII: Virulent, had Lipopolysaccharide capsule, caused pneumonia to the mice, kill the mice.

growth on culture plate: smooth colonies

Strain :RIII: avirulent, lacked lipopolysaccharide capsule

growth on culture plate: rough colonies

Strain Serotype	Colony	Capsule	Virulance
SIII	Smooth	Present	Present
RII	Rough	Absent	Absent

Experiment

1) RII type strain - injected to mice - mice lived

2)SIII strain - injected to mice- mice died

3) Heat killed S type - injected mice - mice survived

4)Heat killed S type + RII - injected mice- mice died

5) Heat killed SIII + RII+ DNase enzyme- injected mice- mice survived

6) Heat killed SIII+RII+Protease enzyme - injectted mice- mice died

In step 4 whille coinjecting Heat killed S and R he found injected mice got pneumonia and die, while isolating baecteria from this dead mice he found it is Virulent.

3) He interpreted that some factor transfered the dead avirulent R II starin to SIII.

4) Further from experiment 5 , shows DNA as the genetic material no transformation as DNase digest DNA and no transformation in experiment 6.

2.Avery,macleod and McMart's

1)Experiment on transformation

2) Extract of SIII + RII+ DNase enzyme- injected mice- mice lived

Extract of  SIII + RII+ Protease enzyme- injected mice- mice survived

Extract of SIII + RII+ RNase enzyme- injected mice- mice survived

3) Only Dnase distroyed the transforming substance hence transforming substance is DNA.

3.Hershey and Chase

1) Experiment on T-Even 2,4 bacteriophage

Thry were studying on bacteriophage. They wanted to isolate the phage substance. Since virus composed of a protein coat and genetic materail they labelled each with different isotope. Genetic material or DNA labelled with radiocative phosphorus 32 because phosphorus was only present in the DNA not in protein. Radioactive sulphur 35 used to label Protein coat because sulphur was abscent in DNA.

The experiment repeated for both Sulphur labeled and phosphorus labeled phages.

• When the bacteria was infected with the phage the resultant progeny contained radioactive isotopes in their structure.
• The labeled progeny were made to infect bacteria.
• Seperation of phage coat which remained on the outersurface of the bacteria was done by agitation followed by centrifugation.
• Bacteria lysed to release phage progeny. Progeny of phage labeled with P32 remained labeled, whereas progeny of S35 were unlabeled.
• They showed phage is resistant to DNase enzyme.
• They showed protein protected DNA from DNase, but once seperated phage become inactive,DNase will hydrolyse DNA.

3) They concluded from the above experiment that DNA not protein is the genetic material.