Question

In his transforming experiment on mice, Griffith has taken two strains of streptococcus pneumonia, R-stain and s-strain. In which of the following case mice will remain alive?

• A. Heat killed s-strain + R-strain + proteases injected into mice
• B. Heat killed S-strain + R-strain + Rnases injected into mice
• C. Heat killed S-strain + R-strain + Dnases injected into mice
• D. DNA from heat killed S-strain + R-strain injected into mice

Answer 1

Answer: (C)

Heat killed S-strain + R-strain + Dnases injected into mice

• In Griffith's experiment, the mice were injected by both S (smooth Streptococcus)and R (rough Streptococcus) strains of the bacteria.

1) S strain → Injected into mice → Mice developed pneumonia and die.

2) R strain → Injected into mice → Mice live.

3) Heat-killed S strain → Injected into mice → Mice live. (heat kills the bacteria).

4) Heat-killed S strain + R strain → Injected into mice → Mice die.

• DNA, RNA and proteins were extracted from the heat-killed S strain bacteria.
• The treated the heat-killed S strain with proteases to break down proteins and were also treated the strain with RNAses and then DNAses to break down RNA and DNA molecules respectively.
• The treatment of the S-strain with the protease and RNAse treatments did not affect the transformation of the R strain into the virulent one.
• The treatment with DNAses inhibited the transformation of the R strain thus, it was concluded that DNA was the genetic material.
  
• So, the correct answer is 'Heat killed S-strain + R-strain + Dnases injected into mice'.