Question

The transforming substance in Griffith's experiment is

• A. protein
• B. DNA
• C. mRNA
• D. polysaccharide

Answer 1

The correct option is B DNA

The transforming principle in Griffith's experiment is DNA. Griffith conducted an experiment in 1928. In this experiment he chose two strains of Stephylococcus pneumoniae bacteria. One of them was a smooth strain which was virulent and the other one was a rough strain which was non-virulent. The smooth strains caused pneumonia when they were injected to the mice, and the rough strains did not cause pneumonia in mice. Griffith heat killed the smooth strain bacteria and injected them into mice and he observed that pneumonia was not caused in them. He mixed the heat killed smooth strain and rough strain and injected the mixture into mice and this mixture caused pneumonia in mice. When he tested the blood of the mice, he saw both rough and smooth strains of bacteria. This implied that some factor from the dead smooth bacterial strain had taken entry into the rough strains and converted them into smooth strains. He called this factor as Transforming principle.

Later in 1944 scientists, Avery, MacLeod, and McCarty conducted an experiment to find out what the transforming principle was, They selected DNA, Proteins and RNA. They eliminated proteins by adding proteases and the strains were able to perform the transformation, they eliminated RNA with RNase the strains were still able to perform the transformation, they eliminated DNA with DNase and now the smooth strains lost the ability to transform Rough strains and hence it was proved that the DNA was the transforming principle.

Therefore the right option is option B, DNA.