Question

Read the following statements and choose the appropriate option
Statement 1 - In Griffith’s experiment, when mice were injected with heat-killed R-strain and live S-strain the mice survived.
Statement 2 - In the Hershey-Chase experiment radioisotope of phosphorus - ${}^{32}P$ was incorporated into the DNA of the viruses.
Statement 3 - In the experiment conducted by Avery, MacLeod and McCarty, they found out that in the presence of RNAse enzyme transformation of the bacteria took place.

• A. Statements 1 and 2 are correct, but statement 3 is wrong
• B. Statements 1 and 3 are correct, but statement 2 is wrong
• C. Statements 2 and 3 are correct, but statement 1 is wrong
• D. Statements 1, 2 and 3 are correct.

Answer 1

The correct option is C Statements 2 and 3 are correct, but statement 1 is wrong

In 1928, Griffith concluded that some transforming principle (a chemical substance) from the heat-killed, smooth S-strain virulent bacteria had entered the living, rough R-strain non-virulent bacteria and transformed the latter into virulent bacteria which in turn led to the death of the mouse due to pneumonia infection.
In the Hershey and Chase experiment, radioactive phosphorus (${}^{32}P$) and radioactive sulphur (${}^{35}S$) were used to culture bacteriophages. The DNA of bacteriophage was radiolabeled with ${}^{32}P$ and protein with ${}^{35}S$.
These radiolabeled bacteriophages were then made to infect E. coli cells. It was seen that the bacterial cells contained radioactive viral DNA (${}^{32}P$), but not radioactive viral protein(${}^{35}S$). This means that the bacteriophages transferred their DNA to the E. coli bacteria.
Hence this experiment proved that the DNA, and not protein, is the genetic material passed from the virus to bacteria.
In 1944, Avery, McCarty and MacLeod discovered that RNA - digesting enzymes (RNases) and protein-digesting enzymes (proteases) did not affect transformation. So, the transforming substance was not an RNA or protein.
Digestion with DNase inhibited transformation. This is how they concluded that DNA is the hereditary material.