Question

Consider the following table.
$\begin{array}{cc}\text{Column I}& \text{Column II}\\ \text{1) 1928}& \text{A) Hershey - Chase experiment}\\ \text{2) 1933- 44}& \text{B) Griffith`s experiment}\\ \text{3) 1952}& \text{C) Avery, MacLeod, McCarty experiment}\end{array}$
Match the discoveries mentioned above with the correct year.

• A. 1-a, 2-b, 3-c
• B. 1-c, 2-a, 3-b
• C. 1-b, 2-c, 3-a
• D. 1-c, 2-b, 3-a

Answer 1

The correct option is C 1-b, 2-c, 3-a

Griffith discovered the “transforming principle” in 1928.
The bacterial transformation was shown by Frederick Griffith in his experiments on Streptococcus pneumoniae. He took two strains of Streptococcus pneumoniae. They were R(non-virulent)and S(virulent) strains. S-strain was able to cause pneumonia infection in the mouse while R-strain was not. When heat-killed S-strain was mixed with live R-strain, it was able to cause infection in the mouse. He witnessed a miraculous transformation in the bacteria and stated that something was being passed on to the R-strain from the heat-killed S-strain bacteria. Transformation is the genetic alteration of a cell that happens as a result of direct uptake and incorporation of genetic material from the surroundings through the cell membrane.

Avery, MacLeod and McCarty(1933- 44), worked together to identify the biochemical nature of Griffith’s "transforming principle". Their team was the first to observe that DNA is the hereditary material. They treated the purified biochemicals of heat-killed S-strain separately using the enzymes DNase, RNase and proteinase. They observed that when DNase was added, the transformation could not happen (i.e., in the absence of DNA); this indicated that DNA was the transforming principle.

Alfred Hershey and M. Chase (1952), gave unequivocal proof that DNA is the genetic material.
Their experiment proving DNA as the genetic material was based on the principle of transduction. It is the process by which DNA is transferred from one bacterium to another by a virus. They worked with bacteriophages and E.coli bacteria. They found that it was DNA that was getting transferred from bacteriophages into the bacteria by using the radioisotopic technique.