Question

Transformation experiment was conducted by
(A) Griffith.
(B) Linus Pauling.
(C) Messelson and stahl.
(D) Watson and crick.

Answer 1

Hint:- Term transformation is given to the substance that could be moved from non living cells to living cells, making the living cell show qualities of the non living cell. The transforming principle is used in the search of genetic material by performing experiments on bacteria.

Complete answer:
The transformation experiments directed by Frederick Griffith in 1928,one of the extraordinary bits of proof in building up the idea of hereditary material. He played out the arrangement of tests by choosing two strains of bacterium streptococcus pneumoniae namely S3 and R2.
1.S3 strains are smooth and capsulated types have a mucus coat and produce smooth shiny colonies in the cultural plate. These are virulent and cause pneumonia.
2.R2 strains are rough and non capsulated types have no mucus coat and produce rough colonies. These are non violent and do not cause pneumonia.
The experiment are performed in 4 steps:-(a) S strain:-injected into mice:- Mice die.(b) R strain:-injected into mice:- Mice live.(c) S strain (heat killed):- Mice live.(d) S strain (heat killed) + R strain :- injected into mice:- Mice die.
Griffith was able to kill bacteria by heating them. He observed that heat killed S strain bacteria injected into mice did not kill them. When he injected a mixture of heat that killed S and live R bacteria the mice died. Moreover he recovered living S bacteria from the dead mice. He concluded that the R strain bacteria had somehow been transformed by the heat kill S strain bacteria. This occurred perhaps due to absorption of some transforming principle or substance by rough type bacteria from heat killed smooth bacteria. It had enabled the R strain to synthesise a smooth polysaccharide coat and become virulent.This must be due to the transfer of the genetic material.

So the right answer is (A).

Note:- However the biochemical nature of genetic material was not defined from his experiment. Experiment for biochemical characterisation of transforming principle is done by Avery, MacLeod, and McCarty in 1944.This experiment clearly shows that DNA is the genetic material.