Question

Explain transformation experiments conducted by Fredric Griffith. Add note biochemical
characterization of transforming principles.

Answer 1

Hint: Fredric Griffith experiment is also called a transformation principle. He explains that some chemicals transfer from one strain to another. Later on the behavior of these chemicals is explained by three scientists. They named it as a biochemical characterization of transforming principle.

Complete step by step answer: Frederick Griffith performed an experiment in 1928 named Griffith’s experiment. It was one of the first experiments that explain that through the process of transformation bacteria can get DNA. Griffith used two strains of streptococcus pneumoniae. He uses the bacteria to infect the mice, the bacteria have two strains that are virulent (S III) and non virulent (R II). When he injected two strains into mice, he observed that virulent strain bacteria died while the mice infected with non-virulent bacteria survived.
The virulent strain causes pneumonia. Heat killed S- Strain does not produce any symptom of the
disease. At last Griffith injected a combination of live R-type and heat killed S-type bacteria into mice.
Alone bacteria does not show any harmful effects. When injected mixture of two some of the mice
survived while others developed the disease of pneumonia. When the dead mice observed both types of
strains are found in it. Presence of living S-type can only possible if they transformed from R-type nonvirulent bacteria. The phenomenon is called the Griffith effect or transformation.
It proposed that transforming principle is a chemical substance released by heat killing bacteria. It
changed R-bacteria into S-bacteria. It is a permanent genetic change as the new S-type bacteria formed
only S-type progeny.

Note:
In 1944, three scientists named: Avery, MacLeod and McCarty purified biochemicals from the heat killed
S-type bacteria into three components- DNA, carbohydrate and protein. DNA fraction was further
divided into two parts: deoxyribonuclease or DNase and others without it. Addition of these components
was done into the culture tubes containing R-type bacteria. After some time they analyzed the bacterial
population. It is observed that only DNA of S- type can change R-type of bacteria into S-type. Therefore,
It was said that the character or gene of virulence is located in DNA. Thus, they proved that the
a chemical which can be inherited is DNA and it forms the chemical or molecular basis of heredity.