Griffith Experiment – Transformation in Bacteria, DNA as Genetic Material

Griffith’s Experiment in 1928 demonstrated bacterial transformation, where non-virulent bacteria turned virulent upon exposure to heat-killed virulent strains. Avery, MacLeod, and McCarty experiment later confirmed in 1944 that DNA, not proteins, was the genetic material responsible for this transformation. Griffith Experiment in conclusion recognized DNA’s significant role in heredity. In this article, we will study the Frederick Griffith Experiment – steps, strain of bacteria, and Griffith Experiment summary.

Griffith Experiment & Transforming Principle

Frederick Griffith conducted an experiment that demonstrated the transfer of genetic information between bacteria. The experiment showed that a heat-killed virulent strain could transform a non-lethal strain of bacteria. Griffith called the material that was transferred the “transforming principle”. Griffith’s experiment involved mixing living non-virulent bacteria with a heat-inactivated virulent form. The bacteria used in the experiment were Streptococcus pneumoniae, which showed two growth patterns. One culture plate had smooth, shiny colonies (S), while the other had rough colonies (R).

Griffith’s experiment proved that some organisms can acquire new properties from their environment and from one another. However, it took almost 20 years for Avery, McLeod, and McCarty to confirm that nucleic acids, not proteins, are the molecules of heredity

Griffith Experiment Diagram

The diagram of griffith experiment is shown below:

R Strain And S Strain Bacteria

The R strain and S strain bacteria are two variants of the bacterium Streptococcus pneumonia, used by Frederick Griffith in his experiment. S strains are pathogenic, meaning they can cause disease. R strains are non-pathogenic, meaning they do not cause disease. Some other differences between R and S strains are:

• Appearance: S strains have a smooth capsule, or outer coat, made of polysaccharides. R strains lack a capsule and have a rough appearance.
• Colonies: S strains produce rough colonies, while R strains produce smooth colonies.
• Virulence: S strains are virulent, while R strains are non-virulent.
• Immune responses: The capsule of S strains allows the cell to escape the immune responses of the host mouse.
• Mice: Mice injected with S strains die within a few days, while mice injected with R strains do not die.

In Griffith’s experiment, when he injected mice with the heat-killed S strain and live R strain, the mice unexpectedly died. This revealed a transformation process where the R strain had taken up genetic material from the heat-killed S strain and become virulent. This observation helped in understanding bacterial transformation and the role of DNA as genetic material.

Griffith Experiment of Transformation in Bacteria

In 1928, English bacteriologist Frederick Griffith conducted an experiment that demonstrated how bacteria can change their function and form through transformation. The experiment was the first to suggest that bacteria can transfer genetic information through transformation. The experiment involved two strains of the bacterium Streptococcus pneumoniae: a virulent (disease-causing) strain (S) and a non-virulent (non-disease-causing) strain (R).

Transformation is the process of one thing changing into another. In molecular biology and genetics, transformation is the genetic alteration of a cell. It’s one of three processes that lead to horizontal gene transfer, along with conjugation and transduction. The detail description of the Griffith’s Experiment – Transformation in Bacteria is as follows:

Griffith Experiment Steps

In the experiment, Griffith injected two types of Streptococcus pneumoniae into mice.

• Griffith then subjected the virulent, smooth strain (S) to heat that killed the bacteria. This heat-killed strain (S) was no longer capable of causing disease.
• Griffith injected mice with the heat-killed virulent strain (S). Surprisingly, the mice survived, indicating that the heat-killed bacteria alone were not harmful.
• Griffith mixed the heat-killed virulent strain (S) with the live non-virulent, rough strain (R) and injected this mixture into mice.
• The mice developed pneumonia and died, even though the strain injected was previously non-virulent.

Observations and Conclusion

Griffith concluded that some factor or biomolecule in the heat-killed virulent bacteria (S) had transformed the live non-virulent bacteria (R) into a virulent form. This phenomenon was termed “transformation,” though Griffith could not identify the nature of the transforming substance.

Significance

Griffith’s experiment laid the groundwork for understanding genetic transformation and proved that DNA, rather than proteins, carried genetic information. This discovery was fundamental to the development of molecular genetics and is also used in a variety of genetic engineering applications.

Impact of the Griffith Experiment

Impact of The Griffith Experiment are:

• Griffith’s experiment led to the discovery of the “transforming principle”. This discovery led to the discovery of DNA as a carrier of genetic information.
• The experiment introduced the concept of genetic transformation, demonstrating that genetic material could alter an organism’s characteristics.
• The understanding of genetic material transfer contributed to advancements in biotechnology, genetic engineering, and recombinant DNA technology.
• Transformation experiments were the basis for proposing the chromosomal theory of inheritance.
• Griffith’s experiment provided how external factors, such as genetic material transfer, could influence the pathogenicity of the bacteria.
• Griffith’s research led to the study of disease prevention and treatment by vaccines and immune serums.

DNA as Genetic Material

Frederick Griffith experiment suggested that a hereditary material from heat-killed bacteria could transform live bacteria. Griffith did not identify the transforming substance. In the 1940s, Oswald Avery, Colin MacLeod, and Maclyn McCarty revisited Griffith’s experiment to identify the transforming substance.

• They isolated cellular components including proteins, DNA, RNA from the heat-killed virulent bacteria (S strain) and tested each component’s ability to transform the harmless bacteria (R strain).
• They used enzymes to selectively break down different cellular components of the heat-killed virulent bacteria (S) to determine which component was essential for transformation.
• They treated the heat-killed virulent bacteria (S) with enzymes that specifically degrade either proteins, RNA, or DNA.
• The treated bacterial extracts were then mixed with live non-virulent bacteria (R), and the mixtures were injected into mice.
• Enzymatic degradation of proteins and RNA did not prevent the transformation. However, when the DNA-degrading enzyme was used, the transforming ability was lost.
• This led Avery, MacLeod, and McCarty to conclude that the transforming substance responsible for genetic transformation in bacteria was DNA.

The discovery revolutionized the understanding of genetics and molecular biology. It established DNA as the molecule responsible for transmitting hereditary information and laid the foundation for the molecular biology. Their research paved the way for subsequent studies that explained the structure of DNA (Watson and Crick, 1953) and contributed to the development of molecular genetics, genetic engineering, and modern biotechnology.

Conclusion – Griffith Experiment

Frederick Griffith’s 1928 experiment on Streptococcus pneumoniae demonstrated bacterial transformation through a transfer of hereditary traits between strains. In Griffith experiment conclusion, the result showed that the harmless R strain could be transformed into a virulent form when exposed to the heat-killed S strain. Subsequent work by Avery, MacLeod, and McCarty in 1944 identified DNA as the transforming substance, establishing it as the genetic material. The discovery laid the foundation for molecular genetics, confirming the role of DNA in transmitting hereditary information.

FAQs on Frederick Griffith Experiment

What was Griffith’s Experiment and Why was it Important?

Frederick Griffith conducted an experiment that suggested bacteria can transfer genetic information through transformation. The experiment was important because it showed that bacteria can change their function and form through transformation.

What is the Griffith Experiment Conclusion?

Frederick Griffith experiment concluded that bacteria can transfer genetic information through a process called transformation.

What was the Most Significant Conclusion of Griffith’s Experiments with Pneumonia in Mice?

Griffith conducted experiments with mice and Streptococcus pneumonia bacteria. He concluded that heat-killed bacteria can convert live avirulent cells to virulent cells. Griffith called this phenomenon transformation.

What did Frederick Griffith Want to Learn about Bacteria?

Frederick Griffith, a British bacteriologist, wanted to learn how bacteria could acquire new traits and how certain types of bacteria produce pneumonia.

How did the Two Types of Bacteria Used by Griffith Differ?

The two types of bacteria used by Griffith were the R strain, lacking a virulent capsule and non-pathogenic, and the S strain, possessing a smooth capsule and causing pneumonia in mice, making it pathogenic.

What was Oswald Avery’s Experiment?

The experiment demonstrated that DNA was the only molecule that transformed from one bacterial strain to another.

What is Griffith’s Transforming Principle?

Griffith performed an experiment with bacteria and mice and discovered that bacteria can incorporate foreign genetic material from their environment, which he called the transforming principle.

Why is Chapter Griffith Experiment Class 12 Important?

The Griffith Experiment in Class 12 biology is important as it describes bacterial transformation, highlighting the role of genetic material in heredity and laying the foundation for modern molecular biology and genetics research.