- Biotechnology
- Biochemistry
- Microbiology
- Cell Biology
- Cell Signaling
- Diversity in Life Form
- Molecular Biology
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.
Table of Content
Griffith Experiment & Transforming Principle
Griffith experiment diagram, r strain and s strain bacteria.
- Griffith’s Experiment - Transformation in Bacteria
Impact of the Griffith Experiment
Dna as genetic material.
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 s mooth, 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
Also Read : Mendel's Laws of Inheritance
The diagram of griffith experiment is shown below:
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.
Also Read: Genetic Code - Molecular Basis of Inheritance
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:
Also Read : Bacterial Genetics
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.
Also Read : Mutation
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.
Also Read: Difference between Vaccination and Immunization
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.
Also Read: Inherited Traits Lethal Allele - Examples, & its Types Difference Between Phenotype and Genotype Ratio Importance of Variation
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.
Similar Reads
- 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 transfo 8 min read
- DNA as Genetic Material - Hershey And Chase Experiment The Hershey and Chase Experiment, conducted in 1952 by Alfred Hershey and Martha Chase, demonstrated that DNA contains genetic information. They accomplished this by investigating viruses that infect bacteria, known as bacteriophages. In these tests, scientists labelled the virus's DNA with a radioa 7 min read
- Difference Between Translocation and Crossing Over Translocation and Crossing over are both genetic processes that involve the exchange of genetic material between chromosomes. Translocation involves the movement of a chromosomal segment from one chromosome to another during cell division. It often causes genetic abnormalities such as leukemia, infe 6 min read
- Difference between Transformants and Recombinants The difference between transformants and recombinants is that transformants are the cells in which foreign DNA has been introduced, while in recombinants, recombinant DNA from multiple sources is found in the genome. Transformation and Recombination are the two significant steps of DNA cloning. To c 7 min read
- How do the Traits and Characters get expressed? The most fundamental and important aspects of biology are heredity and evolution, which are connected by inheritable features. These two terminologies assist us in learning and comprehending how the life cycle on Earth continues. Both concepts are tied to one another, and there can be no evolution w 8 min read
- What are Some Examples of a Bacterial Infection? Bacterial infections are diseases caused by the rapid bacterial growth in the human body. Bacteria is a single-celled organism that can multiply quickly under favourable conditions. These bacterial infections can affect various parts of the body including skin, gut, lungs, brain, heart, and blood. S 1 min read
- Difference Between Replication And Transcription DNA replication and transcription are two different but related processes that take place inside the cell. Both involve DNA but differ in their role. For example-in replication DNA makes a copy of itself whereas in transcription DNA forms RNA. Both processes are complex as they require a variety of 5 min read
- Difference Between Gram-Positive and Gram-Negative Bacteria Gram-positive and gram-negative bacteria are two major groups of bacteria differentiated on the basis of their structure of the cell wall, and their response to a staining method called the gram stain. The main difference between Gram-positive and negative bacteria is the cell walls because of their 4 min read
- The Experimental Proof Of DNA Replication The process by which cells duplicate their genetic material during cell division—the replication of DNA—was still largely a mystery. This sparked a race to understand how DNA replication happens among several well-known experts. The experimental evidence of DNA replication, which showed that DNA rep 5 min read
- Linkage And Recombination - Principles Of Inheritance And Variation Class 12 NCERT CBSE Class 12- Principles Of Inheritance And Variation- Linkage And Recombination: Linkage and recombination are the phenomena that describe the inheritance of genes. Linkage and Recombination both are related to the genetic information inherited from parents to offspring. Linkage is the tendency of 6 min read
- Genetic Algorithms and Genetic Programming for Advanced Problem Solving Genetic algorithms (GAs) and genetic programming (GP) are branches of evolutionary computing, a subset of artificial intelligence where solutions evolve over time to fit a given set of parameters or solve specific problems. These techniques are inspired by the biological concepts of reproduction, mu 7 min read
- Genetic Code - Molecular Basis of Inheritance CBSE Class12- Molecular Basis Of Inheritance- Genetic Code: The sequence of nucleotides in deoxyribonucleic acid and ribonucleic acid which determines the amino acids sequence of proteins is known as Genetic code. DNA consists of information for protein sequences. RNA consists of four nucleotides: a 5 min read
- Principles of Inheritance and Variation CBSE Notes for Chapter 4 Inheritance is the term given to the process by which characters are passed from parents to offspring which forms the basis of heredity. Heredity is the process of passing down genetic traits from parents to offspring. The degree of difference in characters between a parent and offspring is called v 15 min read
- Eubacteria - Structure, Characteristics, Classification, and Types Eubacteria, also known as true bacteria, are single-celled prokaryotic organisms that inhabit diverse environments and play crucial roles in ecosystems and human health. They belong to the domain Monera. The bacteria belonging to Eubacteria have a rigid cell wall, flagella, and single-cell which lac 8 min read
- Increasing Soil Fertility and Cleaning the Environment - NCERT If we look at the water droplets in a pond under a microscope, we will see many small round structures. These tiny creatures are known as microbes or microbes. They are all around us and are too small to be seen with the naked eye. Microorganisms are classified into four groups: Protozoa: Protozoa a 3 min read
- Difference between Conservative and Semiconservative Replication Conservative Replication and Semiconservative Replication are the two proposed models of replication. In the DNA replication process of conservative replication, the original DNA remains intact and serves as a template for the synthesis of two new DNA molecules. In semiconservative replication, eac 7 min read
- Difference Between Virus And Bacteria The major difference between viruses and bacteria is that viruses are non-living entities composed of genetic material, while bacteria are living single-celled organisms with distinct cellular structures. Viruses and bacteria are microscopic organisms that can cause disease. Understanding the differ 6 min read
- Difference Between Bacteria And Fungi Bacteria and fungi are two different groups of microorganisms that play crucial roles in various ecosystems. While both bacteria and fungi are microscopic and can have significant effects on their environment, both bacteria and fungi are different in terms of cellular structure, life cycles, and eco 3 min read
- Genetic Code and Mutations Genetic code and mutations are important to understand and explain the central dogma of biology. The set of rules governing how DNA sequences are translated into proteins is the genetic code. The four nucleotide bases adenine (A), thymine (T), guanine (G), and cytosine (C), which are organized in pa 5 min read
- School Biology
- School Learning
Improve your Coding Skills with Practice
What kind of Experience do you want to share?
Microbe Notes
DNA Experiments (Griffith & Avery, McCarty, MacLeod & Hershey, Chase)
DNA, deoxyribonucleic acid, is the carrier of all genetic information. It codes genetic information passed on from one generation to another and determines individual attributes like eye color, facial features, etc. Although DNA was first isolated in 1869 by a Swiss scientist, Friedrich Miescher, from nuclei of pus-rich white blood cells (which he called nuclein ), its role in the inheritance of traits wasn’t realized until 1943. Miescher thought that the nuclein, which was slightly acidic and contained a high percentage of phosphorus, lacked the variability to account for its hereditary significance for diversity among organisms. Most of the scientists of his period were convinced by the idea that proteins could be promising candidates for heredity as they were abundant, diverse, and complex molecules, while DNA was supposed to be a boring, repetitive polymer. This notion was put forward as the scientists were aware that genetic information was contained within organic molecules.
Table of Contents
Interesting Science Videos
Griffith’s Transformation Experiment
In 1928, a young scientist Frederick Griffith discovered the transforming principle. In 1918, millions of people were killed by the terrible Spanish influenza epidemic, and pneumococcal infections were a common cause of death among influenza-infected patients. This triggered him to study the bacteria Streptococcus pneumoniae and work on designing a vaccine against it . It became evident that bacterial pneumonia was caused by multiple strains of S. pneumoniae, and patients developed antibodies against the particular strain with which they were infected. Hence, serum samples and bacterial isolates used in experiments helped to identify DNA as the hereditary material.
He used two related strains of S. pneumoniae and mice and conducted a series of experiments using them.
- When type II R-strain bacteria were grown on a culture plate, they produced rough colonies. They were non-virulent as they lacked an outer polysaccharide coat. Thus, when RII strain bacteria were injected into a mouse, they did not cause any disease and survived.
- When type I S-strain bacteria were grown on a culture plate, they produced smooth, glistening, and white colonies. The smooth appearance was apparent due to a polysaccharide coat around them that provided resistance to the host’s immune system. It was virulent and thus, when injected into a mouse, resulted in pneumonia and death.
- In 1929, Griffith experimented by injecting mice with heat-killed SI strain (i.e., SI strain bacteria exposed to high temperature ensuing their death). But, this failed to harm the mice, and they survived.
- Surprisingly, when he mixed heat-treated SI cells with live RII cells and injected the mixture into the mice, the mice died because of pneumonia. Additionally, when he collected a blood sample from the dead mouse, he found that sample to contain live S-strain bacteria.
Conclusion of Griffith’s Transformation Experiment
Based on the above results, he inferred that something must have been transferred from the heat-treated S strain into non-virulent R strain bacteria that transformed them into smooth coated and virulent bacteria. Thus, the material was referred to as the transforming principle.
Following this, he continued with his research through the 1930s, although he couldn’t make much progress. In 1941, he was hit by a German bomb, and he died.
Avery, McCarty, and MacLeod Experiment
During World War II, in 1943, Oswald Avery, Maclyn McCarty, and Colin MacLeod working at Rockefeller University in New York, dedicated themselves to continuing the work of Griffith in order to determine the biochemical nature of Griffith’s transforming principle in an in vitro system. They used the phenotype of S. pneumoniae cells expressed on blood agar in order to figure out whether transformation had taken place or not, rather than working with mice. The transforming principle was partially purified from the cell extract (i.e., cell-free extract of heat-killed type III S cells) to determine which macromolecule of S cell transformed type II R-strain into the type III S-strain. They demonstrated DNA to be that particular transforming principle.
- Initially, type III S cells were heat-killed, and lipids and carbohydrates were removed from the solution.
- Secondly, they treated heat-killed S cells with digestive enzymes such as RNases and proteases to degrade RNA and proteins. Subsequently, they also treated it with DNases to digest DNA, each added separately in different tubes.
- Eventually, they introduced living type IIR cells mixed with heat-killed IIIS cells onto the culture medium containing antibodies for IIR cells. Antibodies for IIR cells were used to inactivate some IIR cells such that their number doesn’t exceed the count of IIIS cells. that help to provide the distinct phenotypic differences in culture media that contained transformed S strain bacteria.
Observation of Avery, McCarty, and MacLeod Experiment
The culture treated with DNase did not yield transformed type III S strain bacteria which indicated that DNA was the hereditary material responsible for transformation.
Conclusion of Avery, McCarty, and MacLeod Experiment
DNA was found to be the genetic material that was being transferred between cells, not proteins.
Hershey and Chase Experiment
Although Avery and his fellows found that DNA was the hereditary material, the scientists were reluctant to accept the finding. But, not that long afterward, eight years after in 1952, Alfred Hershey and Martha Chase concluded that DNA is the genetic material. Their experimental tool was bacteriophages-viruses that attack bacteria which specifically involved the infection of Escherichia coli with T2 bacteriophage.
T2 virus depends on the host body for its reproduction process. When they find bacteria as a host cell, they adhere to its surface and inject its genetic material into the bacteria. The injected hereditary material hijacks the host’s machinery such that a large number of viral particles are released from them. T2 phage consists of only proteins (on the outer protein coat) and DNA (core) that could be potential genetic material to instruct E. coli to develop its progeny. They experimented to determine whether protein or DNA from the virus entered into the bacteria.
- Bacteriophage was allowed to grow on two of the medium: one containing a radioactive isotope of phosphorus( 32 P) and the other containing a radioactive isotope of sulfur ( 35 S).
- Phages grown on radioactive phosphorus( 32 P) contained radioactive P labeled DNA (not radioactive protein) as DNA contains phosphorus but not sulfur.
- Similarly, the viruses grown in the medium containing radioactive sulfur ( 35 S) contained radioactive 35 S labeled protein (but not radioactive DNA) because sulfur is found in many proteins but is absent from DNA.
- E. coli were introduced to be infected by the radioactive phages.
- After the progression of infection, the blender was used to remove the remains of phage and phage parts from the outside of the bacteria, followed by centrifugation in order to separate the bacteria from the phage debris.
- Centrifugation results in the settling down of heavier particles like bacteria in the form of pellet while those light particles such as medium, phage, and phage parts, etc., float near the top of the tube, called supernatant.
Observation of Hershey and Chase Experiment
On measuring radioactivity in the pellet and supernatant in both media, 32 P was found in large amount in the pellet while 35 S in the supernatant that is pellet contained radioactively P labeled infected bacterial cells and supernatant was enriched with radioactively S labeled phage and phage parts.
Conclusion of Hershey and Chase Experiment
Hershey and Chase deduced that it was DNA, not protein which got injected into host cells, and thus, DNA is the hereditary material that is passed from virus to bacteria.
- Fry, M. (2016). Landmark Experiments in Molecular Biology. Academic Press.
- https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Introductory_Biology_(CK-12)/04%3A_Molecular_Biology/4.02%3A_DNA_the_Genetic_Material
- https://byjus.com/biology/dna-genetic-material/
- https://bio.libretexts.org/Bookshelves/Genetics/Book%3A_Online_Open_Genetics_(Nickle_and_Barrette-Ng)/01%3A_Overview_DNA_and_Genes/1.02%3A_DNA_is_the_Genetic_Material
- https://www.toppr.com/guides/biology/the-molecular-basis-of-inheritance/the-genetic-material/
- https://www.nature.com/scitable/topicpage/discovery-of-dna-as-the-hereditary-material-340/
- https://www.biologydiscussion.com/genetics/dna-as-a-genetic-material-biology/56216
- https://www.nature.com/scitable/topicpage/discovery-of-the-function-of-dna-resulted-6494318/
- https://www.ndsu.edu/pubweb/~mcclean/plsc411/DNA%20replication%20sequencing%20revision%202017.pdf
- https://www.britannica.com/biography/Frederick-Griffith
- https://ib.bioninja.com.au/higher-level/topic-7-nucleic-acids/71-dna-structure-and-replic/dna-experiments.html
- https://biolearnspot.blogspot.com/2017/11/experiments-of-avery-macleod-and.html
- https://www.khanacademy.org/science/biology/dna-as-the-genetic-material/dna-discovery-and-structure/a/classic-experiments-dna-as-the-genetic-material
About Author
Prakriti Karki
Leave a Comment Cancel reply
Save my name, email, and website in this browser for the next time I comment.
This site uses Akismet to reduce spam. Learn how your comment data is processed .
IMAGES
VIDEO