Biology Investigatory Project - 2024-25 - Chandroday Public School - PDF

# Chandroday Public School ## Investigatory Project File on Griffith Experiment - Exploring Bacterial Transformation **Affiliation to C.B.S.E.** **Affiliation No.** - 3330391 **Subject:** Biology **Session:** 2024-25 **Submitted To:** Miss. Sakshi Tiwari **Submitted By:** Bhrigma Chandrakar ##...

# Chandroday Public School ## Investigatory Project File on Griffith Experiment - Exploring Bacterial Transformation **Affiliation to C.B.S.E.** **Affiliation No.** - 3330391 **Subject:** Biology **Session:** 2024-25 **Submitted To:** Miss. Sakshi Tiwari **Submitted By:** Bhrigma Chandrakar ## Certificate It is hereby certified that BHRIGYA CHANDRAKAR, a student of Class - XII 'A', has successfully completed research on the topic "Griffith Experiment - Exploring Bacterial Transformation" under the guidance of Miss. Sakshi Tiwari during the academic year 2024-25. **External Examiner:** Name: **International Examiner:** Miss. Sakshi Tiwari **Principal:** Mr. Naveen Kumar ## Acknowledgement I would like to express my deepest gratitude to everyone who played a part in bringing this project to fruition. Special thank you goes to Miss. Sakshi Tiwari, my teacher for their invaluable guidance and unwavering support throughout the entire process. Their insights and suggestions helped shape my ideas and conduct the necessary experiments. I am also incredibly thankful to my parents for their unconditional support and encouragement. Their unwavering belief in my abilities has always spurred me on to strive for excellence. Accidentally I would like to acknowledge the immense help and contributions of my friends and classmates. They readily share their ideas and provide assistance whenever needed, making an enormous impact on the successful completion of this project. ## Griffith Experiment - Exploring Bacterial Transformation ### Aim The aim of the Griffith experiment conducted in 1928 by Frederick Griffith, was to investigate the process of bacterial transformation. Specifically Griffith sought to determine whether a non-virtual strain of streptococcus phenomoniae could be transformed into a virulent from when exposed heat killed virulent bacteria. This experiment aimed to uncover the nature of the genetic material responsible for the transformation. Griffith findings laid the groundwork for understanding the role of DNA in heredity, ultimately contributing to the field of molecular genetics and our comprehension of genetic information transfer in organisms. ### Introduction The Griffith experiment conducted in 1928, marked is significant milestones in genetic and molecular biology. Frederick Griffith studying strains of bacterium streptococcus phenomoniae: a virulent rough strain (S) that caused pneumonia and a non - virulent rough strain (R) that did not. To investigate the properties of these strains, Griffith injected mice with different combinations of live and heat-killed bacteria. When he injected mice with the live strain they remained healthy. However, when he injected them with the heat killed S strain the mice also survived. The surprising result occurred when he combined heat-killed S bacteria with live R bacteria; the mice developed pneumonia and died. ### R & S Strain Bacteria * Stretococcus pneumonia comes in several types of strains, Griffith chooses two different strains for his experiments. * One strain of bacteria has a smooth surface and is known as smooth strain (S strain), while the other has a rough surface and is known as the rough strain (R strain). * Bacteria of the S train have a smooth surface because they produce a polysaccharide protective coating that forms the outermost layer. * Apart from the morphological differences, Griffith discovered another significant difference between the S and R strain of the bacteria,i. e., the S strain is the "virulent "strain capable of causing death in mice, where as the R strain is the "non-virulent " strain that will not cause death in mice. Griffith observed that when he injected these bacteria into mice, the mice infected with the virulent S strain died from pneumonia, whereas the mice injected with the non-virulent R strain survived. ### Griffith's Transformation Experiment * Griffith was researching the possibility of developing a pneumonia vaccine. * He used two strains of pneumonia (streptococcus pneumonia) bacteria that infected mice - a virulent (causing disease) S (smooth) strain and a non - virulent type R (rough) strain. * The S strain produced a polysaccharide capsules that protected itself from the host's immune system, resulting in the host's death, whereas the R strain lacked that protective capsule and was defeated by the host's immune system. * Griffith attempts to inject mice with heat-killed S bacteria as a part of his research (i.e., S bacteria that had been heated to high temperatures, causing the cells to die). The heat - killed S bacteria, but unsurprisingly, did not cause disease in the mouse. When harmless R bacteria were combined with harmless heat killed bacteria and injected into a mouse, the experiments took an unexpected turn. * Not only did the mouse develop pneumonia and die, but Griffith discovered living S bacteria in a blood sample taken from the dead mouse. He concluded that some factor or biomolecules from the heat - killed S bacteria had entered the living R bacteria, allowing them to synthesize a polysaccharide coating and become virulent. * As a result, this factor "transformed" the R bacteria into S bacteria. * Griffith called this factor the, "transforming principle" concluded that it carried some material from the S bacteria to the R bacteria. * This process is now known as bacterial transformation and is used in a variety of significant genetic engineering applications. ### Oswald Avary - MacLeod - Mc Carty. Experiment During World war II, in 1943 Oswald Avery, maclyn McCarty, and Colin MacLeod worked at Rockefeller University in New York, decided themselves to continuing the work of Griffith in order to determine the biochemical nature of Griffith transforming principle in earn in vitro system. They used the phenotype of S. Pneumonia self express on blood agar in order to figure out whether transformation had taken place order 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 cells 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 wear 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 IIS 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 IIS cells, that helps to provide the distinct phenotype 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, 8 years after in 1952, Alfred Hershey and Martha chase concluded that DNA is the genetic material. Their experiment tool was bacterio pages- viruses that attack bacteria which are specifically involved in the infection of Escherichia coli with 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. T2 phage consists of only protein (on the outer protein cost) and DNA (core) that could be potential genetic material to instruct E. coil to develop it's pregnancy. They experimented to determine protein or DNA from viruses entered into the bacteria. * Bacteriophage was allowed to grow on two of the mediums: one containing a radioactive isotope of phosphorus (32p) and the other containing a radioactive isotope of sulphur (35s). * Phages group on radioactive phosphorus (32 P) contains radioactive P labeled DNA (not radioactive protein) as DNA contains Phosphorus but not sulphur. * Similarly, the viruses grown in the medium contain radioactive sulphur (35 S) containing radioactive5S labelled protein(but not radioactive DNA) because sulphur is found in many proteins but is absent from DNA. * E. coils were introduced to be infected by the radioactive phages. * After the progression of injection, the blender was used to remove the remains of page and phage parts from the outside of the bacteria, followed by centrifugation in order to separate the bacteria from the phase debris. Centrifugation results in the setting 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 radio activity in the palate and supernatant in both media, P was found in large amounts in the palate while. S in the supernatant that is palate contain radioactively P labelled infected bacterial cells and supernatant was enriched with radioactivily S labelled 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. ### Impact of Griffith experiment The Griffith Experiment significantly impacted genetics and microbiology, and its findings have had far-reaching implications from modern medicine and biotechnology. Some of the key impacts of the experiment include: * **Discovery of DNA as the genetic material:** The experiment provided the force evidence for the transfer of genetic material from one bacterium to another and have laid the foundation for the discovery of DNA as a genetic material. This discovery has had a major impact on the advancement of genetics and has had to shape our understanding of the role of genetics in determining an organisms characteristics. * **Understanding of bacterial virulence:** The experiment helped to shed light on the nature of bacterial virulence and the mechanism by which bacteria can cause disease. This has led to the development of new treatment for bacterial infections and has had a major impact on medical microbiology. * **Advancements in genetic engineering:** The discovery of DNA as the genetic material and understanding of the mechanism by which it can be transferred between organisms have paved the way for developing genetic engineering techniques. These techniques have revolutionised the biotechnology field and have had a major impact on medicine, agriculture, and other industries. * **Development of vaccines:** Understanding the mechanism by which bacteria causes disease and the role of genetic material in determining bacterial virulence has led to the development of new vaccines. These vaccines have helped to control and prevent the spread of many bacterial diseases and have had a major impact on public health.