Key Experiments And Identification Of Dna Biology Essay

This essay describes the experiments conducted by Frederick Griffith, Oswald Avery, Alfred D. Hershey and Martha Chase. Besides discuss how the findings of their experiments helped to the designation of DNA as the molecular footing of heritage.

In early 1900 ‘s chromosomes discovered in karyon. The chromosome carries the familial information which passes from parent to offspring. Chromosomes consist of nucleic acid and protein. At those times many scientists believed that protein was the familial stuff. However, later it is found that Deoxyribonucleic acid is the familial stuff. Series of experiments carried out by scientists explains how they discover the ‘transforming rule ‘ , its agent and the heredity stuff.

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In 1928, a British microbiologist Frederick Griffith was made observations with utilizing bacteriums called Streptococcus pneumoniae ( pneumoccous ) which causes pneumonia. Griffith found that, heat killed bacteriums could ‘transform ‘ to a different life bacteriums. Griffith was demonstrated the transmutation experiment utilizing two strains of bacteria. One was the S strain a virulent strain surrounded by polyose coat ( necessary for infection ) produces smooth glistening settlements. The other was R strain a non-virulent strain, produces unsmooth settlements. The R strain was the ‘mutation ‘ of S strain which does non hold any polysaccharide coat and does non do any disease. Griffith was worked with IIS and IIIS strains. S cells can mutate into R cells or R cells can mutate into S cells. Griffith was injected to mice with IIR ( non-virulent ) and IIIS ( virulent ) strains and was reported whether the mice survived or died. First Griffith was injected smooth virulent strain ( IIIS ) and mice died. When the mice were injected with unsmooth non-virulent strain ( IIR ) the mice continued to be healthy. Griffith was injected IIIS bacteriums which killed by heat before injection and the mice stayed healthy. These three experiments showed that the bacteria must alive and must hold a polyose coat to kill the mice. Griffith ‘s 4th experiment was to shoot heat-killed smooth virulent strain assorted with non-virulent unsmooth strain. ( IIR and IIIS heat treated ) Griffith was injected the mixture to mice and the mice died. Populating S bacteriums were found in the mice blood. This was the IIIS type of strain. Griffith theorized that transmutation takes topographic point from IIR to IIIS cells. Griffith believed a protein could be an agent for the alteration in familial stuff and Griffith called the agent the ‘transforming rule ‘ .

In 1930 ‘s and 1940 ‘s Oswald Avery with his colleagues, Colin M. MacLeod and Maclyn McCarty found the agent causes familial transforming is the nucleic acid DNA, non protein. In 1944 they discovered the ‘transforming rule ‘ . Avery and his colleagues studied the transmutation of R-type bacteriums to S-type bacteriums. First they broke unfastened heat treated IIIS bacteriums with detergent to let go of the content of cell. Then they treated the bacteriums with centrifugation which eliminate cellular constituents. ( Cell extract from cellular dust ) . The extract assorted with IIR, incubated and plated on peri-dish. The settlements appeared which shows bacterium has transformed. The scientist knew that the one of constituent ( polyoses, protein, DNA, RNA ) in the extract causes transmutation. To happen out which macromolecular constituent causes transmutation they did enzyme interventions. They degrade polyoses with S111 enzyme and proteins with peptidase enzyme, where the enzyme digests the polyose and protein severally. The transmutation of IIR to IIIS occurred. Transforming rule was either DNA or RNA so ; Avery used the enzyme called nucleases, which degrade nucleic acids. They used ribonucleinase ( RNase ) for RNA, which degrade RNA. The settlements on the home base showed that RNA was non the transforming rule. In the terminal they treated DNA with deoxyribonuclease ( DNase ) which degrades the Deoxyribonucleic acid and no transmutation occurred. These showed that DNA was the familial stuff causes transmutation.

Avery ‘s transmutation experiment was of import because to be able to happen the transforming rule Avery discovered isolation of nucleic acid from bacteriums contaminated by proteins.

In 1953, Alfred Hershey and Martha Chase discovered that Deoxyribonucleic acid is the familial stuff. They studied about bacteriophage ( T2 ) .

The T2 phage infects the E.Coli by attaching to the bacteria ( host cell ) . Then phage releases its familial stuff to the host cell. Bacterial enzymes provide offspring. The host cell so interrupt unfastened, giving out 100-200 phages. Hershey and Chase knew bacteriophage was a virus that infect bacteriums and composed from protein and DNA. They wanted to cognize which substance either protein or Deoxyribonucleic acid made the familial stuff of a bacteriophage so ; they designed experiments to happen out the true constituents. Hershey and Chase prepared two T2 phages one incorporating radioactive Deoxyribonucleic acid and the other incorporating radioactive proteins. To be able to supply radioactive constituents they infected E.Coli with T2. Then they grew E.Coli bacteriums in two civilizations. One media was incorporating radioactive isotope P-32 and the other incorporating radioactive isotope S-35. The bacterium which grown in the P-32 media is radioactively labelled Deoxyribonucleic acid because DNA contains P and the bacterium which grown in the S-35 media is radioactively labelled protein because protein contains sulphur. Each of the two types of radioactively labelled bacteriophage placed into different civilization of bacteriums. The bacteriophages so infected the bacterium. Hershey and Chase used a liquidizer and a extractor to divide the phage ‘s protein parts. ( Protein portion is called phage shade ) The staying portion is infected cell.

In the terminal Hershey and Chase observed the radioactively labelled DNA ( P-32 ) found in host cell and really small found in stage shade. The radioactively labelled protein ( S-35 ) appeared in stage shade and none appeared within the host cell. Therefore, the radioactive protein had non entered the host cells, but the DNA had. The familial stuff passed from parent to offspring. Hershey and Chase proofed that DNA was the familial stuff.

In 1969 Alfred Hershey shared a Nobel Prize with Max Delbruck and Salvador E. Luria “ for their finds refering the reproduction mechanism and the familial construction of viruses ” . ( hypertext transfer protocol: // )

At the terminal of 1920 ‘s the transforming experiment is resulted the formation of transforming rule. Transforming rule, which is discovered by Griffith, helped Avery and his colleagues ( Colin MacLeod and Maclyn McCarty ) to happen that the agent of transforming rule is DNA. Hershey and Chase evidenced that DNA was the heredity stuff and they confirmed DNA ‘s pre-eminent function in genetic sciences. These experiments persuaded the other scientists that DNA entirely was the heredity stuff. This divine James Watson and Francis Crick to get down to detect the construction of DNA. In 1953 Watson and Crick proofed the physical and chemical construction of DNA.


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