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| Artificial Synthesis of DNA |
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| In 1961, Kornberg and his coworkers synthesized DNA from a mixture of deoxyribonucleoside triphosphates, DNA polymerase enzyme, metal ions and a segment of viral DNA functioning as a primer. The synthetic DNA showed biological activity. When introduced into bacteria, this DNA coded one from which primer DNA was taken. |
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| Hargobind Khorana and his colleagues produced the first synthetic DNA in 1965 by purely chemical means. They synthesised the gene coding for yeast alanine tRNA which needed only 77 base pairs. Unfortunately, this gene did not function. Khorana and his associates, in 1979, synthesized the gene coding for tyrosine tRNA of E. coli. This gene had 207 nucleotide pairs. It functioned in combination with a phage DNA. When introduced into E. coli genes responsible for the formation of hormones somatotrophin and insulin have also been artificially synthesized. |
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| Fig. 25.2 - Hargobind Khorana |
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| It refers to small fragments formed by breaking a chromosome of an organism with the help of restriction endonucleases. |
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| Formation of Recombinant DNA |
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| The DNA to be used as passenger or vehicle is isolated from the cell by lysing it with a suitable enzyme. The DNA is then isolated from other cell contents by ultracentrifugation and purified. Both the passenger and the vehicle DNA's are subsequently cleaved by using the same restriction endonuclease so that they have complementary sticky ends. They are mixed under suitable conditions. Their complementary sticky ends pair and their ends are sealed with ligase. This produces a recombinant DNA. |
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