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  • Explain the roles of the following with the help of an example each in recombinant DNA technology :     (a) Restriction Enzymes      (b) Plasmids   

Explain the roles of the following with the help of an example each in recombinant DNA technology :

    (a) Restriction Enzymes

     (b) Plasmids 

 

 

 

 
 
 
 
 

Answers (1)

a) Restriction enzymes-  Restriction enzymes belong to a larger class of enzymes called nucleases. These are of two kinds; exonucleases and endonucleases. Exonucleases remove nucleotides from the ends of the DNA whereas, endonucleases make cuts at specific positions within the DNA. Once restriction endonuclease finds its specific recognition sequence, it will bind to the DNA and cut each of the two strands of the double helix at specific points in their sugar-phosphate backbones. Each restriction endonuclease recognises a specific palindromic nucleotide sequence in the DNA. 
For example, the restriction enzyme Eco RI isolated from Escherichia coli recognizes the following nucleotide sequence-  

Restriction enzymes cut the strand of DNA a little away from the centre of the palindrome sites, but between the same two bases on the opposite strands. This leaves single-stranded portions at the ends. There are overhanging stretches called sticky ends on each strand. Restriction endonucleases are used in genetic engineering to form ‘recombinant’ molecules of DNA, which are composed of DNA from different sources/genomes. When cut by the same restriction enzyme, the resultant DNA fragments have the same kind of ‘sticky-ends’ and, these can be joined together (end-to-end) using DNA ligases. 


b) Plasmids-  Plasmids are extra chromosomal, autonomous, circular, double-stranded, and self-replicating fragments of DNA present in bacteria and yeast. They are used as vectors in r-DNA technology. They are capable of replicating independently and do not contain any vital genes necessary for bacteria/yeast. They may be responsible for providing pathogenicity to bacteria and yeast. Plasmids may contain the genes for antibiotic resistance. They possess multiple restriction sites. The most commonly used plasmid is pBR322. 
 

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Priyanka Kumari

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