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Enzymes in recombinant DNA technology are used to make specific changes in the DNA molecules that are being manipulated. These enzymes are classified into four categories as follows:

(1) Nucleases: These enzymes are used to cut, shorten or degrade nucleic acid molecules (DNA and RNA). These are of 2 types:

[i] Exonucleases- These remove nucleotide molecules from the end of DNA.

[ii] Endonucleases- These enzymes break internal phosphodiester bonds within DNA or RNA

E.g.: Restriction enzyme or restriction endonuclease, Exonuclease, S1 nuclease, Deoxyribonuclease I (DNase I)

(2) Polymerases: These enzymes are used for making copies of DNA molecules from DNA or RNA template. E.g.: DNA polymerase  I, Reverse Transcriptase

(3) Ligases: These enzymes are used to join DNA molecules. E.g.: DNA ligase, T4 ligase

(4) Modifying enzymes: These enzymes are used to make changes at the end of the DNA molecules by adding or removing chemical groups. E.g.: Polynucleotide kinase, Alkaline phosphatase.

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