Enzymes worn in biotechnology or r-DNA Technology

DNA ligase enzyme- A type of enzyme used to seal the cut ends of DNA  fragments. It is a type of molecular adhesive used during joining of desired gene with suitable vector DNA. DNA ligase was first discovered by Dr. Khorana from T4 bacteriophages and thus named as T4-ligase.
Endonuclease enzyme- It is a tiny biological scissor used to cut foreign DNA and plasmid DNA before they are allowed to form recombinant DNA. It occurs naturally in some bacterial cells and acts as chemical weapon against the invading bacteriophages. It cuts both the strands of double stranded DNA and occurs in solution form.
Most of the restriction endonuclease enzyme a specific palindromic sequence for producing cuts and they usually show sticky end type cutting. The existence of restriction enzyme in bacterial cells was first demonstrated by Arber. (1906) in Haemophilus influenzae and named as Hind-III .So far, over 475 types of restrictions endonuclease enzymes have isolated and identified.

Exonuclease enzyme: The enzyme which cut single strand of DNA, digesting base pairs on 5' to 3' end or at single stranded nick of a DNA strand.

Reverse transcriptase enzyme: It was discovered by Temin and Baltimore from retroviruses. Reverse transcriptase directs complementary DNA strand formation on the templates of m-RNA (RNA directed DNA synthesis or reverse of transcription process). It helps in in vitro synthesis of DNA or gene using specific m-RNA obtained from the cell. New gene can be obtained through this technique within a short duration using DNA polymerase enzyme and nucleotides of DNA molecules in triphosphate  form (dATP, dGTP, dTTp, dCTP.

S-I nuclease enzyme: It degenerates the single stranded DNA or single strand of a double stranded DNA with cohesive ends. As a result of action of S-I nuclease, cohesive ends are converted into blunt ends.

DNA polymerase enzyme: It is used for producing copies of DNA through PCR technique or replication  of DNA under usual  condition (DNA directed DNA synthesis). It was first discovered by Kornberg.

RNA polymerase enzyme: It is meant for transcription of DNA molecules, i.e, DNA directed RNA synthesis or synthesis of RNA on DNA templates. All types of RNA (m-RNA, t-RNA and r-RNA) are synthesized by DNA templates using RNA polymerase.