| Enzymes | Reaction and mechanism | cofactor | Condition of reaction | Applications in biotechnology | 
    | DNA Polymerase-I |   A 5\'3\' (forward) DNA-Dependent DNA polymerase activity, that  requires a 3\' primer site and a template strandA 3\'5\' (reverse) exonuclease activity that mediates  proofreadingA 5\'3\' (forward) exonuclease activity mediating nick  translation during DNA repair.A 5\'3\' (forward) RNA-Dependent DNA polymerase activity | Mg+2 |   1x NEBuffer2Incubate at 37°C | DNA Polemerase is mainly used in PCR (Polymerase Chain  Reaction) to add nucleotides in the growing chain using template  DNA. | 
    | Klenow fragment |   Klenow fragments are protiens that are formed by cleavage of  DNA polymerase I with protease subtillisin.It persist its polymerase and 3’  5’ exonuclease activity for  proofreadingIt loses 5\'  3\' exonuclease activity which was present in DNA  polymerase I | Mg+2 |   1x NEBuffer2Incubate at 25°C |   synthesis of double stranded DNA from single stranded  templateFor the digestion of 3\' protruding overhang of telomeraseAlso used in PCR for extensive amplification of DNA  template | 
    | Taq polymerase |   It is thermostable polymerase isolated from thermophillic  bacteria.It can give polymerase activity at higher temperatures and adds  nucleotide 5\'3\' during PCR while other DNA polymerase cannot  remain active at that temperature (95°C) | Mg+2 | 1x standard taq reation buffer pack. |   Most commonly used polymerase in PCR reactionsPrimer extensionDNA sequencing | 
    | Reverse transcriptase |   Used to generate compementary DNA (c-DNA) from the RNA  templateRNA-dependent DNA polymerase activity,Ribonuclease H, andDNA-dependent DNA polymerase activity. | dNTP, Mg+2 Mn+2 |   1X Reverse Transcriptase Reaction BufferIncubate at 42°C |   Used for the process reverse transcriptionUsed by retrovirusesUsed to form cDNA libraryUsed for the PCR | 
    | Primase |   It is a kind of polymerase and catalyse the synthesis of short  RNA segment called primers.It does not require the DNA or RNA template as primer for the  polymerase activity as it synthesise its own primer. This primer  then can be removed by exonuclease activity.It bind to the helicase and starts synthesising primer during  DNA replication. | NOXIN | --- |   It is used to synthesise primers.It can be used to start DNA replication without using any  primers. | 
    | RNA polymerase |   DNA dependant RNA polymerase used in the transcription  process.It initiates the transcription from the DNA primer.It has helicase activity so, it doesn\'t need helicase to unwind  the DNA.RNAP bind to the sigma factor first to open up its active site  and then binds to DNA primer for the transcription of unwound  DNA. | sigma factor |   1X RNA Polymerase Reaction BufferIncubate at 37°C |   RNA synthesis from E. coli promoterTranscription initiation studies. | 
    | DNA ligase |   It promotes the joining of DNA strands by the formation of  phosphodiester bond.Also repairs the single stranded breaks by joining them.  ATP is required for the ligase reaction, which proceeds in three  steps: | NAD+, ATP |   1X DNA Ligase Reaction BufferIncubate at 16°C |   Used for cDNA cloning for joining the DNA strandsUsed with restriction enxyme to insert DNA fragment into  plasmids. | 
    | Helicase |   Used in DNA replication for unwinding the double stranded  DNAThe required energy for this comes from the hydrolysis of  ATP. | --- |   1x standard reaction buffer |   To unwind the double stranded DNATO unwind the DNA-RNA hybridFor some specific kind of PCR reaction | 
    | Topoisomerase type I |   It controls and alters the topologic states of DNA during  transcription.It catalyzes the transient breaking and rejoining of a single  stranded DNA which leads to the rotation of the broken strand, thus  altering the topology of DNA. | --- |  |   For the changing of topological states it is usedNo important use in biotechnology | 
    | Topoisomerase type II |   It cuts both strands of the DNA helix simultaneously in order  to check DNA tangles and supercoils.They use the hydrolysis of ATP as a source of energyThis is commonly known as gyrase and used in DNA replication  for releasing the supercoiling of the DNA strand. | --- |  | For unwinding the DNA suoercoiling it is used. | 
    | Restriction enzymes |   These are enzymes used to cut the DNA or RNA strands from the  restriction sites that are present in the perticular strandEach DNA have perticular sequence to which these enzymes bind  and cut that nucleotides. These sequence containing sites are  called restriction sites. | S-Adenosyl methionine (AdoMet), hydrolyzed ATP, Mg2+  , | Typically standard restriction enzyme buffers which are  different for different enzymes. |   Insertion of genes into plasmid vectors in the process of gene  coding and protien purification.DNA fingerprintingTo digest DNA for the souther blot analysis.Gene sequencing |