(a) Restriction enzymes :

1. Restriction enzymes belong to the class of enzymes nucleases which breaks nucleic acids by cleaving their phosphodiester bonds.
2. Since Restriction endonucleases cut DNA at specific recognition site, they are used to cut the donor DNA to isolate the desired gene.
3. The desired gene has sticky ends which can be easily ligated to cloning vector cut by same restriction enzymes having complementary sticky ends to form recombinant DNA
4. An example is EcoR1 which is obtained from E.coli bacteria “R” strain which cuts DNA at specific palindromic Recognition site.
   5‘ GAATTC 3‘
   3‘ CTTAAG 5‘

(b) Plasmids :

1. Plasmids are autonomous, extrachromosomal circular double-stranded DNA of bacteria
2. Since they are small and self replicating,they are used as cloning vectors in genetic engineering.
3. Some plasmids have antibiotic resistance genes which can be used as marker genes to identify recombinant plasmids from non-recombinant ones.
4. The plasmids are cut and ligated with desired genes and transformed into a host cell for amplification to obtain the desired products.
5. An example of artificially modified plasmids is pBR322 ( constructed by Bolivar and Rodriguez) or pUC (constructed at university at California).