Restriction enzymes are short nucleotide
isolated from bacteria cells that protect them from virus.
When a viral DNA enters the bacterial cell, the
restriction enzyme is able to recognize a specific sequence
(restriction site) on the DNA molecule, which is usually 4-8 nucleotides long. The restriction enzyme will cut the viral DNA at
these sites and hence restrict the growth of the virus.
Several hundreds of these enzymes have been isolated
from various organisms and most are available commercially. These
enzymes are used to cut a segment of gene from a human DNA
Restriction enzymes can either produce
sticky ends or
blunt ends. Sticky ends are produced by cutting the DNA in a
staggered manner within the recognition site producing
single-stranded DNA ends. These ends have identical nucleotide
sequence and are sticky because they can hydrogen-bond to
complementary tails of other DNA fragments cut by the same restriction enzyme.
Sticky ends will tend to recombine to form a single strand of