 Also
called restriction endonucleases
 Proteins produced by bacteria as a defense
against “foreign” DNA

Serve as bacteria’s “immune system”
 Specific
sequences of DNA that certain
restriction enzymes recognize

Examples:

EcoRI cuts at DNA sequence GAATTC
CTTAAG
 The arrows point to the cut sites in the DNA
sequence
 Hydrogen bonds between the nitrogen
bases fall apart after the cuts are made
 Restriction sites leave “sticky ends”
because little tails are left making it easier
for the complementary ends to rejoin

More examples
 AluI
cuts at DNA base sequence AG CT
TC GA
 Do these cut ends leave sticky ends?
 NO!
 When the restriction enzymes cut the
two DNA strands directly across from
one another they produce “blunt
ends”.
 Because
all living things have DNA that
shares the same basic structure we can use
bacterial restriction enzymes to “cut” DNA in
any organism and insert desired genes
 Enzymes called ligases stick the new bonds
together creating a segment of DNA that
contains new genes.
 New DNA is called recombinant DNA
 Production
of insulin by bacteria cells to
create supplies of insulin for diabetics.
 Transgenic corn that has been inserted with a
gene that makes it more resistant to pests
 Many more!!

Assignment: Find two real life uses of restriction
enzymes in genetic engineering. Bring your
articles in and be prepared for a discussion on
Monday.