 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.