Restriction enzymes • Also called restriction endonucleases • Proteins produced by bacteria as a defense against “foreign” DNA • Serve as bacteria’s “immune system”
Restriction sites • 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”.
Significance of Restriction enzymes • 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
Real life benefits • 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.