1. Restriction Enzymes

2. What Are Restriction Enzymes? Endonucleases produced by prokaryote organisms that are capable of cutting DNA at specific sequences Found naturally in bacteria, used as a defense mechanism against invading nucleic acids Exploited by molecular biologists to cut DNA to be studied or modified at will

3. How Restriction Enzymes Work RE’s recognize a specific base sequence in the DNA, depending on what enzyme you are using RE’s cut the DNA between the specific bases within or near that sequence, called the restriction site The result of the cut can either be “blunt” or “sticky” ends

4. Types of Restriction Enzymes Type I: cut 100 bases after the restriction site Type II: cut at the restriction site Type III: cut 20-30 bases after the restriction site The type of enzyme used depends on the desired outcome

5. Blunt Cuts Do not have an overhang Always compatible with other blunt ends for ligation purposes Some enzymes use this type of cut

6. Sticky Cuts Leave an overhang of bases Sequence of material to be ligated must be complementary to overhang Many enzymes use this type of cut

7. Where Do We Get Them? Commercially there are several hundred RE’s available Obtained from different species of bacteria Named for the bacteria they come from

8. Uses of Restriction Enzymes To cut DNA (obviously) For determination of length of DNA extracted For determination of presence of insert To allow DNA to be cut and pasted For preparation of molecular standards To make a chromosome map