How to Make Insulin for Fun and Profit:
A Brief Introduction to
Recombinant DNA

Decades ago, molecular biologists discovered a class of bacterial enzymes that they called restriction endonucleases. Restriction endonucleases have an interesting property: they cut DNA, but only at specific sequences, and they cut it in such a way that one strand ends up longer than another. For example, the restriction endonuclease EcoR1 cuts DNA only where it finds GAATTC matched with CTTAAG. It cuts between G and A, as shown in figure 15. The staggered ends left behind by EcoR1 are called “sticky ends,” for reasons that will be clear in a moment. 

 

Figure 26. Scission of DNA by Restriction Endonuclease to Form Complementary Sticky Ends. The endonuclease cuts as shown by the dotted red line. The resultant strands have staggered ends which will bind to any other strand with ends cut by the same endonuclease.