Molecule of the Month: Restriction Enzymes
Bacterial enzymes that cut DNA are useful tools for genetic engineering
Bacteria Fight Back
Molecular Scissors
Sticky Ends
An interesting property of restriction enzymes simplifies this molecular cutting and pasting. Restriction enzymes typically recognize a symmetrical sequence of DNA, such as the site of EcoRI shown in the figure. Notice that the top strand is the same as the bottom strand, read backwards. When the enzyme cuts the strand between G and A, it leaves overhanging chains. These are termed "sticky ends" because the base pairs formed between the two overhanging portions will glue the two pieces together, even though the backbone is cut. Sticky ends are an essential part of genetic engineering, allowing researchers to cut out little pieces of DNA and place them in specific places, where the sticky ends match.
Exploring the Structure
In both illustrations, the protein is shown with a simple backbone representation and one DNA strand is colored green. These illustrations were created with RasMol. You can create similar illustrations by clicking on the PDB accession codes above and picking one of the options for 3D viewing.
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August 2000, David Goodsell
http://doi.org/10.2210/rcsb_pdb/mom_2000_8