To work with an individual gene, scientists searched for a technique to snip the gene free from the rest of the DNA sprawling around it. The discovery of restriction endonucleases – proteins that cut out regions of DNA – provided scientists with the "molecular scissors" they needed. (DNAi Location: Manipulation > Revolution > Pieces of the puzzle > Restriction enzymes)

This animation shows how a restriction enzyme (in blue) moves along a DNA molecule (in red) and breaks the sugar-phosphate bonds, leaving behind what are known as "sticky ends."

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