Originally created for DNA Interactive ( http://www.dnai.org ) TRANSCRIPT: A common technique in genetic engineering is to insert a new gene into a loop of bacterial DNA called a plasmid. The molecular tool used to cut DNA is a restriction enzyme such as EcoRI. The enzyme has a precise shape that allows it to run along the groove of the double helix, scanning for the base letter sequence G A A T T C EcoRI then cuts the plasmid at this specific point... ...allowing a new piece of DNA to be inserted. When it cuts, EcoRI leaves a sticky end, which helps the new gene to attach. The joins are THEN stitched together by another enzyme called DNA ligase. The genetically engineered bacteria is then grown in a culture medium. Very quickly, large numbers of the bacteria can be produced, each with a copy of the inserted gene. The bacteria duly manufacture whatever protein the gene codes for, and so the desired product is produced.