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 EcoR1;
the enzyme has a precise shape that allows it to run along the groove of the
double helix, scanning, in the case of EcoR1, for the base letter sequence GAATTC.
The enzyme then cuts the plasmid at this specific point, allowing a new piece of DNA to be inserted.
When it cuts, EcoR1 leaves a sticky end; this helps the new gene to attach.
The joins are then stitched together by another enzyme called DNA ligase.
The genetically engineered bacteria is 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 made.