The circles can be broken and new genetic material added to them. Plasmids augmented with new genetic material can move across microbial cell boundaries and place the new genetic material next to the bacterium's own genes. Often the bacteria will take up the gene and begin to produce the protein for which the gene codes. Where the new gene codes for insulin, for example, the bacterium will begin to produce insulin along with its other gene products. A large vat of bacteria engineered to produce insulin can then become a sort of pharmaceutical factory.
Viruses can also act as vectors in genetic engineering.
Viruses are infectious particles that contain genetic material to which a new gene can be added. The virus can carry the new gene into a recipient cell in the process of infecting that cell. The virus can also be disabled so that while it can carry a new gene into a cell, it cannot redirect the cell's genetic machines to make thousands of copies of itself. Microinjection Other methods do not rely on biological vectors like plasmids and viruses. One of these is called microinjection and involves simply injecting genetic material containing the new gene into the recipient cell.