Genetic engineering

Stage 1: The desired gene can be removed from the DNA of the donor organism using enzymes called restriction endonucleases. These are enzymes which chop up DNA strands by cutting them at specific sites, so they can be used to remove very specific genes. Certain types of restriction endonucleases are particularly useful because they leave small regions of DNA sticking out at each end of the required gene. These are known as sticky ends, and make it much easier to attach the gene into another piece of DNA.

Sometimes the required gene is synthesised artificially. Using another specialised enzyme known as reverse transcriptasereverse transcriptase
Viral enzyme in retroviruses that transcribes viral RNA into a DNA strand that can be used to direct the production of new virus particles. , the DNA sequence of the gene can be built up from isolated pieces of mRNA which have already been transcribed from the required gene.

Stage 2: The second step is to prepare a vector molecule to carry the DNA into the host cell – often a bacterium. A bacteriabacteria
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus. l plasmidplasmid
A piece of genetic material in a cell. Normally a small, circular strand of DNA, which is independent of the main genetic material of the organism.  (a small circular strand of DNA often found in bacteria in addition to their main DNA) is often used as a vector. These replicate quickly and independently of the main bacterial genome, and can therefore amplify the number of copies of the gene.

Plasmids usually carry a marker genemarker gene
This is a gene added in the process of genetic engineering along with the gene for a desired characteristic. The marker gene usually codes for a feature such as fluorescence or the ability to synthesise a specific nutrient, which enables scientists to identify successfully engineered organisms when it is expressed.  which is used to demonstrate the cells which have been successfully engineered. In the early days, these marker genes often coded for characteristics such as resistance to a particular antibioticantibiotic
Medicine that is used to treat bacterial infections and works by killing or stopping the growth and reproduction of bacteria. These can be specific to a particular bacteria or act on groups of related bacteria. . However, there were many concerns about the use of antibiotic resistance as marker genes, including the risk of them crossing into pathogens. In response, scientists modified their techniques and now other characteristics, such as fluorescence or the ability to synthesise a specific nutrient are used to identify the genetically modifiedgenetically modified
This indicates that an animal or plant has had its genetic makeup altered in some way. This is often by combining the genes from different organisms to produce an organism with desirable characteristics. organisms. So, for example, bacteria can be grown in a medium with a particular nutrient missing to show which cells have been successfully engineered: only the genetically-engineered organisms will be able to synthesise the missing nutrient and so only they will grow.

The bacterial plasmid is opened up using restriction enzymerestriction enzyme
Enzymes produced by certain bacteria which cut DNA at specific sites. They are widely used in genetic engineering. s which leave sticky ends that correspond to those of the new gene.

Stage 3: The third step is to join the new gene into the bacteriabacteria
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus. l plasmidplasmid
A piece of genetic material in a cell. Normally a small, circular strand of DNA, which is independent of the main genetic material of the organism. . The sticky ends are lined up and the gene is attached or annealed – using enzymes called DNA ligaseDNA ligase
An enzyme which is involved in DNA replication by catalysing the formation of phosphodiester bonds. s which join the pieces of DNA together.

Stage 4: The final step is to incorporate the engineered DNA into the bacterium or other cell where it is required. This is known as transformation and is usually achieved by suddenly heating up the bacteriabacteria
Single-celled organism. Has a cell wall, cell membrane, cytoplasm. Its DNA is loosely-coiled in the cytoplasm and there is no distinct nucleus. which makes their cell membranemembrane
A thin, flexible sheet-like structure that acts as a lining or a boundary in an organism.  more permeable so plasmidplasmid
A piece of genetic material in a cell. Normally a small, circular strand of DNA, which is independent of the main genetic material of the organism. can move into the cells. Once the plasmid is inside the host bacterium it will be expressed and a new protein made.