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Interactives -- DNA

Genetic Engineering : Engineering a Plasmid

Most genetic engineering involves bacteria. The first step in genetic engineering is to remove the gene you are interested in from its host organism. Here, we are going to remove the lux gene from a type of marine bacterium. The gene makes a protein that causes the bacterium to glow. To remove the gene, we must cut it out of the bacterium's DNA.

We cannot cut DNA with scissors or any other mechanical tool. Instead we have to use substances from bacteria called restriction enzymes. Restriction enzymes cut apart DNA at specific locations that are determined by the DNA sequence. If we know the sequence of the gene we want to use, we can choose a restriction enzyme that cuts before or after the gene, but not inside it. The restriction enzyme snips out the gene. Often, two different restriction enzymes are needed; one will cut the DNA strand before the gene, and the second will cut the DNA after.

Some enzymes cut the DNA to produce DNA with short, single-stranded pieces at the ends; they are called sticky ends. Restriction enzymes that produce sticky ends are the most useful in genetic engineering.

This diagram shows where restriction enzymes are cutting the DNA. When the DNA is cut, the sequence of proteins is changed. By breaking the chain, scientists are preparing to "engineer" a new DNA molecule.


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