Inside all your cells, like the cells of all living organisms, is DNA. This DNA contains the instructions for a whole range of features that make up an organism. Each segment of DNA, that is each individual set of instructions within the DNA, is a called a gene. There are genes that determine eye colour, there’s a gene that determines whether you’ll have straight or curly hair, and there’s a gene that gives instructions to specific cells in the pancreas to produce insulin - a protein that helps control your blood glucose levels.
There’s a condition, known as diabetes where the body can’t control its blood glucose levels. There are different types of diabetes, but basically it’s a situation where the body either can’t produce or can’t correctly use insulin. The solution for many people in this situation is to take regular injections of insulin.
The problem is, where do you get spare insulin? A while back we used to use animal insulin, usually from cows or pigs. These days, using genetic engineering we can make human insulin. We take the gene, the genetic instructions, for human insulin, and insert that gene into bacteria cells, and allow the genetically modified bacteria cells to make to make the insulin for us.
Here’s how it works:
Bacteria cells have little circles of DNA in them called plasmids. We take out these plasmids and then use a restriction enzyme to open up them up. The plasmids now have what we call ‘sticky ends’.
Next we need the gene for the feature that we want, in this case the gene for human insulin from a human cell. We use the same restriction enzyme that we used with our plasmid to cut out the human insulin gene. It now also has sticky ends.
The human insulin genes are then mixed with the open plasmids, along with an enzyme called ligase. Ligase helps join the sticky ends of the human gene to the sticky ends of the plasmid.
Here you can see what’s known as a recombinant plasmid which is a combination of the original bacteria DNA and the human insulin gene.
The recombinant plasmids are then inserted into bacteria cells. Now, we’ve got recombinant bacteria.
The final step is to grow the bacteria in ideal conditions in a fermentation tank, allowing them to divide and replicate many times, all the while producing lots and lots of human insulin based on the genetic instructions they now have. This insulin can then be collected, purified and bottled, ready for use by humans.
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