Fig. 3.1 shows a bacterial cell that contains a circular loop of DNA called a plasmid. Scientists use bacteria of this kind to manufacture human insulin, th...
Question 1 Report
Fig. 3.1 shows a bacterial cell that contains a circular loop of DNA called a plasmid. Scientists use bacteria of this kind to manufacture human insulin, the hormone that many people with diabetes need to inject each day. To make the bacteria produce this human protein, workers cut the gene for insulin from a human chromosome and join it into the plasmid before returning the plasmid to the bacterium. The bacteria then divide rapidly in large tanks, producing insulin that is identical to the natural human hormone. This method allows very large quantities of the hormone to be made cheaply and reliably for use by patients.
(a) State the name given to a circular piece of DNA found in a bacterium, as shown in Fig. 3.1. [1]
(b) Describe how the human insulin gene is transferred into the bacterium during genetic engineering. [4]
(c) Explain why the insulin produced by the genetically modified bacteria is suitable for treating human patients. [3]
(d) Suggest two reasons why bacteria are useful organisms for producing large amounts of insulin. [2]
Answer Details
This question tests genetic engineering, using bacteria and plasmids to manufacture human insulin.
(a) A circular piece of DNA found in a bacterium is called a plasmid. [1]
(b) How the insulin gene is transferred into the bacterium [4] (1 mark each): the insulin gene is cut out of the human chromosome using (restriction) enzymes [1]; the plasmid is cut open using the same enzyme so the cut ends match [1]; the insulin gene is joined into the plasmid (sealed by an enzyme) to form a recombinant plasmid [1]; and the plasmid is put back into the bacterium, which takes it up. [1]
(c) Why the insulin produced is suitable for patients [3]: the modified bacteria contain the human insulin gene [1], so they make insulin with exactly the same structure as natural human insulin [1]; the body therefore accepts it and it is not rejected, working just like the person's own hormone. [1]
(d) Two reasons bacteria are useful (1 mark each) [2]: they reproduce and divide very quickly, so their numbers build up rapidly; and they are easy and cheap to grow in large tanks, so large numbers give a large yield of insulin.
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