How is a useful gene transferred from one organism into bacteria to make a product such as insulin?
Genetic engineering as the transfer of a gene from one organism to another, the ordered stages using a bacterial plasmid and enzymes, and the production of human insulin by genetically modified bacteria as the key example.
An SQA National 5 Biology answer on genetic engineering, covering the transfer of a gene from one organism to another, the ordered stages using a bacterial plasmid and enzymes, and the production of human insulin by genetically modified bacteria as the key example.
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What this dot point is asking
The SQA wants you to define genetic engineering as moving a gene from one organism into another, describe the ordered stages that use a bacterial plasmid and enzymes, and use the production of human insulin by genetically modified bacteria as the worked example.
What genetic engineering is
Bacteria are the usual receiving organism because they carry plasmids, small rings of DNA that are easy to open up and add a gene to, and because they multiply very quickly.
The stages, in order
The same kind of enzyme that cuts the gene out of the donor also cuts the plasmid open, so the gene and the plasmid have matching ends and join together neatly.
Making human insulin
The headline example is insulin, the hormone that controls blood glucose. People with type 1 diabetes need insulin injections.
- The human insulin gene is identified and cut out of a human chromosome.
- It is inserted into a bacterial plasmid, which is returned to a bacterium.
- The bacteria are grown in large tanks. As they multiply, each cell reads the inserted gene and makes human insulin, which is then collected and purified.
Because the inserted gene is the real human gene, the insulin made is genuine human insulin, and because bacteria multiply so fast, it can be produced in huge amounts cheaply.
Examples in context
Example 1. Insulin before genetic engineering. Before the 1980s, insulin for diabetics was extracted from the pancreases of pigs and cattle. It was expensive and some patients reacted to the slightly different animal protein. Genetically engineered human insulin solved both problems: it is identical to human insulin and can be made in unlimited quantity by bacteria.
Example 2. Human growth hormone. The same method is used to make human growth hormone for children who do not make enough of their own. The growth hormone gene is inserted into bacteria, which are grown to manufacture the hormone, again avoiding the need to extract it from human tissue.
Try this
Q1. Name the small ring of bacterial DNA used to carry a gene in genetic engineering. [1 mark]
- Cue. A plasmid.
Q2. State what is used to cut the gene out and to cut the plasmid open. [1 mark]
- Cue. Enzymes.
Exam-style practice questions
Practice questions written in the style of SQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
SQA N5 style4 marksDescribe the main stages used to produce human insulin by genetic engineering.Show worked answer →
A 4-mark describe answer should put the stages in the correct order. Award one mark per correct step, up to four.
First, the gene that codes for human insulin is identified and cut out of a human chromosome using enzymes.
Second, a plasmid is removed from a bacterial cell and cut open using enzymes.
Third, the insulin gene is inserted into the open plasmid, and the plasmid is sealed, then put back into a bacterial cell.
Fourth, the modified bacteria are grown and multiplied in large numbers, and as they multiply they make human insulin, which is collected.
Markers reward the correct sequence: identify and cut out the gene, open the plasmid, insert the gene, and grow the bacteria to make the product.
SQA N5 style2 marksExplain why bacteria are useful for producing a human protein such as insulin.Show worked answer →
Two ideas are needed: that bacteria can be modified, and that they multiply fast.
Bacteria carry plasmids, small rings of DNA that can be cut open and have a human gene inserted, so a bacterium can be given the instructions to make a human protein.
Bacteria also reproduce very quickly, so a modified bacterium can be grown into vast numbers in a short time, each cell making the protein. This produces a large quantity of insulin cheaply.
Markers reward (1) the plasmid allowing a gene to be inserted and (2) the rapid multiplication giving a large yield.
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Sources & how we know this
- SQA National 5 Biology Course Specification — SQA (2019)