Genetic Engineering

What genetic engineering is

Genetic engineering is the deliberate alteration of an organism's genetic material, usually by transferring a gene from one organism into another so that the recipient organism produces a new characteristic or product. It is also called recombinant DNA technology, because it combines DNA from two different sources into one molecule.

The basic steps

1. Identify and isolate the desired gene from the source organism's DNA.
2. Cut out the gene using a restriction enzyme, which recognises and cuts DNA at a specific sequence.
3. Cut open a vector, usually a bacterial plasmid, using the same restriction enzyme, creating matching ends.
4. Insert the gene into the vector, and use an enzyme called DNA ligase to join, or splice, the pieces together, forming recombinant DNA.
5. Transfer the recombinant DNA into a host cell, such as a bacterium, which then expresses the new gene and produces the desired protein.

Examples and applications

Human insulin, once extracted from animal pancreases, is now mass-produced by inserting the human insulin gene into bacteria, which then manufacture insulin cheaply and in large quantities. Other applications include Bt crops, engineered with a gene from a soil bacterium to resist certain insect pests, and crops engineered for improved nutrient content, such as vitamin A enriched rice.

Because the inserted gene comes from a different species, an organism produced this way is called a genetically modified organism (GMO), and a genetically modified crop is often referred to simply as a GM crop.

Benefits and limitations

• Genetic engineering allows a single desired trait to be transferred precisely, without carrying over the many other genes that would come with traditional cross-breeding.
• Because host organisms such as bacteria can be grown quickly and cheaply in large fermenters, products such as insulin can be mass-produced at a lower cost and in far larger quantities than by extracting them from animals or plants.
• Crops engineered for a specific benefit, such as vitamin A enriched rice, can help address a specific nutrient deficiency in a population's diet.
• A new genetically modified organism must undergo biosafety assessment before release, and its long-term effect on the environment and on biodiversity continues to be monitored and studied.

How this is examined

SPM questions commonly ask you to arrange the steps of genetic engineering in the correct order, to state the function of a restriction enzyme or DNA ligase, or to name and describe an application of genetic engineering, such as the production of human insulin using bacteria.

Worked exam-style question

Question. A biotechnology company wants to produce human insulin using bacteria. (a) Name the technique used to transfer the human insulin gene into a bacterium.

(b) Describe, in the correct order, the main steps involved, starting from isolating the gene from human DNA. (c) Explain why a bacterium, rather than a human cell, is chosen as the host organism for large-scale insulin production.

(d) State one advantage of producing insulin this way compared with extracting it from animal pancreases.

Model answer. (a) The technique is genetic engineering (recombinant DNA technology). (b) The human insulin gene is first isolated and cut out using a restriction enzyme, which recognises and cuts DNA at a specific sequence.

A bacterial plasmid vector is cut open using the same restriction enzyme, producing matching cut ends. The gene is inserted into the plasmid and sealed in place using DNA ligase, forming recombinant DNA.

This recombinant plasmid is then inserted into a bacterium, which expresses the gene and produces human insulin. (c) Bacteria reproduce rapidly by binary fission and can be grown cheaply in large fermenters, so insulin can be mass-produced far more quickly and in much greater quantity than would be possible using human cells.

(d) Insulin produced this way is chemically identical to human insulin and can be manufactured in a continuous, large-scale supply, unlike the limited and more variable supply obtained from animal pancreases.

Practice question

Try this. A researcher inserts a herbicide-resistance gene from a soil bacterium into the cells of a crop plant. (a) Name the type of organism produced by this process.

(b) Suggest one advantage this modified crop would have for a farmer.

Exam tip

Key terms

These terms from Chapter 28 are central to describing genetic engineering accurately:

• Genetic engineering, the direct transfer of a gene from one organism into another using recombinant DNA technology.
• GMO, an organism whose genetic material has been altered by genetic engineering.
• Biotechnology, the use of living organisms, or their products, to make or modify something for a practical purpose.
• DNA, the molecule that carries the genetic instructions cut, joined and transferred during genetic engineering.
• Cloning, producing a genetically identical copy of an organism or a piece of DNA.

Source:SRC-DSKP-EN

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