Understanding Biotechnology

What is Biotechnology

Overview of Biotechnology

History of Biotechnology

Why do we do biotechnology?

Biotechnology for the environment

Biotechnology for food and agriculture

Genetic technologies aim to make a living thing perform a specific task. This could be to fight disease, produce more food, or simply to make a flower blue. Gene technology enables us to produce varieties of plants and animals with desirable characteristics, and usually in more precise and efficient ways than by using conventional breeding techniques. Gene technology also has the advantage of being fast compared to most conventional breeding strategies, an important commercial consideration where ‘speed to market’ of a new variety is critical.

This is because gene technology enables us to identify which genes are responsible for particular characteristics, and then transfer those genes into a different living thing. Moreover, it is possible to transfer genes between species, something that occurs only rarely in nature. This process requires considerable caution and strict controls, because it may alter a species, and this could have unforeseen consequences in ecosystems that are not adapted to the new version. However, the advantage of transferring genes between species is that, compared to traditional breeding, scientists can select from a larger number of genes for desired characteristics.

Genes, DNA and chromosomes

Every living thing (apart from some viruses) contains DNA, which has the structure of a long twisted ladder - a double helix.   The rungs of this ultra-microscopic ladder are composed of molecules called ‘bases’. The sequence of these bases along the ladder spell out biological information. Hence, the order of bases in DNA determines what a gene produces or what it does.

The instructions for making an entire organism from a single fertilised egg cell are found in the genes. How an organism develops and functions is determined by its genes, in conjunction with environmental factors, such as nutrition, temperature, sunlight etc. Sperm cells and egg cells contain genes, but each sperm or egg contains only one copy of each gene, while other cells of an organism contain two copies.   When the egg is fertilised by the sperm, the genes recombine so that when genes are passed on from one generation to the next, each individual offspring inherits only some – not all – of each parent’s traits.

The number of genes in an organism varies greatly between different species. Most higher animals and plants have anywhere from ten thousand to about fifty thousand genes. Genes can be switched on or off at different times, and within different cells of the same organism. Also, many genes found in different species are remarkably similar – for example, the gene which codes for haemoglobin, the substance that enables our red blood cells to carry oxygen, is also present in many insects, worms and even some plants. However, each of these other species contains a slightly different version of haemoglobin – adapted for its particular needs – and hence a slightly different gene.

The discovery of genes and gene technology

In 1953, after some years working in collaboration with other scientists, Francis Crick and James Watson at Cambridge University announced the structure of  DNA. They realised that DNA’s sequence of bases, and its ability to copy itself, were the means by which genes both stored and copied information. (It is copying, known as replication, that allows genes to be inherited.) The researchers subsequently won a Nobel Prize.

Crick and Watson's discovery started a flurry of research. Scientists began to sequence the genetic code, showed how genes work, and revealed that all living things use the same essential DNA code. This underlined the unity of life, and it became clear that because genes are chemically the same and are read in virtually the same way in all species, genes of different individuals and organisms were potentially interchangeable. In nature, however, such gene exchanges across species are probably very rare, apart from between microbes.

Late in 1973, Dr Stanley Cohen of Stanford University and Dr Herbert Boyer of the University of California performed the first ‘gene cloning’ experiment. They used enzymes to cut two small circular pieces of DNA (plasmids) from bacteria, each containing a different antibiotic resistance marker and then joined them together to make a new plasmid. The new plasmid was then taken up by bacteria, which were thus made resistant to both antibiotics. Cohen later showed that inserted DNA could be ‘read’ by bacteria. If it contained the right code, it could enable the microbes to make proteins normally found only in other organisms..

Techniques of modern gene technology

Polymerase chain reaction (PCR) produces large amounts of a specific DNA fragment, providing the supply of DNA for insertion into another organism. An original piece of DNA is used as a template to make many copies. DNA polymerase is the enzyme responsible for making the copies of DNA, and the technique involves a chain reaction to produce a large amount of the copied DNA sequence.

Gel electrophoresis is a technique used to separate large biological molecules, including proteins or fragments of DNA. It helps scientists identify genes, or proteins, based on their size. The molecules move through an electric field in a gel, much like dessert jelly, at different speeds according to their size. Smaller molecules will move faster than large ones. This allows DNA segments of different sizes to be separated from each other. This technique is also used to produce the DNA 'fingerprints' that are often used in forensic science.

Blotting is a technique for isolating and identifying individual DNA molecules. Once DNA molecules have been separated by gel electrophoresis, a special absorbent material is placed on top of the gel where it picks up DNA molecules in the same way as blotting paper soaks up ink. Once the DNA molecules are on the blot, it is possible to probe them using labelled DNA to identify a specific gene or sub-set of DNA molecules.

Restriction enzymes and ligases are naturally-occurring enzymes used to cut and join pieces of DNA respectively. There is a whole family of restriction enzymes, which can be thought of as ‘DNA scissors’.  Each one cuts DNA at a specific, known place. DNA ligase is used to rejoin the DNA after cutting. DNA ligase can be thought of as ‘DNA glue’. By cutting and rejoining the DNA, a specific gene can be transferred into an existing DNA sequence.

Gene insertion involves the insertion of new genes into the cell's existing genetic material. Different methods are used to transfer genes into different living things.

In animals, the desired gene can be inserted by injecting the gene into a single-celled embryo. This embryo is then allowed to develop into an adult animal. This technique is called microinjection.

In plants, the gene of interest can be coated onto tiny metal particles which are then shot into the cell using a special gun. A second method uses bacteria, usually one from the Agrobacterium family as they have a natural ability to infect plant cells and incorporate the bacterial DNA into the plant cell. Scientists can add the desired gene to the DNA of the bacteria, which then enter the cells of the plant, transporting the gene in the process. The gene integrates into the DNA of the plant cell. This added or foreign gene is called a transgene.

With both techniques, the place where the transgene inserts and the number of insertion events are impossible to predict. The unpredictable nature of the transgene’s insertion can be a cause for concern.   Although an inserted gene may successfully function, its random insertion may have disrupted an existing complex of genes. Insertion, and the methods used to achieve it, can delete sections of existing DNA, or cause the addition of superfluous DNA. Thus effects on the plant other than that intended by the addition of the transgene may occur. These effects are called pleiotropic effects.

Plants have the interesting ability - under the right conditions - to develop from a single cell taken from an adult plant. Growing plants in this way is called regeneration and requires techniques known as tissue culture. Plant cells containing an added transgene that is stable and functioning are grown using tissue culture until they develop into a whole plant.   This plant will then produce seed containing the added gene, and the seeds can be used just like conventional seeds, to produce more transgenic plants.

For both animals and plants, the chance of new DNA becoming permanently fixed into the organism’s existing DNA is relatively low. For this reason, scientists expose many cells to the gene and then select those that have successfully taken up the new gene. Knowing which cells contain the inserted gene is made easier by the use of ‘markers’, explained below.

Marker genes therefore enable researchers to select among cells for the ones which have successfully received the new gene. Commonly used marker genes are those which give the cell the ability to withstand treatment with a chemical, such as an antibiotic or a herbicide. Scientists will treat all the experimental cells with the antibiotic or herbicide; only those that have received the gene for resistance will survive. Other marker genes may make the cell turn a particular colour or glow when exposed to ultra-violet light.

There have been serious concerns about the use of antibiotic resistance genes or herbicide resistance genes as markers, because of the risk of such genes spreading. (If disease-causing bacteria acquire these genes, then the relevant antibiotic will not kill them. The same applies to plant weeds acquiring herbicide tolerance.) Other marker genes include genes which enable a cell to use specific food sources that it would not normally be able to digest, or that allow cells to survive in the absence of particular growth additives.

Marker genes are tools that are designed for use only in the research stages of development of a genetically modified organism.  New techniques are also being used which can ensure markers are removed once their job is complete.