More food, cleaner food – gene technology and plants

Key text

Producing better crops

Crop plants and livestock were bred for desired qualities long before people knew anything about the science of genetics. Early plant and animal breeders selected good varieties and strains without really understanding the underlying genetics. However, now that we do have that understanding, traditional breeding methods have been refined and accelerated.

New varieties of plants are always needed. For example, diseases are continually arising in new forms which can attack previously resistant crops. Plant breeders need to be one step ahead of the pathogens and prepare new resistant varieties for release.

Gene technology provides a new tool

Traditional methods of selective breeding have been provided with a new tool – gene technology. We now have the potential to take a gene from one organism and move it into another. A number of different techniques have been developed that enable us to do this (Box 1: Adding a gene to an organism).

Gene technology not only gives us the potential to select the exact characteristics we want in an organism, but it also enables us to cross species barriers. For example, we can take an insecticide-producing gene from a bacterium and insert it into a plant, making the plant resistant to insect attack. This new-found ability to cross species barriers is what makes gene technology such a powerful tool.

Uses of gene technology

Producing enough food for the world's population without using up all the available land is an enormous challenge. One solution is to develop crops that yield more with fewer inputs; that are more resistant to diseases; that spoil less during storage and transport; that contain more useful nutrients; and that can grow in agricultural land that has been degraded. Gene technology gives us the potential to do this (Box 2: Some examples of Australian gene technology research).

Potential benefits; potential risks

Gene technology promises increased yields and reduced dependence on pesticides. However, as well as potential benefits, there are also potential risks. For example, if an insecticide-producing gene inserted into a crop plant accidentally 'escaped' into a wild relative of the crop, then the wild relative might become a problem weed.

Government safeguards

So, as with all new technologies, we must ensure that we proceed carefully (Box 3: Concerns about gene technology). Before genetically modified organisms are released into the environment, there is usually a prolonged period in which they are kept within a contained laboratory. Initial testing in a more open environment is then closely monitored and restricted. In Australia, both lab-based testing and field trials are overseen by the Genetic Manipulation Advisory Committee.

There are other bodies controlling the use of genetically modified organisms, including the Australia New Zealand Food Authority (ANZFA) and the National Registration Authority (NRA).

• Genetically modified organisms that end up as human food come under the umbrella of ANZFA. It develops and maintains food standards for Australia and New Zealand, in close consultation with State and Territory governments.

• NRA regulates agricultural and veterinary chemicals (eg, herbicides and pesticides). It is responsible for some genetically modified organisms such as pesticide-resistant plants.

Box 1. Adding a gene to an organism

Enzymes that cut and splice DNA are important tools for a genetic engineer

There are two basic techniques in manipulating DNA: cutting and splicing (ligating). Enzymes are used in both techniques. Restriction enzymes make breaks in the DNA, at specific sites. These enzymes are found in bacterial cells where they break down the DNA of invading viruses; scientists use restriction enzymes to cut DNA into manageable fragments. Another enzyme present in cells, DNA ligase, joins fragments of DNA together and can join DNA fragments from different organisms as easily as DNA fragments from the same organism. If DNA fragments from two different sources are mixed in a test tube with DNA ligase, sometimes the re-joining will put together the DNA from the two sources. DNA molecules composed of sequences derived from different sources are described as recombinant.

How scientists add a gene to an organism

Identifying a gene. To identify the gene for a particular characteristic from the huge amount of DNA within an organism is a daunting task. Before you begin, you need to know something about the gene; for example what protein it contains instructions to make or its base sequence.

Initially, scientists used information about the protein, such as its amino acid sequence, to eventually isolate the DNA molecule that contained the instructions for that protein. More recently, scientists have determined the entire sequence of bases that make up the genome of single-celled organisms. Projects to sequence the genomes of more complex organisms are well advanced. These projects include those aimed at sequencing the human genome and the genome of a small plant called Arabidopsis, a relative of commercially important plants such as oil-seed rape.

Proteins with similar functions often have similar structures, and the genes coding for these proteins will have a related base sequence. So, as more and more genes are identified, from more and more organisms, the task of identifying a new gene for a particular characteristic becomes easier.

Cloning DNA using bacteria. Scientists use a restriction enzyme to cut all the DNA of a donor organism into manageable fragments of a few thousand bases in length. They then splice each fragment into a bacterial plasmid, a small circular DNA molecule, to create a recombinant plasmid. Scientists reintroduce each recombinant plasmid into a separate bacterium, creating a bacterial 'library' of the donor DNA. To clone the DNA the bacteria are spread thinly on a nutrient agar plate so that each bacterium is well separated from the others. Each bacterium grows into a colony of millions of cells, each of which contains an identical recombinant plasmid with its DNA fragment from the donor organism. Since there are millions of cells, there are now millions of copies of each DNA fragment.

Finding the fragment that you want. Fragments are recognised by their sequence of bases. A gene probe is like a template that will recognise only the bacterial colony containing the DNA of the matching fragment. Once the desired colony is identified, the number can be increased (cloned) to produce more copies of the DNA fragment.

Getting DNA into the cell. Getting the cloned and purified fragment of DNA into a living cell is the next step. This step is more difficult in plants than animals, because plant cells have a cell wall in addition to a cell membrane. The following methods are those most commonly used to introduce DNA into a plant cell:

• Transporting DNA into a cell via a bacterium. The bacterium Agrobacterium tumefaciens infects many plants, causing tumours to form. The tumour-inducing DNA resides in a plasmid of the bacterium. When the bacterium infects a plant, part of this plasmid is transferred to the plant cell nucleus. Scientists have capitalised on this ability and now use Agrobacterium as a vehicle for introducing new DNA into plant cells. They ligate the DNA of a desirable gene into the bacterium's plasmid, and the new DNA is delivered into the nucleus of the plant cell. The transformed plant cell doesn't produce a tumour because scientists removed the tumour-inducing genes from the plasmid.

  The first version of Agrobacterium tumefaciens that did not initiate tumours was made in 1983 and has proved very successful. Using Agrobacterium to deliver a desired gene to a plant is now the most widely used method of gene delivery in plant genetic engineering.

• Removing the barrier of the plant cell wall. Not all plants are natural hosts of Agrobacterium tumefaciens. For example, wheat, rice and corn cannot be readily infected. So, for these plants, scientists remove the plant cell wall, producing a 'naked' plant cell. Without the barrier of the cell wall, DNA can more easily be delivered into the cell. One method used to introduce DNA into a 'naked' plant cell is to inject cloned DNA fragments using a very fine needle. Another is to produce pores in the cell membrane using short bursts of electric current. The DNA molecules can move through the pores which later mend.

  Removing the cell wall makes the plant cell fragile, so the success rate of delivering DNA into these 'naked' cells is low.

• Shooting the DNA through the cell wall using a 'gun'. The DNA gun (or particle gun) is the most recent technique used to modify plants. This gun shoots the DNA in through the cell wall, so the problems with naked cells do not arise. It is crucial that scientists fire the DNA-coated bullets – pieces of metal about 2 micrometres across – with just the right amount of force. If there is too much force, the cells will be destroyed by the blast. If there is too little, the bullet will not pass through the thick wall and into the cell. The holes in the cell wall and membrane mend quickly and the bullets, although they remain in the cell, appear to do no lasting damage. The DNA diffuses away from the bullet and, with luck, is incorporated into the DNA of the plant. CSIRO scientists have recently transformed wheat using this method.

Low rate of success

With any one of these three methods, however, the chances are still very small of getting the DNA to be accepted within one of the cell's chromosomes where it can function as a gene. To ensure that at least one cell receives the DNA at an acceptable spot on its chromosomes, scientists expose tens of thousands of plant cells to cloned DNA fragments. Easily identified genes, called marker genes, are sent in as part of the cloned DNA so that scientists can tell whether the inserted DNA has been accepted by the plant cell. A successfully transformed cell is then carefully nurtured into a fully developed plant. If this plant produces seed, some of the resulting seedlings will contain the transformed gene.

Related sites

• CSIRO Plant Industry, Australia
  • Tissue culture for gene transfer
  • Transforming genes into a bacterial ‘syringe’
  • Molecular scissors slice DNA to isolate genes
  • Understanding the ABC of DNA technology

• Plant transformation (Partnership for Plant Genomics Education, University of California, Davis, USA)

• Transforming plants – basic genetic engineering techniques (Access Excellence, USA)

Box 2. Some examples of Australian gene technology research

Insect-resistant cotton. In Australia, Heliothis caterpillars can strip cotton plants of their leaves and nibble their flower buds. The bud develops into the cotton fruit containing the seeds on which the cotton fibres grow, so loss of buds means less cotton is produced. The usual way to control this pest was to spray the plants with chemical pesticides, but now over 90 per cent of Australia’s cotton crop is genetically modified to resist this insect pest. The GM cotton plant produces a protein that is poisonous to the caterpillar, but harmless to other insects so preventing any serious damage to the developing flower buds. The information for making the protein comes from an additional synthetic gene, derived from a bacterium that has been added to the plant. GM cotton plants require far less insecticide than standard varieties of cotton. Pesticide use has been reduced by up to 80 per cent where the GM cotton is grown.

• GM cotton (transcript of ABC radio's The Science Show, 18 May 2002)

Virus-resistant clover

White clover provides protein for grazing animals, nitrogen for cropping, and helps improve soil structure and stability. Alfalfa Mosaic Virus (AMV) is a plant disease that reduces the productivity and persistence of the clover, costing dairy farmers in excess of $30 million per year.

Scientists from CSIRO and the Victorian Department of Primary Industries have developed clover with in-built resistance to AMV, providing the only control method for the virus so far. Researchers have also added natural resistance to Clover Yellow Vein Virus – the cause of another serious disease in white clover – to the AMV-resistant genetically modified clover.

Researchers are investigating the potential ecological impact of genetically modified white clover on natural and agricultural ecosystems.

Molecular Plant Breeding Cooperative Research Centre, Adelaide

The CRC aims to develop better varieties of wheat, barley, pasture grasses and clover using the technologies of molecular markers and genetic engineering. Molecular markers are the genetic signposts that flag the presence of genes controlling particular traits. For example, by identifying a gene that controls a plant's ability to tolerate salt, they could develop new crop lines that could grow in areas affected by salinity.

Plant Technology Centre, La Trobe University, Bundoora

At the Plant Biotechnology Centre, some research looks at traits that aren't associated with productivity. By genetically manipulating ryegrass – the variety of grass sown in lawns and pastures – researchers have been able to switch off the genes that produce the allergy-causing proteins in pollen.

• GM grass begins trials (transcript of ABC radio's Innovations, 14 September 2003.

Collaborative efforts

The Food Futures National Research Flagship draws together expertise from five CSIRO divisions and Food Science Australia (a joint venture of CSIRO and the Victorian Government).

Flagship researchers have developed plants that produce DHA (docosahexaenoic acid), a healthy omega-3 oil vital for human health. DHA is normally only available from fish sources which are declining worldwide. The breakthrough is an important first step towards improving human nutrition, reducing pressure on declining fish stocks and providing Australian grain growers with new high-value crops.

Scientists from the Grains Research and Development Corporation and CSIRO’s Plant Industry, Entomology and Molecular and Health Technologies are exploring the potential of plants to make compounds for a variety of industrial uses. More plastics, paints and even nylons could be made from chemicals produced in plants, an environmentally friendly replacement for non-renewable and increasingly costly petrochemicals currently used for the job.

The Victorian AgriBiosciences Centre, located at the La Trobe University Research and Development Park, was opened in January 2006. The consortium consists of the Department of Primary Industries, La Trobe University, the Molecular Plant Breeding CRC, Florigene Ltd, Monash and RMIT Universities. Research includes:

• helping plants survive drought and cold;
• boosting their salt tolerance;
• controlling when crops flower;
• enhancing crop yields;
• reducing crop losses to pest and diseases; and
• improving quality.

The Australian Centre for Plant Functional Genomics is working to improve the resistance of wheat and barley to hostile environmental conditions, using functional genomics technologies.

Scientists at the Centre focus on stresses that impact agriculture in Australia, including drought, salinity, high or low temperatures and mineral deficiencies or toxicities. These stresses are a major cause of cereal crop yield and quality loss throughout the world.

The private sector

The company Florigene Ltd has produced mauve ‘Moon’ carnations by inserting a petunia gene into the carnation plant. The company's researchers have also produced a strain of carnations which stay fresh for longer when picked. The eventual browning and decay of picked flowers, even when their stems are in water, is caused by the production of the gas, ethylene. Using antisense genes, the researchers have 'switched off' the gene that codes for the production of ethylene in the plant. The genetically modified carnation retains its freshness and colour long after ordinary carnations have shrivelled and turned brown.

While the potential benefits of gene technology are immense (eg, higher yields, resistance to pests and diseases, adaptation to particular environments, and increased convenience in harvesting and storage), many people have a number of concerns about genetically modified organisms.

Pesticide resistance

It is now possible to genetically engineer plants that produce their own pesticide. This exposes pests to the pesticide every day rather than as burst of pesticide application by the grower. If the pesticide-producing capability is introduced into a number of different plant species, it could accelerate the development of pesticide resistance among pests. (To reduce this concern the US Environmental Protection Agency has restricted the sales of pesticide-producing corn to states that do not grow pesticide-producing cotton.)

Increased use of herbicides

When farmers spray a herbicide to remove weeds growing among crops, the sprayed chemical often damages the crop plants. If the crop is engineered to be resistant to the chemical, the weeds will be killed but the crop plants will remain undamaged.

At first glance, this seems like a good thing. But it is likely to lead to greater use of the particular herbicide, which would have two negative effects:

• The crop is likely to contain greater herbicide residues; and
  
• the increased spraying will contaminate the rest of the environment.

Of course, not all herbicides are dangerous, but it seems safer to minimise rather than encourage their use.

Herbicide-resistant weeds

Genetic engineers are producing crops that are herbicide-resistant and pesticide-resistant. If the genes for these characteristics were to end up in a weed species, the weed would thrive and be difficult to control. (Field trials in Denmark of a genetically engineered, herbicide-resistant rape showed that the gene for herbicide resistance had jumped into a closely related plant.)

To label or not to label

One of the main points of controversy surrounding the release of genetically modified organisms is the question of labelling food products. Supporters of labelling point to potential problems for people with food intolerances. An investigation carried out in the mid-1990s found that seven out of nine people allergic to brazil nuts were also allergic to soya beans that had been genetically modified to contain a protein usually found in the nuts. These people showed no reaction to unmodified soya beans, so the protein taken from the brazil nuts must have been responsible for their allergic reaction. Because serious food reactions can kill, people need to know when genetically modified products might cause allergic reactions.

Supporters of labelling also point to the principle of the consumer's right to know what is in their food. Opponents point out that we don't know exactly what is in our food at the moment anyway. Many plants contain natural toxins to protect them against insect attack. These toxins are not good for us, and yet when we eat a parsnip we are not told the concentration of the potentially carcinogenic chemical that occurs naturally.

Concerns about marker genes

More serious worries stem from the use of marker genes. These are genes that are inserted into the genetically modified organism along with the desired gene. The presence of marker genes, which are easy to spot, allows researchers to recognise organisms that contain the desired gene. The problem arises with those marker genes that give antibiotic resistance to the organism.

Some people believe it is risky to allow genetically modified plants with marker genes for antibiotic resistance into the environment. For example, the British government objected to a proposal to import genetically modified corn from the United States into Europe because the plants contained a marker gene for resistance to the commonly used antibiotic, ampicillin. The government feared that the gene for antibiotic resistance could spread to bacteria that inhabit the human gut. In turn, these could pass the gene on to more dangerous bacteria. Or the marker gene could move from the plant into soil bacteria and then into disease-causing bacteria.

After much debate, in late 1996 the European Commission decided to allow the corn to be sold in Europe.

The role of big business

It is expensive to develop the potential that gene technology offers and it requires a long-term financial commitment to research. While large and well-funded corporations are able to provide this amount of money, there is some concern that the results of this research will not be readily accessible to small companies or developing countries. Some people are also concerned about placing responsibility for the world's food supply into the hands of a few large companies.

Tampering with nature

Critics of gene technology suspect that we still know too little about the systems that we are tampering with. Could an inserted gene have effects that we are unaware of? Could it upset the balance of existing genes, causing the plant to produce greater quantities of natural toxins, or to change its nutritional content?

Most researchers argue that there is no evidence of such unexpected changes. They point out that gene technology is much less likely to have unwanted effects on a plant than traditional selective breeding methods. These traditional methods, which have been carried out for thousands of years, involve the movement of thousands of genes from one organism to another. Modern gene technology, on the other hand, moves only a few targeted genes.

Safeguards

Food Standards Australia New Zealand (formerly ANZFA) develops food standards for composition, labelling and contaminants that apply to all foods produced or imported for sale in Australia and New Zealand. Food standards are developed with advice from other government agencies, stakeholders and food regulatory policies, and apply to the entire food supply chain from ‘the gate to the plate’.

The Office of the Gene Technology Regulator (OGTR) is the government agency responsible for gene technology regulation in Australia. The OGTR provides administrative support to the Gene Technology Regulator, who is responsible for enforcing the Gene Technology Act 2000. According to the OGTR web site, the Act is ‘a national scheme for the regulation of genetically modified organisms in Australia, in order to protect the health and safety of Australians and the Australian environment by identifying risks posed by or as a result of gene technology, and to manage those risks by regulating certain dealings with genetically modified organisms’.

‘Dealings’ include research, production, manufacture, import, storage, transport and disposal of genetically modified organisms (GMOs). To release a GMO into the environment, the Regulator prepares a risk assessment and risk management plan by consulting scientific experts, stakeholders and the public. The Regulator then decides whether or not to issue a licence to allow the release of a GMO.

Related sites

• The great GT debate (CSIRO Australia)

• Gene technology and food (National Science and Industry Forum report – Australian Academy of Science)

• Genetically modified plants for food use and human health – an update (The Royal Society, UK)

• Australian Broadcasting Corporation
  • GM or not GM (transcript of The Science Show, 20 July 2002)
  • The public perception of risk in genetic modification (transcript of Ockham's Razor, 27 January 2002)

• Assessing the safety of new foods and technologies (Food Standards Australia New Zealand)

• About the OGTR (Australian Government Department of Health and Aging)

Activities

• Biotechnology Australia
  • Extracting DNA in your kitchen – describes how to extract DNA from an onion.
  • Worksheets – provides a variety of activities (PDF files) relating to the use of biotechnology in food and agriculture production.

• InnovatED (IP Australia)
  • New plants from old: Lesson 1 – students learn the basics of genetics and plant breeding while gaining an understanding of the rationale behind this scientific practice.
  • New plants from old: Lesson 2 – students explore various Australian native plant varieties and investigate plant breeding and plant breeder's rights.
  • New plants from old: Lesson 3 – students create a labeled diagram of their new plant breed.

• Australian Academy of Science
  • Interviews with Australian scientists – supplies an interview with plant scientist Dr Liz Dennis, teachers notes and student activities.

• The Helix (CSIRO, Australia)
  • GM crops: The food of the future? – students explore the different view-points related to genetically modified (GM) crops.

• Careers in Science, Australia
  • Biotechnology – an introductory lesson to the study of the structure and manipulation of DNA – students study DNA to supply knowledge useful in their daily life and potential scientific careers.

• Iowa State University (USA)
  • Student exercise on polymerase chain reaction (PCR)

• Rural Source (New Zealand)
  • Genetically modified food (GMF) – provides a range of information on issues surrounding genetic engineering of food, along with classroom discussion topics and activity ideas.

• Public Broadcasting Service (USA)
  • Genetically-modified foods – students list both pros and cons of genetic engineering and use that information to form a personal opinion.

• National Center for Case Study Teaching in Science (University at Buffalo, USA)
  • All that glitters may not be gold: A troublesome case of transgenic rice – students explore social and biological issues surrounding vitamin A deficiency and how 'Golden rice' might address the problem. Case teaching notes are available.
  • Frankenfoods? The debate over genetically modified crops – students examine the scientific and ethical issues of agricultural biotechnology. Case teaching notes are available.
  • Torn at the genes: One family's debate over genetically altered plants – students discuss the controversial issue of genetic engineering in crops. Case teaching notes are available.

Further reading

• The future of GM crops and foods in Australia
• Genetically modified crops in Australia and abroad
• The long road ahead for GM foods in Australia
• Is Australia ready for GM foods?

• The reality in the field

• The strategy of coexistence

Useful sites

An introduction to gene technology – techniques, uses, concerns and regulations. There is a 'News' section with updates.
http://genetech.csiro.au/

Genetic engineering (University of Adelaide, Australia)

This site covers the basics of plant genetic engineering, and gives some examples of the use of genetic engineering in plant pest control.
http://www.adelaide.edu.au/agcareers/Content/TeacherResources/PestControl/Genetic.htm

Biotechnology fact sheets (Biotechnology Australia, Commonwealth Government)

A broad range of information sheets about biotechnology in Australia (eg, 'Biotechnology and food' and 'Gene technology techniques').
http://www.biotechnology.gov.au/index.cfm?event=object.showContent&objectID=F6C33ACE-BCD6-81AC-1FD796E193C1D74E

Global responses to GM food technology: Implications for Australia (Rural Industries Research and Development Corporation, Australia)

Gives the Australian perspective on the global market place for GM food and products.
http://www.rirdc.gov.au/reports/GLC/05-016.pdf

Australian Government Department of Agriculture, Forestry and Fisheries

• What's in the pipeline? Genetically modified crops under development in Australia
  Identifies a selection of GM crops under development in Australia and discusses significant barriers and bottlenecks to commercialisation.
  http://www.affashop.gov.au/PdfFiles/what_s_in_the_pipeline_-_full_report__2_.pdf

• Genetically modified crops in Australia: The next generation
  Highlights the key findings of the study.
  http://www.affa.gov.au/content/publications.cfm?ObjectID=17D7E073-2B1C-4B6C-89276D6DD41DA84D

Genetic engineering and agriculture: Australian farming at the crossroads (Parliament of Australia)

An excellent overview of the situation in Australia regarding genetically modified organisms. This November 1999 paper covers areas such as farmers' attitudes, labelling and environmental impacts.
http://www.aph.gov.au/library/pubs/rp/1999-2000/2000rp08.htm

Designer seeds (Beyond Discovery, National Academy of Sciences, USA)

Uses genetically engineered crops as an example to show how basic research in science can lead to practical results. (A PDF file of the complete article is available.)
http://www.beyonddiscovery.org/content/view.article.asp?a=167

Australian Broadcasting Corporation

• The DNA files – designing the garden: Food in the age of biotechnology (The Science Show, 21 June 2008)
  A discussion of developments in food biotechnology.
  http://www.abc.net.au/rn/scienceshow/stories/2008/2277054.htm

• GM food and the eye of the beholder (Ockham's Razor, 28 September 2003)
  Looks at the history of the genetic modification of plants and why GM seed could benefit developing countries.
  http://www.abc.net.au/rn/science/ockham/stories/s953676.htm

Glossary

antisense gene. A gene which produces RNA molecules complementary to the normal messenger RNA of the target gene. Antisense genes prevent expression of the target gene and are used to selectively turn off production of certain proteins.

bacterium (plural bacteria). A single-celled, microscopic organism without a distinct nucleus.

base (in DNA). Any one of four nitrogenous (nitrogen-containing) bases (adenine, thymine, guanine and cytosine). The sequence of the bases in DNA determines the sequence of amino acids in all proteins found in living things.

chromosome. A long DNA molecule that contains the genes of the organism. Chromosomes are visible in cells during cell division.

clone. A group of organisms, cells or DNA sequences derived from the same ancestor.

DNA (deoxyribonucleic acid). The nucleic acid forming the genetic material of all organisms with the exception of some viruses which have RNA. DNA is present in the nucleus and other organelles such as mitochondria and chloroplasts.

DNA fingerprinting. Identification of the DNA of different individuals based on variation that exists between them in the sequence of bases in the DNA.

enzyme. A protein that acts as a catalyst. Every chemical reaction in living organisms is facilitated by an enzyme.

gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.

gene probe. A specific sequence of single-stranded DNA or RNA, usually labelled with a radioactive atom. A probe is designed to bind to, and therefore single out, a particular segment of DNA to which it is complementary.

gene technology. The techniques used in the manipulation of DNA to alter the genetic make-up of organisms.

genetically modified organism. An organism with genetic material that has been altered using gene technology.

genetics. The study of heredity and variation in organisms. It can also refer to the genetic features of an organism.

genome. The total genetic material of an individual or species.

marker gene. An easily identified gene that is inserted into the organism, along with the desired gene. The presence of the marker gene tells researchers that the transformation was successful.

nutrient agar plate. A sterile, enclosed dish with a layer of a jelly-like substance containing complete food requirements for growth of bacteria, other small organisms or cells. If the bacteria are well-spaced when they are introduced to the plate, each bacterium will produce a colony of bacteria.

pathogen. An organism capable of causing a disease.

plasmid. A small, circular DNA molecule. Bacteria can have plasmids in addition to the DNA of the main chromosome. Foreign DNA can be added to plasmids. The modified plasmid then transports the DNA into a new cell.

protein. A large molecule composed of a linear sequence of amino acids. This linear sequence is a protein's primary structure. Short sequences within the protein molecule can interact to form regular folds (eg, alpha helix and beta pleated sheet) called the secondary structure. Further folding from interaction between sites in the secondary structure forms the tertiary structure of the protein.

Proteins are essential to the structure and function of cells. They account for more than 50 per cent of the dry weight of most cells, and are involved in most cell processes. Examples of proteins include enzymes, collagen in tendons and ligaments and some hormones. More information can be found at Protein structure and diversity (Molecular Biology Notebook, Rothamsted Research, UK).

restriction enzyme. Restriction enzyme is a shorthand way of saying restriction endonuclease. (Nuclease = an enzyme that cuts a nucleic acid; endo = cuts in the middle, not at the ends; restriction = cutting is restricted to specific sites.) Therefore it is an enzyme that cuts the DNA molecule at specific locations along its length. Each type of restriction enzyme recognises a particular base sequence of the DNA and cuts precisely at the same point each time. (For example, the restriction enzyme EcoR1 recognises the sequence GAATTC, and cuts between the G and its adjacent A. The complementary strand of DNA has the sequence CTTAAG, and here also the enzyme cuts between the A and the G.)

RNA (ribonucleic acid). A nucleic acid similar to DNA. There are a number of types of RNA, the major ones being messenger RNA, transfer RNA and ribosomal RNA. RNA can serve as a messenger between DNA and proteins, as a structural molecule, as an enzyme and as regulators of gene expression. In some viruses RNA is the genetic material. For more information see Introduction to RNA and its functions (University of Newfoundland, Canada).

species. Living things of the same kind that are potentially capable of breeding and producing fertile offspring. Theoretically, plants or animals of different species cannot interbreed. However, occasionally this does not hold true.

virus. A submicroscopic infectious agent consisting of a nucleic acid (DNA or RNA) molecule surrounded by a protein coat. Viruses cannot replicate outside a living cell. More information can be found at How viruses work (How Stuff Works, USA).