True or false• The DNA in the nucleus of the cell and mRNA are of the same size.

• The DNA must unwind before transcription can take place.

• mRNA contains thymine.

• All codons in an mRNA correspond to a particular amino acid.

• The transfer RNA cooperates with the ribosome in the translation process.

• ‘AUGGAAGCGACGUGAAAA’The above mRNA sequence is responsible for coding for 6 amino acids.

• During translation, the ribosome moves along the mRNA.

• In controlling the genes, cells will control the amount of proteins they will produce.

Control of genes

• Gene expression is controlled by cells.

• This means that genes which are ‘switched off’ do not produce proteins. Such genes are not expressed.

• Different cells express certain genes. Expression of certain genes is ‘switched on’ in certain cells, but ‘switched off’ in others.

Transferring genes between organisms

• Genetic engineering is a technique used to transfer genes from one organism to another.

• A vector, which is another DNA molecule, is needed for the transfer of genes.

• Circular DNA called plasmids from bacteria can be used to transfer genes.

• After the gene is transferred, the gene can be expressed in the recipient organism.

Genetic engineering and human health

• Bacteria can be made to express human genes and to produce important peptides/proteins, such as insulin.

• A gene for insulin peptide can be transferred from human cells to bacterial cells.

• The bacteria that acquires the foreign gene is known as a transgenic organism / transgenic bacterium.

• The bacterial cells can multiply quickly, producing similar bacterial cells containing the plasmid with the foreign gene.

Genetic engineering method

A human chromosome containing the insulin gene is obtained.

• Both ends of the insulin gene is cut from the human chromosome using a restriction enzyme.

• This enzyme cuts the two ends of the gene to produce ‘sticky ends’ , which is a single strand sequence of DNA bases.

• These bases can pair with complementary bases to form a double strand.

1insulin gene

cut by restriction enzyme

sticky end

fragment of DNA containing the insulin gene

Genetic engineering method

A plasmid from a bacterium is obtained.

• The plasmid is cut with the same restriction enzyme. This produces complementary sticky ends.

The plasmid is mixed with the DNA fragment containing the insulin gene. DNA ligase is added to join the insulin gene to the plasmid.

E. coli bacteria is allowed to take up the plasmids by applying temporary heat or electric shock. This opens up the pores in the cell surface membrane of the bacterium for the plasmid to enter.

2

3

4

plasmid

cut by same restriction enzyme

sticky ends

insulin gene inserted into plasmid

insulin gene

E. coli transgenic bacterium

bacterial DNA plasmid

Biotechnology• Bacteria carrying important human genes for therapeutic

purposes are cultured.

• This means that they are grown in conditions that allow them to multiply and produce the required proteins.

• Bacteria are cultured in fermenters, which are large sterile steel containers closed at both ends.

• Fermenters are designed to keep its internal environment optimum for the desired biological process to operate.

• Note that insulin production by transgenic bacteria is not a fermentation process.

Large-scale fermenters

Transferring foreign genes into plants

• Genes may be inserted into a crop plant which makes it resistant to herbicides or pests.

• The plant which has acquired the foreign gene is a transgenic plant.

• For example:

A gene from a soil fungus produces an enzyme, cyanamide hydratase that converts cyanamide from herbicides to urea. This gene can be inserted into a tobacco plant, thus rendering the plant not only resistant to herbicide, but the urea formed also provides a source of nitrogen for plant growth.

Transferring genes within the same species

• Genes that confer/give resistance to pests can be cut from a wild plant and inserted into a crop plant.

• Healthy genes can also be transferred from a person to another person with defective genes. This is called gene therapy.

• Gene therapy is used to treat diseases like the lung disease cystic fibrosis.

Comparing selective breeding to genetic engineering

Selective breeding Genetic engineering

Organisms involved in selective breeding must be of the same species or be closely related.

Genes from an organism can be inserted into non-related species or different species.

There is a possibility that defective genes can be transmitted to the offspring.

Selection of genes before transfer eliminates the risk of transferring a defective gene.

Slow process that involves several generations

A process which uses individual cells that reproduce rapidly in a small container in a laboratory.

Less efficient as organisms grow more slowly and require more food

More efficient as transgenic organisms grow faster and require less food

Benefits of genetic engineering

Applications of genetic engineering

Benefits to society

Low cost production of medicines

With drugs like human insulin becoming more affordable, more patients can get access to them and be treated.

Production of crops that grow in extreme conditions

This allows farmers to grow crops even when the soil or environmental conditions are not suitable for cultivating most crops.

Development of • crops that produce toxins;• pesticide-resistant crops

The use of costly pesticides that may damage the environment is reduced.

Development of foods designed to meet specific nutritional goals

Improved nutritional quality of foods

Disadvantages of genetic engineering

Environmental hazards

• Genetically-modified (GM) crop plants that produce insect toxins may result in the deaths of insects that feed on them and may result in loss of biodiversity.

• Insects that feed on GM crops my develop resistance to the toxins in the crops and may subsequently develop resistance to pesticides.

• Herbicide-resistant GM crops could cross-breed with weeds to create ‘superweeds’.

Disadvantages of genetic engineering

Economic hazards

• GM seeds can be legally protected against piracy through patenting.

• A patent prevents unauthorised planting of the seeds and prevents other biotechnology companies from producing the same type of GM seeds.

• Companies have engineered crop plants that produce seeds that cannot germinate (terminator technology). Farmers have to buy special seeds from these companies every year.

• In poorer societies, farmers may not have the financial capacity to buy these seeds.

Disadvantages of genetic engineering

Health hazards

• Genetic engineering could introduce allergens, which are substances that cause a reaction in a person’s immune system to the body, into food.

• Genetically modifying plants could result in alteration in metabolic processes within the plants and cause production of toxins.

• Genes that code for antibotic resistance may be incorporated into bacteria that causes diseases to humans.

• Some people may create new combinations of genes for chemical or biological warfare.

Disadvantages of genetic engineering

Social and ethical hazards

• In gene therapy, a gene inserted into the body cells may find its way into the ova or sperms. This gene could mutate and affect the offspring of the patient.

• Genetic engineering may lead to class distinctions.

• Some religions do not approve of genetic engineering as it may not be appropriate to alter the natural genetic make-up of organisms.

True or false

• A foreign gene can be inserted into a plasmid.

• Bacterial cells that do not take up the plasmids containing the insulin gene cannot produce insulin.

• Transgenic bacteria can be grown in fermenters.

• Genetic engineering is always beneficial and has no disadvantages.

• Selective breeding is a faster process than genetic engineering.