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
The above mRNA sequence is responsible for coding for 6 amino
• During translation, the ribosome moves along the mRNA.
• In controlling the genes, cells will control the amount of proteins they
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.
• 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
• 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
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
cut by restriction
fragment of DNA containing the insulin gene
Genetic engineering method
A plasmid from a bacterium is
• 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.
cut by same
insulin gene inserted
E. coli transgenic bacterium
bacterial DNA plasmid
• 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
• Note that insulin production by transgenic bacteria is not
a fermentation process.
Transferring foreign genes
• 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
• 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
• 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
There is a possibility that defective
genes can be transmitted to the
Selection of genes before transfer
eliminates the risk of transferring a
Slow process that involves several
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
Benefits of genetic engineering
Benefits to society
Low cost production of
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.
• 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
Improved nutritional quality of foods
• 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’.
• GM seeds can be legally protected against piracy
• 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.
• 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
• Some people may create new combinations of genes
for chemical or biological warfare.
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
• Selective breeding is a faster process than genetic