Genetic modification (genetic engineering)

What is genetic modification?

It is the removal of a gene from one organism and its insertion into the DNA of another organism often of a different species so that the gene is expressed.

What is the role of restriction enzymes in genetic modification?

Restriction enzymes are used to cut the DNA molecules at specific points called recognition sites.

The restriction enzymes mostly cut the DNA to leave a staggered cut known as sticky ends.

The same restriction enzyme is used to cut out the vector which could be a virus or a plasmid from bacteria.

What are recognition sites?

Recognition sites are a short sequence of bases specific to the restriction enzyme

What are sticky ends?

They are short single stranded lengths of exposed bases.

The sticky end of the useful gene is complementary to the sticky end of the vector.

What is the role of ligase in genetic modification?

Ligase enzymes are used to catalyse the joining of cut ends of DNA molecules together or the joining of two sticky ends.

What are the two vectors used in genetic modification?

• Viruses - the required gene is inserted into the protein coat of the virus to protect it.

(Viruses that don’t cause diseases are used to infect the cell so that the gene can be inserted into it’s DNA)

• plasmids from bacteria

Vectors take up pieces of DNA and insert the recombinant DNA into other cells.

How can large amounts of insulin be manufactured from genetically modified bacteria and are grown in a fermenter?

1. Gene for human insulin is identified in human DNA and cut out using a restriction enzyme.

2. Many copies of gene is made.

3. Bacterial plasmids are extracted and cut open using the same restriction enzyme.

4. A ligase enzyme is used to join the plasmid and the gene together, forming recombinant plasmids.

5. The bacteria are incubated with the recombinant plasmids using a heat shock and calcium ions.

6. The transformed bacteria will produce human insulin and the bacteria are tested to check if they contain the recombinant DNA. If not, they are discarded.

7. The genetically modified bacterial cells are grown in fermenters which contain all the substance needed for them to grow and multiply.

8. The bacterial cells reproduce asexually and rapidly, producing large amounts of insulin

9. The insulin in the bacterial cells is separated and purified.

What are the advantages of using genetically engineered insulin?

• produce lots of insulin rapidly

• less rejection as human insulin gene is used

• more ethical, suitable for vegetarians/ vegans/ people who cannot use pig due to religious reasons

• not worried about contracting diseases from pigs

List some uses of genetically modified bacteria.

• Human insulin — to treat people with type 1 diabetes

• human vaccines

• human growth hormones

• enzymes in the food industry

• enzymes from washing powder

What is the bacterium involved in genetic modification of plants?

Agrobacterium tumefaciens

It naturally infects plants and produce a cancerous growth (tumour) called a crown gall.

How can genetically modified plants improve food production?

1. Agrobacterium is used as a vector as it contains a small loop of DNA [Ti plasmid (tumour inducing)].

2. Restriction enzyme (restriction endonuclease) is used to cut out the desired gene and then cut open the bacterial plasmid.

3. Desired gene is inserted into Ti plasmid where DNA ligase is used to join the resistance gene and plasmid together.

4. plasmid containing desired gene is put in Agrobacterium tumefaciens

5. Bacterium infects plant or isolated leaf discs, causing the infected plant to produce a crown gall

6. The cells of the gall each contain a Ti plasmid with the desired gene, so pieces of tissue cut from the crown gall are cultured

7. The gall cells grow into plants that express the desired gene (e.g. resistant to herbicides)

What are the advantages of creating herbicide resistant plants?

• Farmers can use one heavier dose of herbicide instead of several small doses

• increase crop yield

• can just target weeds, killing the competition

What are the disadvantages of creating herbicide resistant plants?

• could lead to development of herbicide resistant weeds

• loss of biodiversity - loss of food and shelter for animals

• different weeds or invasive species could take place of removed weeds

List some uses of genetically modified plants.

• Plants resistant to herbicides

• Plants resistant to frost

• Fruit and vegetables with longer shelf life

• Plants producing antibodies and antigens

• Increased resistant to range of pests and pathogens

These all improve food production.

What are the advantages of producing golden rice?

• Contains beta carotene used to make vitamin A in the body

• saves people with a vitamin A deficiency

• prevents night blindness and scarring of cornea

What are the disadvantages of producing golden rice?

• people who suffer a vitamin A deficiency may not be able to afford

• plants may not yield fertile seeds - new seeds must be bought each year

• concerns over safety of consuming genetically modified plants

• chance of crossbreeding with wild rice plants - contamination of DNA

Define the term transgenic.

The transfer of genetic material from one species to another species where the gene is inserted into the DNA of a nucleus before it is placed in an enucleated egg cell.

List some uses of cloned transgenic animals

• research

• drug production

• organ production for transplantation (Xenotransplantation)

• increased production of a particular product (e.g. higher milk yield)

• animals with increased resistance to diseases and parasites

List some concerns over the use of cloned transgenic animals.

• welfare of animal

• expensive

• organs might carry diseases

• unethical

List some risks associated with xenotransplantation.

• a much greater immune rejection

• may carry pathogens

• viruses could be hidden in the DNA