Genetic Engineering

Question 1

What is recombinant DNA?

Answer 1

It is DNA formed by joining together DNA from different sources

Question 2

What is genetic engineering?

Answer 2

• genetic engineering usually involves extracting a gene from one organisms and then inserting it into another organism often one from a different species
• genes can also be manufactured instead of extracting from an organism
• the organism with the inserted gene will then produce the protein coded for by that gene
• an organism that has been genetically engineered to include a gene from a different species is sometimes called a transgenic organism

Question 3

Describe how an organism is genetically engineered

Answer 3

1. The DNA fragment containing the gene you want is isolated using restriction enzymes (see flash card on restriction enzymes)
2. The DNA fragment with the gene in is inserted into a vector
   - the DNA fragment is inserted into a vector (something that is used to transfer DNA into a cell) –> they can be plasmids (small, circular molecules of DNA in bacteria) or bacteriophages (viruses that infect bacteria
   - the vector DNA is cut open using the same restriction enzyme that was used to isolate the DNA fragment containing the desired gene
   - so the sticky ends of the vector are complementary to the sticky ends of the DNA fragment containing the gene
   - the vector DNA and DNA fragment are mixed together with DNA ligase, the base pairs anneal and DNA ligase joins up the sugar phosphate backbones of the two bits, this is called ligation
   - the new combination of bases in the DNA is called recombinant DNA
3. The vector transfers the gene into the bacteria
   - the vector with the recombinant DNA is used to transfer the gene into bacterial cells
   - if a plasmid vector is used the bacterial cells have to be persuaded to take in the plasmid vector and its DNA
   - -> they’re placed into a freezing calcium chloride solution to make their walls more permeable
   - -> the plasmids are added and the mixture is heat-shocked (heated to around 42 degrees for 1-2 minutes, this encourages the cells to take in the plasmids
   - if a bacteriophage vector is used, the bacteriophage will infect the bacterium by injecting its DNA into it, the phage DNA then intergrates into the bacterial DNA
   - cells that take up the vectors containing the desired gene are genetically engineered so are called transformed
4. Identify the transformed bacteria
   - not all the bacteria will have taken up the vector so marker genes can be used to identify the ones that have
   - marker genes can be inserted into vectors at the same time as the desired gene, this means any transformed bacterial cells will contain the desired gene and the marker gene
   - the bacteria are grow on agar plates and each cell divides and replicates its DNA, creating a colony of cells
   - transformed cells will produce colonies where all the cells contain the desired and the marker gene
   - the marker gene can code for antibiotic resistance - bacteria are grown on agar plates containing the antibiotic so only cells that have the marker gene will survive and grow
   - the marker gene can code for fluorescence - when the agar plate is under a UV light only transformed cells will fluoresce

Question 3

What are the advantages of microorganisms being able to take up plasmids?

Answer 3

• it is beneficial as the plasmids can contain useful genes, this means the microorganisms gain useful characteristics so they’re more likely to have an advantage over other microorganisms which increases their chance of survival
• plasmids can contain genes that code for resistance to antibiotics
• genes that help microorganisms invade hosts
• genes that mean microorganisms can use different nutrients

Question 4

Outline the process of genetically engineering bacteria to produce human insulin

Answer 4

• the gene for human insulin is identified and isolated using restriction enzymes
• a plasmid is cut open using the same restriction enzyme that was used to isolate the insulin gene
• the insulin gene is inserted into the plasmid forming recombinant DNA
• the plasmid is taken up by bacteria and any transformed bacteria are identified using marker genes
• the bacteria are grown in a fermenter and human insulin is produced as the bacteria grown and divide
• the human insulin is extracted and purified so it can be used in humans

Question 5

Outline the process of genetically engineering golden rice

Answer 5

• the psy gene from maize and the crtl gene from the soil bacteria are isolated using restriction enzymes
• a plasmid is removed from the Agrobacterium tumefaciens bacterium and cut open with the same restriction enzymes
• the psy and crtl genes and a marker gene are inserted into the plasmid
• the recombinant plasmid is put back into the bacterium
• rice plant cells are incubated with the transformed A.tumefaciens bacteria which infect the rice plant cells
• A.tumefaciens inserts the genes into the plant cells DNA creating transformed rice plant cells
• the rice plants are then grown on a selective medium and only transformed rice plants will be able to grow because they contain the marker gene that’s needed to grow on this medium

Question 6

What is golden rice?

Answer 6

• it is a type of genetically engineered rice, the rice is genetically engineered to contain a gene from a maize plant and a gene from a soil bacterium which together enable the rice to produce beta-carotene
• the beta-carotene is used by our bodies to produce vitamin A
• golden rice is being developed to reduce vitamin A deficiency in areas where there’s a shortage of dietary DNA