Genetically modified organisms and recombinant DNAEdexcel International A Level Biology: Subtopic test

1. 1
   A biotechnology company makes human insulin using the bacterium Escherichia coli. The insulin gene is cut from human DNA using a restriction endonuclease. The same enzyme is used to cut bacterial plasmids. The fragments are mixed and joined, and the resulting recombinant plasmids are put into bacteria that are then grown in large fermenters.

   (a)

   Which enzyme joins the sugar-phosphate backbones of the insulin gene and the cut plasmid?

   [1 mark]

   • ADNA ligase
   • BRestriction endonuclease
   • CDNA polymerase
   • DRNA polymerase

   (b)

   Why is the same restriction endonuclease used to cut both the human DNA and the plasmid?

   [1 mark]

   • ASo that the plasmid is cut in many places
   • BSo that blunt ends are produced on both
   • CSo that the plasmid is no longer circular
   • DSo that complementary sticky ends are produced that can base pair

   (c)

   Suggest two advantages of using genetically modified bacteria to make insulin rather than extracting insulin from pig pancreases.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A research group produces goats that secrete human antithrombin (a protein that prevents unwanted blood clotting) in their milk. The antithrombin gene is joined to a promoter that is active only in mammary gland cells, and the recombinant DNA is injected into fertilised goat eggs, which are then implanted into surrogate mothers.

   (a)

   What is the function of the promoter joined to the antithrombin gene?

   [1 mark]

   • AIt cuts the gene from the human chromosome
   • BIt joins the gene to the goat DNA
   • CIt provides a binding site for RNA polymerase so the gene is transcribed in mammary gland cells
   • DIt is a marker that shows which goats contain the gene

   (b)

   Why is the recombinant DNA injected into fertilised eggs rather than into cells of the udder of an adult goat?

   [1 mark]

   • AThe DNA would not be transcribed in an adult udder
   • BEvery cell of the goat that develops from the egg will contain the gene, and the goat can pass it on to its offspring
   • CFertilised eggs do not have DNA of their own
   • DAdult cells cannot be injected with a needle

   (c)

   Suggest two advantages of making antithrombin in the milk of GM goats.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Researchers want a tobacco plant to make a human antibody for use as a drug. They cut the antibody gene from human DNA and the T-DNA region of the Ti plasmid of Agrobacterium tumefaciens with the same restriction endonuclease. The T-DNA also carries a gene for resistance to the antibiotic kanamycin. Leaf discs are infected with the recombinant Agrobacterium and grown on a medium containing kanamycin, and plants are regenerated from the discs that survive.

   (a)

   Describe how the antibody gene is inserted into the Ti plasmid.

   [3 marks]

   (b)

   (i) Explain how the kanamycin-resistance gene allows the researchers to obtain GM plants. (2 marks)
   (ii) Suggest two reasons why the antibody might be made in tobacco plants rather than in E. coli. (2 marks)

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A pharmaceutical company wants to produce a human blood-clotting protein. The protein is large, has sugar groups attached to it after translation, and is needed in large quantities to treat patients. The company is comparing three production systems: bacteria grown in fermenters, GM sheep that secrete the protein in their milk, and GM tobacco plants grown in fields.

   (a)

   Describe how a recombinant plasmid containing the gene for the protein could be made and introduced into bacteria, and explain how the bacteria that have taken up the plasmid are identified.

   [6 marks]

   (b)

   Evaluate the use of GM bacteria, GM sheep and GM tobacco plants to produce this protein, and conclude which system is most suitable.

   [6 marks]

   Total for question 4: 12 marks

End of questions