COAS Biology 2 Teacher Resources Original Material Cambridge University Press 2009 2

11 Activity

Genetic engineering

Read the following passage and then answer the questions that follow. 1 The aim of genetic engineering is to remove a gene from one organism and transfer it into another so that the gene is expressed in its new host and the product can be harvested and used. Genetic engineering has been particularly useful in the production of humulin (human insulin) for the treatment of diabetes. In genetic engineering, there are three different ways of obtaining the 5 desired gene. In the first method, the DNA (gene) can be made in the laboratory using the genetic code. The second method makes complementary DNA (cDNA) by using the mRNA transcript, and the third method isolates the actual gene from the genome using restriction endonuclease enzymes. This last method usually leaves complementary overlapping ends. For the other two methods, nucleotides can be added to give the same effect. Next, a carrier is used to transfer the 10 DNA into the host. A plasmid is a small circular DNA molecule, which can act as a carrier when the gene is to be inserted into a host bacterial cell. The plasmid is cut, using the same restriction enzyme used to isolate the gene. When mixed with the gene and another enzyme, recombinant plasmids can be formed. Usually, the plasmid contains two antibiotic resistance genes (e.g. against tetracycline and ampicillin), which can be used as markers. When the gene splicing has been 15 successful, one of the two resistance genes is destroyed (e.g. against tetracycline). The plasmid, gene and enzyme mixture is then added to a culture of host cells, such as Escherichia coli bacteria, and a small proportion of the bacteria will successfully take up the recombinant plasmids to become recombinant host cells. The bacteria are transferred to culture plates containing antibiotic (e.g. ampicillin) and then replica plated onto plates containing the other antibiotic (tetracycline). 20 By comparing the growth of bacterial colonies on the two plates, those which contain the recombinant plasmid can be selected and then cultured in a fermenter. Many identical copies of the gene are obtained when the bacteria replicate, allowing more product to be harvested.

Questions 1 What kind of organic chemical is the gene product, insulin, composed of (line 3)? [1] 2 In insulin production, which method (lines 5–8) is employed to obtain the insulin gene? [1] 3 Name i the organ, ii the part of the organ, and iii the type of cell that produces insulin. [3] 4 What must be known about the gene product before the first method can be used to obtain a gene (lines 5–6)? [1] 5 In the second method, name the enzyme that is used to synthesise single-stranded cDNA from mRNA (line 6). [1] 6 What enzyme would be used to obtain double-stranded DNA from single-stranded cDNA? [1] 7 What is missing from the gene produced in the second method that would be present in a human gene obtained by the third method (lines 6–8)? [1] 8 What is another term for complementary overlapping ends (line 8)? [1] 9 Explain how it will be useful to have complementary overlapping ends when plasmid and gene are mixed (lines 8–9). [2] 10 What is the general term for a carrier of the gene into the host (lines 9–10)? [1]

COAS Biology 2 Teacher Resources Original material © Cambridge University Press 2009 1 11 What is the name of the enzyme that is placed in the plasmid–gene mixture (line 12)? [1] 12 What is the function of this enzyme? [1] 13 What do you understand by the term recombinant (lines 12, 17, 18)? [2] 14 Suggest how one of the two resistance genes is destroyed (line 15). [1] 15 Which plate will contain bacterial hosts with recombinant plasmid, those with ampicillin or those with tetracycline (lines 20–21)? [1] 16 Give a term that means producing many identical copies of the gene (lines 21–2). [1]

Total: Score: % 20