A biotechnology company produces human insulin for people with diabetes. Fig. 1 shows part of the method used before the bacteria are placed in large fermen...
Question 1 Report
A biotechnology company produces human insulin for people with diabetes. Fig. 1 shows part of the method used before the bacteria are placed in large fermenters. A copy of the insulin gene is taken from human DNA and placed into a bacterial cell.
(a) Name the small circular DNA molecule used in this method. [1]
(b) Complete the description of the method by stating what is inserted into the cut plasmid and where the recombinant plasmid is placed. [2]
(c) Explain the roles of a restriction enzyme and DNA ligase in producing the recombinant plasmid. [3]
(d) Explain why bacteria that have received the plasmid can provide a large supply of insulin for people. [4]
Answer Details
(a) The small circular DNA molecule is a plasmid. [1]
(b) Insert the insulin gene (insulin DNA) into the cut plasmid. The resulting recombinant plasmid is then placed into a bacterial cell. [2]
(c) A restriction enzyme cuts DNA at a specific base sequence. It cuts the insulin-gene DNA and plasmid so that they have matching ends. DNA ligase then joins and seals the insulin gene into the plasmid, making recombinant DNA. [3]
(d) Bacteria reproduce rapidly by cell division. Each daughter bacterium receives a copy of the recombinant plasmid, including the human insulin gene. The gene is expressed, so the bacteria make human insulin. Very large numbers of bacteria can be grown in fermenters, and the insulin can then be collected and purified for treatment. [4]
Exam focus: Restriction enzymes cut at particular DNA sequences; ligase joins DNA. This makes it possible for a human gene to be copied as bacteria divide.
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