Fig. 1 shows a plasmid being used to make bacteria that produce a human blood-clotting protein. A laboratory team cut the plasmid and a human DNA sample wit...
Question 1 Report
Fig. 1 shows a plasmid being used to make bacteria that produce a human blood-clotting protein. A laboratory team cut the plasmid and a human DNA sample with the same restriction enzyme. The modified bacteria were grown in a fermenter at 30 degrees C with oxygen and nutrients. Table 1 shows the mass of protein collected after different growth times.
Table 1
| Growth time / h | Protein mass / mg |
|---|---|
| 10 | 18 |
| 20 | 46 |
| 30 | 75 |
| 40 | 77 |
(a) Name the enzyme used to join the human gene into the plasmid. [2]
(b) Describe the change in protein mass between 20 h and 40 h. [2]
(c) Use Fig. 1 to suggest why bacteria are suitable cells for producing this protein. [2]
(d) Suggest one way the team could reduce the risk of bacteria entering the water supply from the fermenter. [2]
Answer Details
(a) The enzyme is DNA ligase. It joins, or seals, the sugar-phosphate backbone of DNA after the human gene has been inserted into the plasmid. [2]
(b) Protein mass increased from 46 mg at 20 h to 77 mg at 40 h:
\[77-46=31\text{ mg}\]
The increase was 31 mg. The results also show that production levels off after 30 h, rising only from 75 mg to 77 mg. [2]
(c) The plasmid acts as a vector, carrying the human gene into bacterial cells. Bacteria reproduce rapidly, producing many cells that can make the required protein. [2]
(d) The fermenter should be sealed to prevent bacteria escaping. Waste should also be sterilised before release, or passed through filters, so bacteria cannot enter the water supply. [2]
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