Gene technology

Sample questions

Original practice questions written in the style of the exam.

1. Question 15 marks

   Describe how bacteria can be genetically modified to produce human insulin.

   Mark scheme

   • The insulin gene is obtained, e.g. by cutting it out of DNA with a restriction enzyme or by making cDNA from mRNA with reverse transcriptase (1)
   • A plasmid is cut with the same restriction enzyme, giving complementary sticky ends (1)
   • The gene and plasmid are joined by DNA ligase to form recombinant DNA (1)
   • The recombinant plasmids are taken up by bacteria (e.g. after heat shock with calcium ions) (1)
   • Bacteria that have taken up the plasmid are identified using marker genes (e.g. antibiotic resistance) and then cultured (1)
2. Question 23 marks

   Explain how a DNA microarray can be used to find out which genes are being expressed in a tumour cell.

   Mark scheme

   • mRNA is extracted from the cell and used to make (fluorescently) labelled cDNA (1)
   • The labelled cDNA is washed over the microarray and hybridises with complementary DNA probes for known genes (1)
   • Spots that fluoresce show which genes were being transcribed; brighter spots indicate higher expression (1)