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Question 1 of 4genetic engineering / recombinant DNA technology
In genetic engineering, a plasmid and a human gene are cut with the same restriction enzyme so that their cut ends are complementary. Which enzyme is then used to join (splice) the human gene into the cut plasmid to form a recombinant plasmid?
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Model answer: DNA ligase
Explanation: After the plasmid and the human gene are cut with the same restriction enzyme, their matching sticky ends can base-pair with each other. DNA ligase then catalyses the formation of phosphodiester bonds in the sugar-phosphate backbone at these joins, sealing the human gene into the plasmid to form a single recombinant molecule.
Question 2 of 4genetic engineering / recombinant DNA technology
A recombinant plasmid carrying an antibiotic resistance gene is used to transform bacterial cells. Which of the following is a standard method for identifying which bacterial colonies have successfully taken up the recombinant plasmid?
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Explanation: The recombinant plasmid carries a gene for resistance to a particular antibiotic. If transformed bacteria are grown on a medium containing that antibiotic, only cells that took up the plasmid express the resistance gene and survive, while untransformed cells are killed. Gram stain reaction, colony growth rate or size, and cell shape are not affected by plasmid uptake, so none of them can distinguish transformed from untransformed colonies.
Question 3 of 4recombinant DNA technology
During the formation of recombinant DNA, an mRNA molecule for the required gene is isolated and an enzyme is used to synthesise a complementary DNA (cDNA) copy of it. Which enzyme carries out this conversion of mRNA into cDNA?
CorrectNot quite
Model answer: reverse transcriptase
Explanation: Reverse transcriptase uses an mRNA strand as a template to synthesise a single strand of complementary DNA (cDNA), which is then made double-stranded. This lets a eukaryotic gene be obtained without its introns, since the mRNA has already been spliced.
Question 4 of 4recombinant DNA technology
In recombinant DNA technology, both the DNA containing the required gene and the vector (e.g. plasmid) DNA must be cut at specific recognition sequences into fragments before the gene can be inserted into the vector. Which type of enzyme cuts DNA in this way?
CorrectNot quite
Model answer: restriction endonuclease
Explanation: Restriction endonucleases recognise specific short DNA sequences and cut the DNA at those points, producing restriction fragments. Using the same restriction enzyme on both the donor DNA and the plasmid produces complementary cut ends, so the isolated gene can be inserted into the cut vector.