Paper 2 · Genetic Engineering
The same restriction enzyme is used to cut both the plasmid and the gene to be transferred because this produces
Ablunt ends on both fragments, so that the two pieces of DNA can be pushed together without any base pairing
Bsingle stranded RNA copies of the gene, which are read directly by the bacterial ribosomes
Ccomplementary sticky ends, so the cut fragments can pair up by hydrogen bonding between exposed bases
Dshorter DNA fragments, which pass more easily through the pores of the bacterial cell wall
Explanation: A staggered cut leaves a few unpaired bases projecting from each end. If the plasmid and the gene were cut by the same enzyme, those projections are complementary, so the gene slots into the opened plasmid and the bases hydrogen bond together.
Derived from ZIMSEC Biology Paper 2, Nov 2004, Q3