Video Transcript
What is the role of restriction enzymes in forming recombinant DNA? (A) To join gaps in the sugar–phosphate backbones of combined DNA. (B) To form strands of DNA that are complementary to the mRNA taken from an organism. (C) To form a strand of DNA that is complementary to a DNA template strand. Or (D) to cut sections of DNA, leaving sticky ends to allow recombination.
To answer this question, we have to understand what recombinant DNA is. Recombinant DNA is DNA combined from two or more sources. A classic example is how the gene for human insulin can be inserted into bacterial DNA. This makes recombinant DNA that can then be transferred in the bacterial cells so they can make human insulin. In order to combine these two DNA sources, we need a way to cut DNA sequences so they can be inserted into other DNA sequences.
So suppose we have these two sequences as shown here. In order to cut these sequences, we can use a special group of enzymes called restriction enzymes. Restriction enzymes recognize certain DNA sequences and then cut the DNA at that sequence. After cutting, there are DNA bases that are unpaired. These are called sticky ends. Only one sticky end is shown for both the insulin gene and bacterial DNA for simplicity, but there is another unpaired sticky end produced also. If we use the same restriction enzyme for both the insulin gene and the bacterial DNA, then two compatible sticky ends can come together for recombination. Again, only one side is shown here for simplicity.
Therefore, the role of restriction enzymes in forming recombinant DNA is given by answer choice (D), to cut sections of DNA, leaving sticky ends to allow recombination.
