Video Transcript
Why is it beneficial for restriction enzymes to leave sticky ends? (A) Leaving sticky ends means that the restriction enzyme can easily recognize that sequence if it needs to be cut again. (B) Fragments of DNA with sticky ends can have their sequence of bases altered more easily than those without. (C) Fragments of DNA cut with the same restriction enzyme can be joined by their complementary bases. (D) Fragments of DNA that have sticky ends are easier to replicate than those without.
This question is asking us about restriction enzymes. Let’s review what these are and how they can be used to manipulate DNA.
Restriction enzymes are useful tools in biotechnology because they can be used to cut specific DNA sequences so they can be combined in interesting ways. They were originally discovered in bacteria as a mechanism to defend themselves from viral infection. Restriction enzymes can do this by cutting viral DNA into pieces, so the virus is restricted from carrying out its life cycle. There are many different restriction enzymes, and each has its own target DNA sequence that it recognizes and cuts. This is called a recognition sequence.
The recognition sequence for the restriction enzyme BamHI is shown below. In addition to having a unique recognition sequence, restriction enzymes also have specific cutting patterns that we can see here as this dotted black line. After the sequence is cut, it will leave two fragments. You’ll notice that there are two overhangs that are generated after BamHI cuts DNA. These are unpaired bases that have an affinity for each other because these bases are complementary. Because these unpaired bases are complementary and can base-pair, they’re called sticky ends.
Sticky ends can be very useful because they allow us to combine DNA from different sources. Here you can see two different DNA sequences that can be combined to form the circular DNA molecule. Because these sequences were both cut with BamHI, they have complementary sticky ends that can pair with each other, allowing one sequence to be inserted into another.
Going back to our question, the option that correctly identifies why it’s beneficial for restriction enzymes to leave sticky ends is given by answer choice (C). Fragments of DNA cut with the same restriction enzyme can be joined by their complementary bases.
