Video Transcript
The diagram provided shows a
fragment of DNA produced from the cutting of a sequence using BamHI. The fragment is left with exposed
nucleotide bases. What term is given to this?
This question is asking us about
restriction enzymes. Let’s review what a restriction
enzyme is 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 way for bacteria to defend themselves from viruses. They 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. This is also present in the
sequence of the provided diagram. In addition to having a unique
recognition sequence, restriction enzymes also have specific cutting patterns that
we can see here as the dotted black line. After the sequence is cut, it will
produce two fragments. You’ll notice that there’s two
overhangs that are generated after BamHI cuts DNA. These are unpaired nucleotides that
have an affinity for each other because the bases are complementary. Because they’re complementary and
can base-pair, they’re called sticky ends.
Sticky ends can be very useful
because you can bring together two different fragments of DNA to combine them. As long as they were both produced
with the same restriction enzyme, they will have compatible sticky ends that can be
joined. So if we look back at this diagram
in the question, we can see that the fragment that is left with exposed nucleotide
bases after cutting with BamHI is called a sticky end.
