Video Transcript
The mechanism of HpaI is
demonstrated in the diagram provided. What term is given to the cuts that
HpaI leaves?
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 viral infection. 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.
Restriction enzymes can cut their
recognition sequence in different ways. Let’s look at this in more
detail. One way is by producing sticky
ends. The restriction enzyme EcoRI
recognizes the sequence GAATTC and cuts this sequence as indicated by the dotted
black line. When this sequence is cut, two
overhangs of unpaired nucleotides form. These have an affinity for each
other because they can form complementary base pairs with each other. For this reason, these overhangs
are called sticky ends.
If two different sources of DNA are
both cut with the same restriction enzyme, then the fragments will have compatible
sticky ends that can be combined to make new genetic information. The other type of cut that can be
made by restriction enzymes is called a blunt end cut. This is what we see in the provided
diagram on the left. After cutting with HpaI, we have
two blunt end fragments. There are no sticky ends produced
here. Therefore, the type of cuts that
the restriction enzyme HpaI leaves are blunt end cuts.
