Video Transcript
The diagram provided shows a basic
outline of the process used to form recombinant DNA. In this process, what acts as the
vector?
This question provides a diagram
outlining the process used to form recombinant DNA. In order to answer this question,
we need to review some basic terminology that relates to forming recombinant
DNA.
First of all, what is recombinant
DNA? Recombinant DNA is the combination
of DNA from at least two different sources. Just like in the provided diagram,
we can see one source of DNA from this bacterium here and the other from a human
chromosome. The bacterial DNA, shown in orange,
is combined with the human DNA, shown in green. This bacterial DNA is a special
type of DNA called a plasmid. Plasmids are extrachromosomal
pieces of bacterial DNA, meaning they’re separate from the bacterial chromosome. Plasmids can carry accessory genes,
like antibiotic resistance, that can help bacteria adapt to their environments. They replicate independently of the
bacterial chromosome.
These two sources of DNA are
combined to form the recombinant DNA that we can see here. You’ll notice that in order to form
recombinant DNA, the DNA from these two sources needs to be cut. To cut DNA, we use special enzymes
called restriction enzymes. Restriction enzymes can recognize
specific sequences of DNA, called recognition sequences, and cut at that
sequence. For instance, the restriction
enzyme EcoRI cuts at the site GAATTC, which we can see boxed here. When EcoRI cuts DNA, it cuts it in
a specific way. So this is how DNA sequences are
cut when forming recombinant DNA.
But how do we make two different
pieces stick back together? After the sequence is cut, you’ll
notice that there’s overhangs or regions of unpaired DNA bases. These are called sticky ends
because they have a tendency to stick back together due to the complementary base
pairs. So if we cut our bacterial plasmid
DNA and human DNA with the same restriction enzyme, we can bring them together
because of their complementary sticky ends. On the diagram on the left, we can
see the sticky ends on the cut human DNA indicated here with the green arrows. And we can see the sticky ends on
the cut plasmid DNA indicated here with the orange arrows. Because these ends are
complementary, since they were cut with the same restriction enzyme, they can be
joined together, as we can see indicated here by the pink arrows.
This recombinant DNA can then be
transferred back into bacterial cells in a process called transformation. And the bacterial cells can go on
to divide and make more copies of this recombinant DNA. We can see this in the diagram on
the bottom. During this process, which is
collectively known as DNA cloning, we use bacterial plasmid DNA to insert a gene of
interest from human DNA. This way, the human DNA can be
expressed in bacterial cells. This can be very useful for
producing certain therapeutics, for instance, insulin.
Because the bacterial plasmid DNA
is carrying the gene of interest, it is also known as a vector. Therefore, in forming recombinant
DNA in this diagram, the bacterial plasmid acts as the vector.
