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There are a lot of labs in biology that are
super memorable, as I’ve mentioned before,
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but I remember this one where we had these
bacteria and we gave the bacteria a gene from
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a different organism.
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It came from a jellyfish- specifically a bioluminescent
jellyfish.
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Its gene that was taken up by the bacteria
gave the bacteria the ability to have this
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glowing appearance if put under the UV light.
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Like the jellyfish.
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How wild is that?
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It was a neat lab to do once I became a teacher
too – this is actually a very popular lab
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in advanced biology courses.
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But naturally, everyone kept wanting to know,
“Is it possible for bacteria to be given
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a human gene?
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Not just one from a jellyfish?”
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The answer to this class question is yes!
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And that’s when I got to talk about how
insulin is produced.
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Insulin is a hormone that all humans need;
it is made by the pancreas.
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The hormone insulin helps make sure that cells
get the glucose they need.
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But Type 1 Diabetes is a condition where the
pancreas doesn’t make enough insulin, and
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therefore the individual must take insulin,
usually in the form of an injection.
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So how is insulin produced in the lab setting
so that those with Type 1 Diabetes will have
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an adequate amount of insulin to inject?
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Well one current and common way today is by
using bacteria in a lab.
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These bacteria in a lab can be given the human
gene for insulin and then the bacteria produce
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the insulin.
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Lots of benefits on that: bacteria are relatively
easy to grow, multiply quickly, don’t take
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up a ton of space.
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Both the jellyfish and insulin scenarios are
examples of transformation, which is the process
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where a cell – commonly bacteria - can take
up DNA from their environment and use that
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DNA.
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Transformation can occur in nature but these
transformations were specifically performed
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using genes of interest from other organisms.
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These two examples fall under the topic of
our video: genetic engineering.
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Genetic engineering can be very generally
defined as changing an organism’s genotype
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using biotechnology tools or techniques.
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Let’s focus more on the whole bacteria producing
insulin example to illustrate how this was
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done.
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Focusing first on some basics that we know:
here is a human cell.
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Like most cells in your body, it contains
a nucleus.
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And like most body cells, that nucleus contains
the organism’s entire DNA code.
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With some exceptions, each body cell you have
contains all of your DNA.
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If you recall, genes are made of DNA and so
there is a gene that codes for making the
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protein insulin in most of your body cells.
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While this gene could be removed from a cell’s
DNA, the gene for insulin can also be synthesized
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in a lab.
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This insulin gene can be inserted into a bacterial
plasmid.
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A plasmid is like an extra set of genes – in
addition to the bacterial chromosome - that
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bacteria can use.
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Plasmids tend to be in a circular shape.
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Plasmids are common in bacteria; you can also
find them in yeast cells.
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But to get specific DNA into the plasmid,
you have to make space for that.
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For that, you can use restriction enzymes.
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Restriction enzymes are enzymes that cut in
specific spots---like teeny tiny scissors---and
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can cut a specific spot in the plasmid so
you can add in that human insulin gene.
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Ligase ---you remember ligase from our DNA
replication video --- can be used to help
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seal it into place.
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This is now considered recombinant DNA because
it contains not only the plasmid DNA but also
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the DNA of interest, the gene for producing
insulin.
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The recombinant DNA is made up of DNA from
different sources.
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In order to encourage a bacterium to pick
up the plasmid in transformation, certain
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chemicals and temperature changes may be used.
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Once it picks up that plasmid, when the bacterium
reproduces by splitting, the resulting cells
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will both inherit the plasmid.
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And then their daughter cells will inherit
it.
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And theirs.
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You get the picture.
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In this way, the plasmid continues to be produced
over and over.
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The bacteria can use the human insulin gene
to produce human insulin and the insulin can
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be purified in a lab setting to be used for
humans.
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Let’s talk about some vocab in our example.
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In this example of genetic engineering, the
bacteria were genetically modified from recombinant
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DNA.
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You can consider the bacteria to be transgenic:
any organism or microorganism that has genetic
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material from some other organism is considered
transgenic.
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The plasmid was the vector in this situation.
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A vector can be thought of as the vehicle
for getting the recombinant DNA into the organism.
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Plasmids are a common vector.
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But plasmids aren’t the only vectors in
genetic engineering.
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Viruses are another example.
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If a virus’s own genetic material is removed
and a gene of interest instead is placed inside,
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the virus can then be permitted to attach
to target cells to deliver that gene of interest.
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When it attaches to a target cell, it inserts
the gene of interest.
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Viruses in this way are another delivery system.
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And viruses can target any kind of living
cell: bacteria, fungi, plants, animals – including
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humans.
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You can find examples with viruses in our
description.
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Sometimes if the plasmid or viral vector is
just not ideal for delivering DNA into a cell
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– well you have more options.
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There’s microinjection.
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A special kind of micropipette can inject
the gene of interest through the cytoplasm
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of a cell and into its nucleus.
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For example, if the target was a fertilized
mouse egg cell.
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Or- and I didn’t learn about this until
more recently - gene guns.
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Yes, really.
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A gene gun can shoot particles – gold particles
for example – that are coated with DNA
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Really helpful in cases where you have thick
cell walls to get through, like a plant cell.
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Genetic engineering techniques and tools continue
to develop and change So when we were taking
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about restriction enzymes, and we mentioned
they cut in specific spots: they have certain
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sites they recognize and anytime that site
exists, they cut.
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Restriction enzymes are actually part of the
natural defense system bacteria have against
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bacteriophages; they can chop up bacteriophage
DNA.
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But what if you had a way to customize the
exact place you want to cut in DNA?
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Perhaps you’ve heard about CRISPR?
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This gene editing tool allows for the editing
of DNA using a special kind of nuclease called
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Cas9.
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Recall that nucleases, like restriction enzymes
and Cas9, can cut DNA and like restriction
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enzymes, the CRISPR-Cas9 system is also part
of the natural defense system bacteria have
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against bacteriophages.
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But in CRISPR, by using a specific guide RNA
that can be designed in the lab, the Cas9
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can be guided with the specific guide RNA
to cut at points around a specific target
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gene.
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And by doing that, one can do gene editing
by removing a selected target gene –and
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if desired, a new gene could be inserted in
its place.
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CRISPR has been used in plants and animals
including clinical trials of humans.
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So now that we’ve covered some ways that
genetic engineering can be done, we want to
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address: how can genetic engineering be useful?
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There are tons and tons of examples of uses
for genetic engineering so just picking a
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few here:
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First, there’s use in the medical field.
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Producing insulin for those that cannot is
an example we mentioned and currently pharmaceutical
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companies also use genetic engineering to
make clotting factors, human growth hormone,
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and more.
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There’s genetic engineering in agriculture
– for example, genetically engineered crops
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that might better resist insect pests or herbicides
or drought.
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There’s genetic engineering research being
done for developing plants that could remove
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pollutants from the air or soil.
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And an example with animals?
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There’s work being done in genetic engineering
to develop chickens that are resistant to
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avian influenza, aka bird flu.
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Genetically engineered mice are often used
in research to better understand certain gene
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functions.
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However, with these examples we’ve outlined
and more, it’s important to mention there
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are also ethical considerations for genetic
engineering that must be examined and considered.
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Depending on the type of genetic engineering
being performed this could involve animal
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welfare or ecological concerns or equity in
access: again, those are just a few examples
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among many.
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We’ve included sources of bioethics involving
genetic engineering in our description.
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If the field of genetic engineering interests
you, just know that the career of a genetic
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engineer is a career that is expected to keep
on growing.
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Well, that’s it for the Amoeba Sisters,
and we remind you to stay curious.
