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