Video Transcript
In this video, we’ll learn what
genetic engineering means and why it’s important, how some enzymes are actually used
to cut and paste DNA between organisms of different species, take a look at a few
examples applications of this technology, and work a practice problem or two. By the end, we’ll have a basic
understanding of how genetic engineering can be used to solve problems involving
life.
Let’s start with a basic overview
of genetic engineering. Well, a gene is a section of DNA
that codes for a protein generally and can affect one or more traits. And the verb form of engineer means
to design or build. And in the case of genetic
engineering, what generally occurs is really more of a partial rebuild. So genetic engineering has to do
with a partial rebuilding of the genome or genetic information of an organism. But let’s look a little bit
deeper. Thousands of years ago, humans
realized they could change or modify the traits of plants or animals by selecting
the organisms with the traits that they really liked for breeding. This is called selective
breeding.
Over one or more generations,
particular traits can be adjusted, such as flower size as long as the trait has a
genetic basis or, in other words, that the trait is coded for by a gene in the
organism’s DNA. But in the 1970s, biologists
developed a technique referred to as genetic engineering that specifically alters an
organism’s DNA by transferring a gene of choice from one species to another. A common example of this technique
uses a gene from a jellyfish that produces a glow in the dark protein. This gene has been transferred into
several other species, including cats, pigs, and zebrafish.
Making a cat glow is great, since
they do seem to enjoy tripping people, and glowing makes them hard to miss, even in
the dark. But let’s take a look at some other
reasons why genetic engineering has become increasingly common over the past 50
years. Genetic engineering has many
practical applications. In the medical field, it’s used for
gene therapy to produce therapeutic proteins like insulin or antibodies and in
medical research. In agriculture, genetic engineering
has been used to improve crop yields, nutritional content, and resilience to pests,
pathogens, herbicides, and environmental change. In addition, growth rates have been
increased in some animals that are farmed, such a salmon.
Some industries also use genetic
engineering to produce proteins quickly, cheaply, and with less environmental damage
for medical applications, food production, and more. Genetic engineering is also highly
valuable tool in biological research as scientists continue to unravel the mysteries
of life. Let’s review some concepts of DNA
structure, the base pairing rules for DNA, and the genetic code before moving on to
how genes are moved between species.
Let’s take a look at the structure
of DNA first. The shape of DNA is a double helix,
which resembles a twisted ladder. But in this diagram, the twist has
been removed, so we can see the parts more easily. DNA contains deoxyribose sugars,
phosphate groups, and four different types of bases that include adenine, thymine,
cytosine, and guanine. When a DNA molecule is assembled,
small groups called nucleotides that contain a sugar, a phosphate, and a base bond
together to produce the DNA polymer. Nucleotides bond from one base to
another, forming base pairs that can either be from adenine to thymine, or A to T,
or cytosine to guanine, C to G. And these are called the base
pairing roles.
Genes are located along the length
of DNA molecules and are also a lot longer than indicated in our diagram here. The average length of a human gene
is over 8000 base pairs long. The nucleotide sequence in genes
encodes instructions for the order of amino acids and proteins. So if you move a gene from one
organism to another, it enables the organism that receives the gene to make that
particular protein, since the genetic code of DNA is virtually the same in all
species. In the eukaryotic cells of animals,
plants, fungi, and protist, DNA is long and linear and coils into structures called
chromosomes, while the prokaryotic cells of bacteria and archaea contain DNA like
our own but circular. And they can have smaller DNA
molecules called plasmids as well.
And viruses, which can be used in
genetic engineering, are generally considered not alive, but they do have either DNA
or its nucleic acid cousin, RNA. Next, we’ll take a look at how
restriction enzymes can be used in genetic engineering. Next, we’ll take a look at how
restriction enzymes can be used in genetic engineering. Our goal is to produce the protein
hormone insulin, which is a medicine used to treat diabetes. And we wanna produce that insulin
from a population of bacteria. Does a bacterium need to regulate
sugar in its blood? Of course, not. Organisms as small as bacteria
don’t need huge circulatory systems filled with blood. So it doesn’t need and doesn’t
produce the hormone insulin either.
So we need to get the human insulin
gene from a human cell, and then we need something that can carry this gene once
it’s removed from the rest of the DNA around it. The vector is used to carry this
gene into its new home in a bacterial cell. And one commonly used vector is a
plasmid, the small circular DNA molecule that’s normally found in prokaryotes and
even a few eukaryotes. And we need a particular
restriction enzyme represented here by a pair of scissors that binds at a certain
sequence of base pairs called a restriction site.
You may remember that enzymes are
usually proteins, and they catalyze or speed up chemical reactions. Well, the reaction that these
enzymes speed up is the breaking of specific bonds on DNA molecules. The restriction enzyme in the
diagram makes the cut represented by the black dashed line, resulting in a staggered
cut that leaves sticky ends, sticky because they can stick back together again, or
to another piece of DNA that’s cut with the same restriction enzyme, because it,
too, will have the same complementary sticky ends.
So what other DNA should we cut
with the same restriction enzyme. So where should we have the
restriction enzyme make these cuts? Here’s a hint. There should be three. We’ll definitely need a cut on
either side of the insulin gene to isolate it from the rest of the DNA that it’s
attached to and another cut on the plasmid to make an opening where the insulin gene
could be inserted. Now the plasmid in the diagram is a
little larger, so we can see how the sticky ends of the insulin gene align with
those of the plasmid forming the complementary base pairs of adenine and thymine and
cytosine and guanine, which are held together by hydrogen bonds.
Before a vector is ready to
transport the gene, it needs to reform the bonds between the sugars and the
phosphates that were broken by the restriction enzymes. And the enzyme needed for this
reaction is gonna be called DNA ligase. And now the plasmid could be moved
into a bacterium using a process called transformation. As bacteria containing the plasmid
reproduce by dividing in two, they also produce copies of the plasmid. Bacteria can be grown in conditions
to promote population growth. And since each bacterium is gonna
be genetically identical to the others, this process is known as cloning. And we’ve reached our goal. We have a population of bacteria
that have the insulin gene, and they could be used to produce the hormone
insulin.
There are other really great
reasons to modify the genes of organisms, like these insulin-producing bacteria. But there are disadvantages as
well. Let’s take a look at some of
these. First, genetically modified
organisms or GMOs have been engineered to contain DNA from another organism, like
bacteria that contain the human insulin gene. We’ve already listed some general
advantages of genetic engineering when we discussed reasons to use this
technology. So we’ll discuss some more specific
advantages of genetically modified organisms here. Microorganisms like bacteria are
relatively cheap to grow, especially compared to animals. They reproduce quickly and can be
engineered to produce hormones, enzymes, antibiotics, or to consume pollutants such
as oil.
Even plants and animals can be
modified to produce disease-fighting proteins like antibodies and antigens that can
be extracted from either their plant tissues or milk or eggs. As the human population grows, but
available farmland does not, genetically modified organisms will be able to help
increase crop yields and nutritional content of certain foods. And this will increase food
security for our future. Plenty of other advantages of GMOs
exist, but let’s turn now to looking at a few of the disadvantages.
Many of the concerns around GMOs
are centered around the fact that we just can’t know all the possible risks. There are a lot of unknowns. Another concern is that antibiotic
resistance genes used in genetically modified bacteria may potentially transfer to
pathogenic or disease-causing bacterial species, making that disease very hard to
treat. All life forms get mutations; even
viruses get mutations and so will GMOs. And that leads to greater
uncertainty in the outcomes. There’s also concern that this
technology will be used to make humans there faster, stronger, and smarter, a whole
new elite class of humans. What will that do to society?
There is concern that people with
the wrong intentions will use this technology for unethical purposes. Many farmers depend on a few huge
corporations to supply them with genetically modified seeds that are patented. And this leads to some concerns
about our food security. There’s a lot more to the ongoing
debate regarding GMOs, but it seems certain that they’re here to stay. And we need to stay informed to
make sure that they’re used wisely. Next up, let’s apply what we’ve
learned to a practice problem.
Which of the following best defines
genetic engineering? (A) Genetic engineering is the
repeated breeding of organisms with desired characteristics. (B) Genetic engineering is the
modification of the DNA of an organism. (C) Genetic engineering is the
modification of the physical characteristics of an organism. (D) Genetic engineering is a form
of cloning. (E) Genetic engineering is the
creation of new animals.
Key knowledge required to answer
this question is a basic understanding of genetic engineering. So let’s take a look at an example
of this technique. Have you ever had to go to the
doctor to get a vaccination and they take out a great big needle? Well, it’s possible that maybe
someday we’ll be getting vaccines from bananas. Vaccines are an important tool to
prevent disease, but they often come with a painful shot. Would you like it if you went to
the doctor and they said, for your vaccination this year, you just have to eat this
banana?
Genetic engineers have been working
on making edible vaccines, and this is the basic gist of what they’re doing. They need to start with something
edible, like a banana, and the pathogen, which is the disease-causing agent. And they have little proteins on
them that our immune system can recognize to attack, and those little proteins are
called antigens. After locating the gene that codes
for the antigen and the genetic material of the pathogen, this gene is isolated from
the rest of the pathogens’ DNA, and it’s inserted into the DNA of the banana. But since bananas are just part of
a banana tree and banana trees have many, many cells that contain DNA, this process
is just performed on a few banana tree cells. Then the cells are cultured and
grown.
Now the bananas will have the
antigen from the pathogen grown in them. And the idea is if you eat enough
of the antigen, your immune system can recognize it and get all ready in case the
real virus or bacterium or other kind of pathogen shows up. So this banana, like all
genetically engineered organisms, contains DNA from more than one kind of
organism. So that’s what genetic engineering
is.
And it’s time to look at our
solution options, starting with (A), genetic engineering is the repeated breeding of
organisms with desired characteristics. But that’s selective breeding and
humans have been doing that for thousands of years. It’s not really considered genetic
engineering. Option (B) says, the genetic
engineering is the modification of the DNA of an organism. And that’s exactly what happened in
our example. So this one sounds really good. Option (C) says, the genetic
engineering is the modification of the physical characteristics of an organism. Well, genetic engineering does
modify physical characteristics of an organism, but not directly. You have to modify the DNA to
result in a change in physical characteristics. So option (C) is not correct.
Option (D) says that genetic
engineering is a form of cloning. Well, cloning is really a part of
the process in genetic engineering. After you have the cell genetically
modified the way you want it, you clone it or make lots of identical cells. So option (D) is not correct. Option (E) says that genetic
engineering is the creation of new animals. But genetic engineering is really
about moving a gene of interest from one species to another species. So option (E) is not correct. Therefore, the answer to the
question, which of the following best defines genetic engineering, is genetic
engineering is the modification of the DNA of an organism.
Here are a few key points from our
lesson on genetic engineering, including a little summary diagram of how to use
restriction enzymes to make blue tomatoes.
