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13.2 Recombinant DNA Technology
◗ Before You Read
SC.H.3.4.2 The student knows that technological problems often create a demand for new
scientific knowledge and that new technologies make it possible for scientists to extend
their research in a way that advances science. Also covers SC.H.3.4.3, SC.H.3.4.5, SC.H.3.4.6
This section discusses the technology that allows scientists to combine the DNA of one organism
with the DNA of another organism. The result can be organisms with new characteristics. What
would you think of a plant that glows like a firefly or a cotton crop that produces its own insecticide?
On the lines below, list some examples of useful changes to an organism that you would like to see
made through DNA technology.
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◗ Read to Learn
Identify
Details Highlight each key
term introduced in this section. Say the key term aloud.
Then, highlight the sentence
that explains the key term.
1. What advantages does
genetic engineering have
over selective breeding?
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Chapter 13
In the previous section you learned that selective breeding
increases the frequency of desired traits, or alleles, in a population. You also learned that selective breeding techniques such as
inbreeding and creating hybrids take time. In many cases the
offspring have to mature before the traits become obvious. Sometimes it takes several generations before the desired trait becomes
common in the population.
There is a faster and more reliable way to increase the frequency
of a desired allele in a population. It is called genetic engineering.
In genetic engineering, very small pieces or fragments of DNA
are cut from one organism and placed inside another organism.
When DNA is made by connecting, or recombining, fragments
of DNA from different sources, it is called recombinant
(ree KAHM buh nunt) DNA.
An organism uses the recombinant DNA as if it were its own.
The DNA of two different species can even be combined. For
example, inserting a specific part of the DNA of a firefly into the
DNA of a plant will cause the plant to glow. When an organism
contains recombinant DNA from a different species, it is called
a transgenic organism. The glowing plant is an example of a
transgenic organism.
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Genetic Engineering
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13.2
Recombinant DNA Technology, continued
What is the process for producing a
transgenic organism?
Producing a transgenic organism is a three-step process. The
first step is to cut the DNA fragment out of one organism. The
second step is to connect the DNA fragment to a carrier. The third
step is to insert the DNA fragment and its carrier into a new
organism. Let’s take a closer look at each step.
How is a DNA fragment cut from an organism?
Scientists have discovered that there are proteins called restriction enzymes that cut DNA. They are bacterial proteins that can
cut both strands of the DNA molecule at a specific nucleotide
sequence. There are hundreds of different restriction enzymes.
Each one cuts DNA in a different place. In our example, Step 1
is picking a restriction enzyme that cuts the firefly DNA strand
at the sequence that codes for making the enzyme that lights up
the firefly.
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
How are DNA fragments connected to a carrier?
Organisms do not easily accept loose fragments of DNA from
other organisms. For this reason, the DNA fragment needs a carrier to take it into the host cell. This is Step 2. In our example,
the firefly DNA gets inserted into the carrier or vector DNA.
A vector is the means by which DNA from another species can
be carried into a host cell.
Biological vectors include viruses and plasmids. A plasmid is a
small ring of DNA found in a bacterial cell. The genes of a plasmid are different from those on the bacterial chromosome. In our
example, the firefly DNA strand was inserted into a plasmid in a
bacterial cell in Step 2. Now, in Step 3, the plasmid vector is
inserted into a plant.
2. What is a vector?
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What are clones?
With the firefly DNA now a part of it, the plasmid reproduces
within the bacterial cell, making up to 500 copies of itself. Every
time the host cell divides, it copies the recombinant DNA as it
copies its own DNA. Such genetically identical copies are called
clones. Each identical recombinant DNA molecule is called a
gene clone. Because the bacterial host cells in the plant will continue to copy the recombinant DNA, the plant will always have
the firefly’s DNA—and its light—within it.
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Chapter 13
145
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13.2
Recombinant DNA Technology, continued
In some experiments, scientists insert particular types
Recombinant DNA
Bacterial
of recombinant DNA into
Recombined
chromosome
plasmid
host cells. This DNA has
code within it to make a
certain type of protein.
E. coli
Scientists then study what
Plasmid
this protein does in cells that
Human
do not ordinarily produce it.
growth
hormone
At other times, scientists produce mutant forms of a protein. They then study how the
mutation affects the function
of the protein within a cell.
Technology has made gene cloning fairly simple. Scientists
have built upon gene cloning to clone an entire animal. The most
3. Why do scientists want to
famous cloned animal was Dolly the sheep, cloned in 1997. The
clone animals?
cloning process is not efficient, but scientists hope someday to use
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it so that ranchers and farmers can clone the most productive,
healthy animals to increase and improve the food supply.
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Scientists developed a method of replicating DNA outside of
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living organisms, called polymerase chain reaction (PCR). This
method uses heat to separate DNA strands from each other. An
enzyme from a heat-loving bacterium is used to replicate the
DNA when the correct nucleotides are added to a PCR machine.
The PCR machine can make millions of copies of DNA in a day.
Scientists analyze bacterial, plant, animal, and human DNA.
Scientists use this type of DNA analysis in crime investigations and
in the diagnosis of disease. Scientists also use PCR to provide pure
DNA that is used to determine the correct sequence of DNA
bases. This information helps scientists identify mutations.
4. Which three areas will
most likely benefit from
DNA technology?
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Applications of DNA Technology
How can humans benefit from DNA technology? Three main
areas seem to offer the greatest promise: industry, medicine, and
agriculture. For example, scientists have changed the E. coli bacteria to produce the expensive blue dye used to color denim blue
jeans. Scientists are also trying to develop corn that contains as
much protein as beef.
In medicine, recombinant DNA is used to produce insulin and
the human growth hormone. The human gene responsible for
clotting blood has been inserted into sheep chromosomes. The
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Foreign DNA
(gene for human
Cleavage sites growth hormone)
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13.2
Recombinant DNA Technology, continued
sheep produce the clotting protein, which is then used for patients
with hemophilia, a disease in which blood cannot clot quickly.
Researchers are discovering ways to increase the amount of
vitamins in certain crops. That will help provide better nutrition.
Some plants have already been developed that produce toxins to
make them resistant to insects. That will limit the use of dangerous pesticides.
◗ After You Read
Mini Glossary
clone: genetically identical copy of an organism
or gene
genetic engineering: method of cutting DNA
from one organism and inserting the
DNA fragment into a host organism of the
same or different species
plasmid: small ring of DNA found in a bacterial
cell that is used as a biological vector
restriction enzyme: DNA-cutting enzyme that
can cut both strands of a DNA molecule at a
specific nucleotide sequence
transgenic organism: organism that contains
recombinant DNA from a different species
vector: means by which DNA from another
species can be carried into the host cell; may
be biological or mechanical
Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
recombinant (ree KAHM buh nunt) DNA:
DNA made by recombining fragments
of DNA from different sources
1. Read the terms and their definitions in the Mini Glossary above. Circle two terms that are
related to one another. On the lines below, tell how these terms are related.
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2. In the boxes below, list the steps for producing a transgenic organism.
Recombinant DNA Process for Producing a Transgenic Organism
Step 1
Step 2
Step 3
Visit the Glencoe Science Web site at science.glencoe.com to find
your biology book and learn more about recombinant DNA technology.
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Chapter 13
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