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Explain how scientists manipulate DNA.
Describe the importance of recombinant DNA.
Define transgenic and describe the usefulness of
some transgenic organisms to humans.
Lesson Summary
Copying DNA
 Genetic engineers can transfer a gene from one organism to another to
achieve a goal, but first, individual genes must be identified and
separated from DNA. The original method (used by Douglas Prasher)
involved several steps:
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Determine the amino acid sequence in a protein.
Predict the mRNA code for that sequence.
Use a complementary base sequence to attract the predicted mRNA.
Find the DNA fragment that binds to the mRNA.
 Once scientists find a gene, they can use a technique called the
polymerase chain reaction to make many copies.
1.
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Heat separates the DNA into two strands.
As the DNA cools, primers are added to opposite ends of the strands.
DNA polymerase adds nucleotides between the primers, producing
two complementary strands. The process can be repeated as many
times as needed.
Lesson Overview
Recombinant DNA
Polymerase Chain Reaction
Once biologists find a gene, a
technique known as
polymerase chain reaction
(PCR) allows them to make
many copies of it.
1. A piece of DNA is heated, which
separates its two strands.
Lesson Overview
Recombinant DNA
Polymerase Chain Reaction
2. At each end of the original piece
of DNA, a biologist adds a short
piece of DNA that complements a
portion of the sequence.
These short pieces are known as
primers because they prepare, or
prime, a place for DNA
polymerase to start working.
Lesson Overview
Recombinant DNA
Polymerase Chain Reaction
3. DNA polymerase copies the
region between the primers.
These copies then serve as
templates to make more copies.
4. In this way, just a few dozen
cycles of replication can produce
billions of copies of the DNA
between the primers.
Lesson Summary
Changing DNA
 Recombinant DNA molecules contain DNA from two
different sources. Recombinant-DNA technology can
change the genetic composition of living organisms.
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Plasmids are circular DNA molecules found in
bacteria and yeasts; they are widely used by scientists
studying recombinant DNA, because DNA joined to a
plasmid can be replicated.
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A genetic marker is a gene that is used to
differentiate a cell that carries a recombinant plasmid
from those that do not.
Lesson Overview
Recombinant DNA
Plasmids and Genetic Markers
In addition to their own large
chromosomes, some bacteria
contain small circular DNA
molecules known as plasmids.
Joining DNA to a plasmid, and
then using the recombinant
plasmid to transform bacteria,
results in the replication of the
newly added DNA along with the
rest of the cell’s genome.
Lesson Overview
Recombinant DNA
Plasmid DNA Transformation Using
Human Growth Hormone
Lesson Overview
Recombinant DNA
Plasmids and Genetic Markers
The new combination of genes is then returned to a bacterial cell, which
replicates the recombinant DNA over and over again and produces
human growth hormone.
Lesson Overview
Recombinant DNA
Plasmids and Genetic Markers
The recombinant plasmid has a
genetic marker, such as a gene for
antibiotic resistance. A genetic
marker is a gene that makes it
possible to distinguish bacteria that
carry the plasmid from those that
don’t.
This plasmid contains the antibiotic
resistance genes tetr and ampr.
After transformation, the bacteria
culture is treated with an antibiotic.
Only those cells that have been
transformed survive, because only
they carry the resistance gene.
Lesson Overview
Recombinant DNA
Recombinant DNA & Gene Splicing (6:15)
Lesson Summary
 Transgenic Organisms
 Transgenic organisms contain genes from other
species. They result from the insertion of recombinant
DNA into the genome of the host organism.
 A clone is a member of a population of genetically
identical cells.
Lesson Overview
Recombinant DNA
Transgenic Organisms
The universal nature of the genetic code makes it possible to construct
organisms that are transgenic, containing genes from other species.
Like bacterial plasmids, the DNA molecules used for transformation of
plant and animal cells contain genetic markers that help scientists identify
which cells have been transformed.
Lesson Overview
Recombinant DNA
Transgenic Organisms
Transgenic technology was perfected using mice in the 1980s.
Genetic engineers can now produce transgenic plants, animals, and
microorganisms.
By examining the traits of a genetically modified organism, it is possible to
learn about the function of the transferred gene.
Lesson Overview
Recombinant DNA
Transgenic Plants: Transforming a Plant
with Agrobacterium
Lesson Overview
Recombinant DNA
Transgenic Plants
There are other ways to produce transgenic plants as well.
When their cell walls are removed, plant cells in culture will sometimes
take up DNA on their own.
DNA can also be injected directly into some cells.
If transformation is successful, the recombinant DNA is integrated into
one of the plant cell’s chromosomes.
Lesson Overview
Recombinant DNA
Transgenic Animals
Scientists can transform animal cells using some of the same
techniques used for plant cells.
The egg cells of many animals are large enough that DNA can be
injected directly into the nucleus.
Once the DNA is in the nucleus, enzymes that are normally responsible
for DNA repair and recombination may help insert the foreign DNA into
the chromosomes of the injected cell.
Why do this?
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Transgenic animals can help create new medicines & produce valuable products.
One of the first uses of transgenesis was to make the E. Coli bacteria produce human insulin, which could then be
gathered cheaply, rather than having to be harvested from more expensive animals like pigs.
A more contemporary example can be seen in the use of transgenic goats to product an anticoagulant in their milk.
Mice can be modified so that researchers can observe specific responses their tissue has to diseases. This can lead
to the development of drugs and treatments for humans suffering from those diseases
People with sickle cell anemia can benefit from transgenic animals that contribute to gene therapy.
A transgenic pig has been produced with the ability to synthesize human hemoglobin for use as a blood substitute.
A transgenic cow has been bred with the ability to produce human lactoferrin, an iron-building milk protein and a
potential antibacterial agent.
A transgenic sheep can synthesize a protein that helps emphysema patients breathe more easily
A transgenic goat has been developed to produce a protein needed by cystic fibrosis patients.
GloFish®. These are zebrafish that have been modified to include genes that make them glow fluorescent colors.
The fish were created in 1999 with the goal of helping to detect pollutants, but it quickly became apparent that
they had huge potential as a novelty item. They come in three colors, with green GloFish® derived from the GFP
protein from jellyfish, a red GloFish® derived from a type of sea coral, and a yellow GloFish® derived from a variant
of the jellyfish protein.
http://www.transgenicanimals.info/pros-and-cons-of-transgenic-animals/
http://www.cliffsnotes.com/sciences/biology/biology/recombinant-dna-andbiotechnology/transgenic-animals
http://www.wisegeek.com/what-are-transgenic-animals.htm
Lesson Overview
Recombinant DNA
Transgenic Animals
Recently it has become possible to eliminate particular genes by
constructing DNA molecules with two ends that will sometimes
recombine with specific sequences in the host chromosome.
Once they recombine, the host gene normally found between those
two sequences may be lost or specifically replaced with a new gene.
This kind of gene replacement has made it possible to pinpoint the
specific functions of genes in many organisms, including mice.
Lesson Overview
Recombinant DNA
Cloning
A clone is a member of a population of genetically identical cells
produced from a single cell
The technique of cloning uses a single cell from an adult organism to
grow an entirely new individual that is genetically identical to the
organism from which the cell was taken.
Clones of animals were first produced in 1952 using amphibian
tadpoles.
In 1997, Scottish scientist Ian Wilmut announced that he had
produced a sheep, called Dolly, by cloning.
Lesson Overview
Recombinant DNA
Cloning Animals—Nuclear
Transplantation