Download Chapter 26: Biotechnology

Chapter 26: Biotechnology
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26-1
Cloning of a Gene
Cloning is the production of identical
copies through asexual means.
Cloning occurs naturally in new plant
shoots, bacterial colonies, and identical
human twins.
Gene cloning is the production of many
identical copies of a gene.
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Recombinant DNA Technology
Recombinant DNA (rDNA) contains DNA
from two or more different sources.
To make rDNA, a technician needs a
vector by which rDNA will be
introduced into the host cell.
A plasmid (a small accessory ring of DNA
in bacteria) or virus can be used as a
vector to insert foreign DNA into a host
cell.
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Cloning a human gene
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Restriction enzymes cleave the vector
DNA and the source DNA at a specific
sequence, leaving “sticky” ends, that
allow a portion of source DNA to be
inserted into the vector DNA.
DNA ligase then seals the openings and
recombinant DNA is formed.
Bacterial cells take up recombinant
plasmids and clone the new DNA.
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When a viral vector is used the cloned
DNA is inside newly formed
bacteriophages.
To express a human gene in a bacterium
it must not have introns.
Reverse transcriptase can be used to
make a DNA copy of mRNA; this
complementary DNA does not contain
introns.
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The Polymerase Chain Reaction
The polymerase chain reaction (PCR)
produces many copies of a single gene
or piece of DNA.
PCR requires DNA polymerase and a
supply of nucleotides for the new DNA
strands.
PCR is a chain reaction because the
targeted DNA is repeatedly replicated
as long as the process continues.
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Polymerase chain reaction (PCR)
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Analyzing DNA Segments
The entire genome of an individual can
be cut by restriction enzymes to yield
variable fragment lengths.
Gel electrophoresis separates fragment
lengths and the use of probes results in
a pattern unique to the individual,
sometimes called a DNA fingerprint.
A DNA fingerprint resembles that of one’s
parents because it is inherited.
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It is possible identify a person who has
committed a crime, identify a cancer
gene, or tell who is related to whom by
performing a DNA fingerprint.
Since PCR can amplify the smallest
amount of DNA, a single sperm, or one
cell on a toothbrush, provides enough
DNA to be identified by comparison
with sample DNA.
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Biotechnology Products
Today, bacteria, plants, and animals are
genetically engineered to make
biotechnology products.
Organisms that have had a foreign gene
inserted into them are called transgenic
organisms.
There are now transgenic bacteria,
transgenic plants, and transgenic
animals.
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Transgenic Bacteria
Recombinant DNA technology is used to
produced transgenic bacteria, which are
grown in huge vats called bioreactors.
Transgenic bacteria are used to produce:
insulin, human growth hormone, tissue
plasminogen activator, and hepatitis B
vaccine.
They also add insecticidal toxins to plants,
reduce frost damage on plants, degrade
wastes, produce chemicals, and help
mine metals.
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Biotechnology products
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Transgenic Plants
Foreign genes are added to protoplasts
using an electric current.
Foreign genes in cotton, corn, and
potatoes have given them pest
resistance; soybeans are made resistant
to herbicide for no-till farming.
Transgenic plants produce human
hormones, clotting factors, and
antibodies in their seeds; one weed has
even been engineered to produce plastic
granules.
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Transgenic Animals
Foreign genes can be inserted into
animal eggs by hand or by vortex
mixing.
Gene pharming uses transgenic farm
animals to produce pharmaceuticals in
their milk.
Animals may produce drugs for the
treatment of cystic fibrosis, cancer, and
blood diseases.
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Transgenic animals
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Cloning Transgenic Animals
Cloning of mammals was once
considered impossible, but has now
been accomplished with sheep, calves
and goats.
A 2n nucleus from a bioengineered
animal is inserted into enucleated eggs
from a donor.
A surrogate mother gives birth to the
cloned animals.
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Animal Organs as Biotechnology
Products
Scientists are genetically engineering
pigs to serve as organ donors for
humans who need transplants.
Transplants of organs across species is
called xenotransplantation.
Researchers are trying to make organs
less antigenic to humans.
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One concern is whether pig organs
might carry animal viruses into
humans; HIV is a virus that jumped
from monkeys into humans.
Tissue engineering is an alternative
method of securing bioartificial organs
– transplant material from culturing
human tissue from a mixture of cells
and synthetic polymers.
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The Human Genome Project
The Human Genome Project has two
goals:
(1) to construct a map that shows the
sequence of bases on all the human
chromosomes and
(2) to construct a map that shows the
sequence of genes along all the
human chromosomes.
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The Base Sequence Map
The first goal has been completed and
researchers know the sequence of
three billion base pairs after 15 years of
research.
The two agencies that completed the task
are The International Human Genome
Sequencing Consortium and Celera
Genomics, a private company.
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DNA sequences are similar among
organisms and the differences may be
due to regulation of genes.
It has also been determined that humans
share a large number of genes with
very simple organisms such as
bacteria.
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The Genetic Map
Much research must be done to locate
the genes on each human
chromosome.
The number of protein-encoding genes
appears to be very low, about 30,000.
Some believe each gene could code for
three different proteins by using
different combinations of exons.
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Genetic map of chromosome 17
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A gene map could help discover mutant
genes and lead to the development of
medicines to treat these disorders.
Germline therapy, that is done before a
child is born, may eventually be
possible.
Many ethical questions surround how
human genome maps should be used.
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Gene Therapy
Gene therapy is the insertion of genetic
material into human cells for the
treatment of a disorder.
A patient would be given healthy genes
to make up for any faulty genes.
Gene therapy includes ex vivo (outside
the body) and in vivo (inside the body)
methods.
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Ex Vivo Gene Therapy
Using the ex vivo method, bone marrow
stem cells are withdrawn from the
body, a retrovirus is used to insert a
normal gene into them, and the stem
cells are returned to the body.
This method of gene therapy works for
severe combined immunodeficiency
(SCID) and may work for familial
hypercholesterolemia where liver cells
lack a receptor for removing blood
cholesterol.
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Ex vivo gene therapy in humans
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In Vivo Gene Therapy
Cystic fibrosis patients lack a gene that
codes for a membrane carrier of
chloride ions; researchers try to deliver
the gene by nose sprays containing
adenoviruses or liposomes.
A gene that codes for new blood vessel
growth is being injected to stimulate
new coronary blood vessels.
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Many researchers are trying to cure
cancer by inserting genes to make
healthy cells tolerant of chemotherapy
or use gene p53 to bring about
apoptosis of cancer cells.
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Chapter Summary
Recombinant DNA technology utilizes
genetically altered bacteria and viruses
to clone a gene.
The polymerase chain reaction (PCR)
rapidly makes copies of DNA
segments; this allows detailed analysis
of the DNA for a wide range of uses.
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Transgenic bacteria, agricultural plants,
and farm animals have been genetically
engineered to produce commercially
valuable products and applications.
Agricultural plants and farm animals
have been genetically engineered to
improve their yield.
Farm animals have been genetically
engineered to serve as a source of
organs for human transplant patients.
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It is now possible to clone animals;
cloning is used to produce multiple
copies of farm animals that have been
genetically engineered.
The Human Genome Project aims to
sequence the DNA bases of each
chromosome and to map the genes on
each chromosome; the first goal is
completed.
Gene therapy is now being used to replace
defective genes with healthy genes and
to help cure various human ills.
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