Download Mendelian Genetics

Gene Regulation and Genomics
Differentiation
• As development progresses,
cells becomes more
specialized and restricted in
the expression of their genetic
content. This leads to many
types of cells in a complex
organism.
• However, differentiated cell
may retain all their genetic
potential.
• Salamanders can regenerate
a lost limb.
• Tissue culture has allowed
many plants to beproduced
from a single plant.
Plant Tissue Culture
• This is BIG business, and is very important in the horticultural
industry.
• Thirty years ago if an orchid breeder had a spectacular plant it
might produce two or three asexual off-shoots per year. Each of
these could be sold for, perhaps, $150-200. Sounds good?
• Today that same plant can be placed in tissue culture and the
grower can produce 20,000 identical plants, sell them for $10 each.
• $200,000 vs. $300-400?? You choose.
• The center for plant tissue culture in Florida is the area around
Apopka.
• The process is simple in theory, but more complicated in practice.
What growth medium is required?; What part of the plant yields the
best cells for tissue culture?; At what rate and how long are cells
shaken in solution? Etc.
There’s a lot of information in that cell! How
can we regulate its use?
• In eukaryotes the cells genes are located on
chromosomes.
• A chromosome consists of DNA and histones. Histone
proteins are a framework around which the DNA can be
tightly coiled. The term for the bead-like DNA-histone
complex that can be seen in electron micrographs is
termed a nucleosome.
• The tight packing of the DNA in the chromosome helps
to regulate gene expression by preventing transcription
proteins from contacting the DNA. Only when portions
of the DNA uncoil can transcription of information occur.
Alternative RNA splicing
• Remember: the DNA
message that is copied
contain both introns and
exons.
• The introns are removed to
produce a functional mRNA.
• If splicing occurs in different
ways, different mRNAs are
produced and their products
will also be different.
• This means that alternative
RNA splicing can allow a gene
to code for several different
peptide chains, depending
upon how the information is
spliced together.
A Cell is not a Simple Strucuture!
• After mRNA is produced other events will happen.
– mRNA must be broken down. When this happens is regulated
by the cell.
– When translation actually occurs can be controlled by the cell.
– The peptide that is formed during translation may need to be
bent, folded, or chemically altered before it becomes functional.
– Proteins may be destroyed by the cell after a set period of time.
– These mechanisms enable the cell to control the amount and
the type of protein that is active in the cell at any given point in
time.
Reproductive Cloning
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Reproductive cloning adds a nucleus from a donor cell to an egg cell, whose
nucleus has bee removed.
The result is a new animal exactly like the parent (i.e. Dolly , the sheep)
The technique is not without problems , and its usefulness is still to be
proven.
There are great ethical concerns about human cloning, and most
researchers are strongly opposed to it. (Would you really want another you,
and would you be you if you did get cloned??) That’s a lot of you!
Therapeutic cloning
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Unlike reproductive cloning,
therapeutic cloning has great
medical potential.
In this procedure stem cells
(adult and/or embryonic) are
cultured in the lab, and then
induced to transform into
specialized tissues.
The use of embryonic stem cells
has much promise, but much of
this has been lost in the current
moral and ethical debates.
If one is truly opposed to
embryonic stem cell research,
one should also be ethically
boound to forgo the use of any
therapies or cures that result
from it.
Signal Transduction Pathway
• How do cell know when to differentiate?
• How are cellular activities regulated within an organism?
• The processes is relatively straightforward:
– A signal molecule, produced elsewhere, attaches to a
receptor protein on the cell membrane.
– This causes a cascade of reactions between relay
proteins in the cell’s interior.
– The last relay molecule activates a transcription
factor that causes the transcription of a specific gene
in the DNA of the nucleus.
– This leads to the production of a protein that may act
as an enzyme or structural element needed to effect
a change in the cell.
Oncogenes
• Oncogenes are cancer causing genes, and usually
trigger increased production of cell growth factors.
• Active oncogenes, along with defective tumor-supressor
genes, can lead to the development of cancerous
tumors.
• Usually cancer is the result of multiple mutations in a
somatic cell.
• Many cells probably develop these mutations, but are
detected by cells of the immune system and eliminated
before that can give rise to a tumor.
• The next slides has two illustrations of steps in tumor
development.
Tumor suppressor gene
• If a gene that inhibits cell division is defective, it can lead to the
uncontrolled replication of cells and the development of a tumor.
• This is seen in the illustration below.
Carcinogens
• Many factors can cause DNA mutations that lead to
tumor development. These factors are called
carcinogens.
• Carcinogens can be physical factors, such as, X-rays,
UV radiation, and radiation from radon (naturally
occurring) or nuclear weapons (man-made).
• They can be chemical factors, like the chemicals in
tobacco, or cleaning agents, such as benzene.
• Even some viruses can lead to cancer. Cervical cancer
is one example. This is the reason for the development
of a vaccine against sexually transmitted viruses.
• Avoidance of risk factors is one way to decrease the
chance of developing cancer.
Genomics, the study of whole sets of genes
• DNA technology has lead to the development of the field
of genomic research. This research has many potential
applications in the areas of medicine, agriculture,
forensic science, and production of products for
industrial and pharmacological uses.
• With the development of these lines of research, a host
of legal, ethical, social, and environmental issues have
arisen. It may take years, if not decades, to resolve
many of the concerns that individuals are voicing today.
• None the less, DNA technology and genomics is one of
the most exciting areas of modern biology.
Recombinant DNA Technology
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Plasmids are circular DNA molecules found in bacteria which can be
used to insert genes into bacterial cells.
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The genes that are inserted can come from many sources other than
bacteria.
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This technology has allowed the insertion of genes into bacteria, which
can then be grown in great quantity, yield large amounts of the product
for which that gene codes.
•
This procedure can also yield large quantities of cells that carry gene
that chaanges something aboutr the cell in which it is found.
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A diagram of this process can be seen in the next slide.
Using plasmids to copy genes and make proteins
Restriction enzymes
• To get a piece of DNA
containing the gene to be
studied, the DNA is cut into
pieces using restriction
enzymes.
• These enzymes recognize
short segments of DNA and
cut the DNA at those points.
• Because the cuts are
staggered, there are
unattached bases at the ends
(sticky ends)
• New DNA pieces can attach to
the sticky ends, and then DNA
ligase covalently bonds the
pieces together.
• The process of inserting
and cloning a gene can
be seen in the illustration
to the right.
• Note that once the plastid
has a gene inserted into
its DNA, and the plastid
is put into a bacterium,
tremendous numbers of
bacteria containing the
gene can be produced in
a short period of time.
How to make a clean gene!
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Remember, when you copy a DNA
gene it consists of introns and
exons. You need to remove the
introns to get a ‘clean’ piece of
mRNA.
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To get a gene to clone, one must
isolate the ‘clean’ mRNA, and then
use reverse transcriptase to
make a DNA copy of the mRNA.
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After the RNA is removed, a
complementary stand of DNA is
formed. The result is doublestranded cDNA.
Uses of Recombinant DNA Technology
• Both bacterial cells and mammalian cells have been used to
generate useful products. Mammalian cells can be genetically
engineered so that the desired protein is secreted in the animal’s
milk. The product can then be isolated from the milk and used.
Gel Electrophoresis
• One technique for studying DNA uses a thin gel to separate DNA
based on size and electrical charge. A DNA sample is introduced
into a well in the gel, and a high voltage current causes the
molecule to migrate through the gel. The finished gels can be
stained and photographed. Samples can be compared using the
migration patterns that are present.
DNA Fingerprints
• The use of DNA evidence in
forensic science has become
very widespread.
• The chance of two
individuals having the same
DNA pattern is extremely
small if enough markers are
used.
• DNA matches have enabled
the identification of the
victims of tragedies such as,
plane crashes, 9-11, ethnic
cleansing.
• Innocent persons on death
row have been freed due to
DNA evidence which proved
their innocence.
Gene Therapy
• There has been much hope
for effective gene therapy. It
could allow the body to
compensate for genes that
are defective or nonfunctional.
• At present success has been
very limited, and some clinical
trials have been discontinued
due to unforeseen problems.
• Will gene therapy place a
significant role in the future of
medicine? Only time will tell.
Polymerase Chain Reaction (PCR)
• This technique has allowed
researchers to take a minute
amount of DNA and, from it,
produce a large quantity of DNA
for analysis.
• Using a series of enzymes and
cycles of heating and cooling,
new copies of DNA are created.
A complete cycle only takes a
few minutes, therefore in a few
hours the number of DNA
molecules produced is
tremendous. (calculate how
many you would have after 20
cycles)
Human Genome Project
• No one in today’s world should leave a basic biology course and
not be aware of the Human Genome Project, its purpose and its
potential for mankind.
• Purpose: map out the entire nucleotide sequence of the DNA of
the human chromosome.
• This was completed years ahead of schedule due to the rapid
development of techniques in sequencing.
• Potential: insight into human development; insight into
evolutionary relationships; and .
• better diagnosis and treatment of many of our commonest and
most debilitating diseases.
• Go to the links provided in this lesson to explore the Human
Genome Project and the whole field of genomics.
Pros and Cons of Genetically Modified
Organisms
• Since the advent of the first genetically modified crops, questions
of environmental impact and risks to health have surfaced
repeatedly.
• The EU (European Union) has a very strong bias against GM
crops. There is the concern that transgenic crops could endanger
individuals with food allergies. You could consume a food not
knowing that it contained an allergen that could trigger a severe
and dangerous reaction.
• China has made wide use of GM crops. If you need to feed
1,300,000,000 people, high yield may be more important than the
slight chance of mortality due to food allergy.
• There are many other concerns and benefits that we as a society
will have to carefully weight as we move into this uncharted era
GM plants and animals.
This represents the information known to be located on chromosomes #9 and
#4. The graphics are courtesy of the U.S. Dept. of Energy, Genome
Management Information System of the Oak Ridge National Lab