Transcript group_presentation

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Trinucleotide Repeats
by: Guy, Hannah, Julien
and Max
Trinucleotide Repeats
•Within our DNA, it is very common to have a
triplet base repeat in which the same triplets are
repeated more than once in a strand.
•If the number of repeats is too large, it can trigger
a problem that results QuickTime™
in an identifiable
disease.
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•If the repeat is present
intoasee
gene,
an expansion of
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the repeat results in a defective gene product and
often disease.
•Many inherited diseases are the result of a
single difference in the genetic code for a
particular protein. As a result of that
difference, either a protein is not made at all,
made in inadequate amounts, or made in a
defective form.
Trinucleotide Repeats Continued
• The most common repeat is CAG which codes for
Glutamine. 8 of the 14 trinucleotide repeat
diseases possess this repeat and are called
polyglutamine, and the other 6 who don’t have this
repeat, are called non- polyglutamine.
• Trinucleotide repeat disorders generally show
genetic anticipation, where their severity increases
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with each successive generation
that
inherits
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• Trinucleotide repeat disorders are the result of
extensive duplication of a single codon. In fact, the
cause is trinucleotide expansion up to a repeat
number above a certain threshold level.
• Expansion of trinucleotide repeats is now
recognized as a major cause of neurological
disease.
HUNTINGTONS DISEASE
•
•
•
1 out of the 14 documented
trinucleotide repeat disorders;
1 of several polyglutamine
diseases
The trinucleotide repeat in
Huntington’s disease is the
CAG repeat. Patients with the
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CAG repeat in the Huntingtin
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gene who have Huntington’s
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disease have repeat lengths
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between 39-70 repeats. A
normal chromosome only has
9 to 30 CAG's.
This repetition produces an
altered form of the Htt protein,
mutant Huntingtin which
results in neuronal cell death
in select areas of the brain
and is a terminal illness.
HUNTINGTONS CONT.
• Since the Huntingtin protein is found in most neurons throughout
the brain, these neurons become infected and start a process of
cell death. Once enough cells die within the brain, Huntington’s
disease occurs.
• Symptoms: Loss of facial expression (called "masks in
movement") or exaggerated facial gestures, ability to sit or stand
stably, speech, chewing and swallowing. Eventually, it leads to
an inability to walk, talk and eat. Death occurs generally 10- 30
years after the first sign of symptoms.
• Prevalence:1 in every 10,000 Americans have Huntington’s
disease, with about 150,000 at risk of inheriting it from a parent.
• Currently, there is no cure, but symptoms are managed by using
medications.
Myotonic Dystrophy
Myotonic Dystrophy is a severe
inherent form of muscular
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decomposition of the muscle
occurs. This is often
characterized by mental
retardation or the difficulty of
movement of limbs.
GENE SILENCING
Discovered
• Gene silencing is the method used to “silence” or
block out of specific sequences of DNA or RNA,
used to help prevent or treat diseases and also
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• In 2003 Andy are
Fire
of the Carnegie Institute of
Washington and Craig Mello of the University of
Massachusetts realized they could prevent a gene
from being expressed by injecting or feeding the
animal (nematode worms in this case) a double
stranded RNA that corresponds to the worm’s DNA
gene they are trying to silence
GENE SILENCING
Process 4 Steps
• Step 1: scientist insert a double-stranded RNA into a cell, one of
the strands of that RNA contains the identical sequence of
bases to the gene that the scientist wants to silence (for now we
will call it code X)
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• Step 2: because are
cells
should
only
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cell identifies the double-stranded RNA as an intruder
CELL
Double stranded RNA
Identical to desired sequence
GENE SILENCING
Process Cont.
• Step 3: it is the Dicer enzyme’s job to get rid of this intruder RNA
strand and then goes after the double-stranded RNA, however,
when it does this, because one of the stands in the doublestranded RNA codes for the gene that is desired to be silent
(code X), and there is an
identicaland
code
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the cell’s original
(also code
X), the Dicer enzyme
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recognizes both code
Xs as
intruders
and destroys the doublestranded RNA along with the code X portion of the cell’s original
mRNA
• Step 4: because the Dice enzyme destroyed the code X in the
cell’s mRNA code X will no longer be translated through protein
synthesis and will not code to make the undesired protein, and
therefore it will never be expressed
FRIEDREICHS ATAXIA
• It is an inherited disease that causes damage to your nervous system that can later
cause speech problems or heart disease.
• Can result in the loss of nerve tissue in the spinal cord. The spinal cord will become
thinner and cause you to be clumsy and have little balance.
• Can also result in the loss of nerves that control the movement of your arms and
legs.
• Friedreich’s Ataxia is an autosomal recessive disease caused by the mutation in gene
X25.
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• Some symptoms
include:
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– o Muscle
– o Loss of coordination
– o Hearing loss
– o Slurred speech
– o Scoliosis
– o Extreme heart conditions
• Some people suffering from Friedreich’s Ataxia may require surgery, mainly for the
heart and spinal cord. For the spinal cord, a metal rod may be places in the spine to
prevent scoliosis.
• Researchers are expecting a drug to come out for Friedreich’s Ataxia around spring
2008.