Transcript Gene expression

6D Gene expression
• the process by which
the heritable information in
a gene, the sequence
of DNA base pairs, is made into
a functional gene product, such
as protein or RNA
• http://www.youtube.com/watch?v=OEWOZS_
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Gene expression
• Controls & regulates protein
synthesis (transcription &
translation)
• Remember, every cell is your body
contains the exact same DNA…
…so why does a muscle cell have
different function and structure than a
nerve cell?
• Because some genes are expressed in a
muscle cell that are not expressed in a
nerve cell and vice versa.
• Different genes can also be expressed
in response to environmental factors
or during different stages of an
organism’s life cycle.
Gene expression
• Its like a light
switch…
certain traits
are “turned
on” & “turned
off”
Gene
• Segment of DNA that codes for a trait
• Ex: hair color, eye color
Intron
• any nucleotide sequence within a gene that is
removed by RNA splicing while the final
mature RNA product of a gene is being
generated
Exon
• nucleotide sequence encoded by a gene that
remains present within the final mature RNA
product of that gene after introns have been
removed by RNA splicing.
• This is the expressed genetic material… the
light is turned on.
Gene Expression in Prokaryotic Cells
• Prokaryotic cells such as…
BACTERIA
… contain operons.
Operon
• Groups of genes that are regulated
together.
• “Buddy system”
• Located next to 2 regulatory regions
of DNA – promoter and operator
Promoter
• a region of DNA that initiates transcription of
a particular gene
• promoters are located near the genes they
transcribe
Operator
• a gene that activates the production of
messenger RNA by adjacent structural genes
• When RNA polymerase binds to the promoter,
it is a signal that shows RNA polymerase
where to begin transcription. The operator is
adjacent to the promoter and it controls the
rate of transcription.
Repressor
• A protein called a repressor can bind to the
operator. If the repressor binds to the
operator, the RNA polymerase cannot access
the operon and transcription does not occur.
lac operon
lac operon
• The group do 3 genes (lac Z, lac Y, lacA) MUST
be turned on before the bacterium can use
lactose as food.
• When lactose is not present in the bacterium’s
environment, the repressor binds to the
operator.
• The protein blocks the movement of RNA
polymerase along the DNA, and the operon is
not transcribed into RNA.
• When lactose is present, the repressor binds
to lactose instead opt to the operator. The
path of DNA is cleared from transcription to
occur (like a gate across a road).
Gene Expression in Eukaryotic Cells
Gene Expression in Eukaryotic Cells
• Genes are rarely found in clusters that are
activated by the same promoter. Many
eukaryotic genes are preceded by a short
region of DNA called the TATA box.
TATA box
• Positions RNA polymerase.
Transcription Factors
• DNA-binding proteins that aid in regulating
gene expression.
• Many types of transcription factors. Each type
•Ex: opening
packed chromatin
(enhancing transcription)
affects
genetightly
expression
in different
ways.
• Ex: opening tightly packed chromatin
(enhancing transcription)
Types of Transcription Factors
• opening tightly packed chromatin (enhancing
transcription)
• Attracting RNA polymerase
• Blocking access to certain genes
• http://www.youtube.com/watch?v=T9Wszg7F
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http://www.youtube.com/watch?v=2sMFswbO
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http://phet.colorado.edu/en/simulation/geneexpression-basics
http://phet.colorado.edu/en/simulation/genemachine-lac-operon