Transcript Gene Expression and Cell Differentiation

Gene Expression and Cell
Differentiation
There are hundreds of different
types of cells in your body, and
each type has a unique function.
We’re going to compare a few
different types of cells to see how
much they have in common.
Your Best Guess
For each pair of cells in your body,
you are going to predict what
percentage of DNA is the same in
the two types of cells.
What percentage of the DNA is the
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same in your blood cells and nerve cells?
What percentage of the DNA is the
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same in your rods (eye) and lung cells?
What percentage of the DNA is the
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same in your liver and bone cells?
What percentage of the DNA is the
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same in your blood cells and nerve cells?
Answer: 100%
What percentage of the DNA is the
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same in your rods (eye) and lung cells?
Answer: 100%
What percentage of the DNA is the
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same in your liver and bone cells?
Answer: 100%
Hmmm…
How can these cells that have
very different functions have
the exact same DNA in the
nucleus?
Hmmm…
How does the body use the
exact same set of instructions to
make such different structures?
• http://www.dnatube.com/video/2933/The-HumanGenome-Project-Video--3D-Animation-Introduction
• http://www.dnalc.org/resources/3d/10-tripletcode.html
• http://www.dnalc.org/resources/3d/09-how-much-dnacodes-for-protein.html
Gene Expression
• The explanation for how many different cell types
are made from the exact same DNA lies in how
the genes are expressed in each cell type.
• The gene to make a certain protein is turned on
in some cells and turned off in others.
• All cells have all the instructions in their DNA to
make all proteins, but they only use the sections
of DNA or genes that they need.
• Gene expression is a regulated process.
Cell Differentiation
In a fetus, cells with the
exact same DNA are
directed to differentiate
by chemical signals that
cause certain genes to
be switched on or off in
each one.
Promoter: The Switch
A promoter is a sequence of DNA needed to turn a gene on or off. The process of
transcription is initiated at the promoter. Usually found near the beginning of a
gene, the promoter has a binding site for the enzyme used to make a messenger
RNA (mRNA) molecule.
Repressor
A repressor is a protein that turns off the expression of one or more genes. The
repressor protein works by binding to the gene's promoter region, preventing the
production of messenger RNA (mRNA).
Introns and Exons
• Introns
– Regions of DNA that are not:
• Expressed
• Translated
– Regions that are removed
Introns and Exons
• Exons
– Regions that code for proteins
– Regions that are expressed
– Regions that remain after RNA splicing
Watch for a Demonstration!!!
Epigenome
• The term epigenome is derived from the Greek
word epi, which literally means "above" the
genome.
• The epigenome consists of chemical compounds
that modify, or mark, the genome in a way that
tells it what to do, where to do it, and when to do
it.
• Different cells have different epigenetic marks.
• The environment causes changes in our
epigenetics.
Epigenetics
Use the link below to watch the NOVA video
“Epigenetics”.
http://video.pbs.org/video/1525107473#
DNA Microarrays
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This technology helps scientists understand the differences in
different types of cells, despite the fact that they have the exact
same DNA. DNA microarrays allow scientists to observe which
genes are expressed in different types of cells.