Download Gene Expression

Gene Expression
Objectives:
1. Explain how
genes expression
is controlled in
prokaryotes.
2. Explain how gene
expression is
controlled in
eukaryotes.
Vocabulary
Gene expression
 Lac Operon
 Promoter
Operator
Cellular
differentiation
Stem cell
Repressor
Pluripotent;
Multipotent
Transcription
factors
Epigenetics
Methylation
Histone
Modification
Consider the following…
• Do all of the cells in your
body carry out the same
processes?
• Do all of the cells in your
body make the same
proteins?
• Do all of the cells in your
body contain the same
genes?
• What is the connection
between genes and protein
production?
• How is it possible for
different types of cells to
exist in your body?
Gene Expression


All somatic cells
contain a complete
set of chromosomes
Not all genes get
transcribed and
translated.
Example:
 Skin cells will not
translate genes to
make hemoglobin,
or insulin.
Cell Differentiation
•Differentiation is when cells become specialized in
structure and function
•It results from selective gene expression, the turning
on and off of specific genes.
Stem cells
• Pluripotent (can become
any type of cells) or
multipotent (many types
of cells)
Stem cell research
Potential to help cure/treat
conditions involving damaged
cells (replace cells of damaged
spinal cords, or cardiac
muscles, etc.)
Tutorial on stem cells:
http://www.stemcellresearch.umich.edu/overview/tutorial.html
Stem cells & Therapeutic Cloning

Use embryonic
stem cells to create
specialized human
cells.

Goal: Cure
disease

Embryo does not
develop into a
human.
Allowed in U.S. (state by state) w/ restrictions
Why do people bank
cord blood?
http://www.thecelebwort
h.com/top-10-cordblood-banks/
Sources of Stem Cells
1. Embryonic cells (after fertilization to a
few weeks)
2. Placenta & Umbilical cord blood
3. Bone marrow in adults
What Controls Which Genes Get
Translated (Expressed)?
Prokaryotes (bacteria)
Operon System
Promoter and Operator
sequence before genes
Switch on/off genes
Eukaryotes
Transcription factors
Prokaryotes: Gene Expression
Operon = Promoter + Operator + Genes
Promoter = where RNA polymerase binds.
Operator = Where repressor protein binds.
Operon Off
Repressor protein
binds to operator
when lactase is
not needed.
Stops
transcription of
genes.
Operon On
Lactose present
 binds to
repressor protein.
Repressor
released, genes
transcribed.
Gene Expression in Prokaryotes
& The Lac Operon
Animation
Prokaryotes: lac operon system
Operon: sequence of instructions
for turning on/off transcription.
Located before gene sequences.
Includes “promoter” and “operator”
sequences.
Promoter: RNA polymerase binds
to; “starting line” for transcription.
Operator: site where
Repressor protein binds and STOPS
TRANSCRIPTION (when proteins
are not needed)
lac operon system
Repressor protein: binds to
operator site  prevents
transcription
Repressor proteins alternate shape!
Lactose present: binds to repressor
protein & changes repressor shape;
repressor DOES NOT fit on
operator site; genes transcribed;
proteins for lactose digestion made.
Lactose not present; repressor shape
allows it to bind to operator and
STOP transcription (proteins not
needed).
Animation of lac operon system
http://www.sumanasinc.com/webcontent/animations/content/lacoperon.html
McGraw Hill animation of lac operon
http://highered.mcgraw-hill.com/sites/dl/free/0072835125/126997/animation27.html
Eukaryotic Gene Expression:
Transcription Factors
• More complex
than prokaryotes
Eukaryotes: Gene Expression
Proteins called
transcription
factors
regulate
transcription
by binding to
promoters or
RNA
polymerase
More elaborate (than prokaryotes)
Genes are not controlled in clusters
Turned ON or
OFF by
chemical
signals in the
cell
Eukaryotes: Gene Expression
Epigentics: Gene Expression
Epigenetics
Environmental factors
(chemicals or
temperatures) can activate
or deactivate genes and
influence the expression
of those genes in future
generations.
http://theweek.com/article/index/2
38907/epigenetics-how-ourexperiences-affect-our-offspring
The Agouti Mice
http://www.pbs.org/wgbh/nova/body/epigenetic-mice.html
Epigenetics
• Heritable traits that do not involve changes in
the underlying DNA sequence (“in addition to
changes to the genetic sequence”)
• Used to describe any aspect other than DNA
sequence that influences the development of
an organism.
• Involves chemical modifications that “mark”
certain genes with a distinct signature;
“biological punctuation”
ex) Doctors v. Doctor’s
NOVA clip
(14min)
DNA Packing Helps Regulate
Eukaryotic Gene Expression
•A single chromosome contains app.
4cm of DNA
•Coiling and folding enables all this
DNA to fit in the nucleus
•This packing prevents gene
expression by blocking transcription
(protein contact with DNA)
•Some regions of interphase
chromosomes (chromatin) are highly
packed like mitotic chromosomes
•The genes in these packed regions are
generally not expressed
How are genes
turned on or off?
1. Methylation: Methyl
groups added to DNA turn
off transcription.
2. Histone modification:
Proteins bind to histones
(proteins that DNA is
wrapped around) and causes
histones to tighten DNA
coiling  turn off
transcription
What causes methylation or
histone modification????
Gene Expression: X chromosome
Inactivation
• Female mammals
inherit 2 X
chromosomes, but do
not make twice as
much X-coded proteins
• One X in each somatic
cell condenses into a
compacted, inactive
Barr body.
• The same X is not
turned off in every cell
X Inactivation & Cat Fur - Tortoiseshell
X Inactivation & Cat Fur - Calico
Turning Eukaryotic Genes On & Off
•Eukaryotic RNA
polymerase needs assistant
transcription factor
proteins
•Activator proteins bind to
enhancers (not adjacent to
the gene)
•DNA bends & interacts
with other transcription
factors, facilitating correct
RNA polymerase
Gene Switches
attachment
Alternative RNA Splicing
• More than one type of polypeptide can result from a
single gene
• Different exons are spliced together as a result of
alternative splicing
Homeotic Genes
• Master control genes that
regulate the genes that
actually control the
anatomy of body parts
• Discovered by studying
bizarre fruit fly mutations
• Mutation in a single gene
led to legs growing out of
head in place of antennae
Epigenetics NOVA introduction 13 minutes
http://www.pbs.org/wgbh/nova/body/epigenetics.html
Agouti mice video
http://www.pbs.org/wgbh/nova/body/epigenetic-mice.html
Gene switches (PBS) slide show
http://www.pbs.org/wgbh/nova/body/gene-switches.html
Ghost in Your Genes (PBS)
https://www.youtube.com/watch?v=8oUJQkUk6P8
Epigenome at a Glance
http://learn.genetics.utah.edu/content/epigenetics/
Articles for Epigentics
http://discovermagazine.com/2013/may/13-grandmas-experiences-leave-epigeneticmark-on-your-genes
http://theweek.com/article/index/238907/epigenetics-how-our-experiences-affect-ouroffspring#