Gene Expression

1
Gene Expression
Vocabulary

• Objectives
• Explain how genes expression is controlled in
  prokaryotes.
• 2. Explain how gene expression is controlled in
  eukaryotes.

• Gene expression
• Cellular differentiation
• Stem cell
• Pluripotent Multipotent
• Epigenetics
• Methylation
• Histone Modification

• Lac Operon
• Promoter
• Operator
• Repressor
• Transcription factors

2
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?

3
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.

4
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.

5
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.stemcellresea
rch.umich.edu/overview/tutorial.html
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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
7
Why do people bank cord blood? http//www.theceleb
worth.com/top-10-cord-blood-banks/

• Sources of Stem Cells
• Embryonic cells (after fertilization to a few
  weeks)
• Placenta Umbilical cord blood
• Bone marrow in adults

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What Controls Which Genes Get Translated
(Expressed)?

• Prokaryotes (bacteria)

Eukaryotes

• Operon System
• Promoter and Operator sequence before genes
• Switch on/off genes

Transcription factors
9
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.
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Gene Expression in Prokaryotes The Lac Operon
Animation
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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)
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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).
13
Animation of lac operon system http//www.sumanasi
nc.com/webcontent/animations/content/lacoperon.htm
l McGraw Hill animation of lac operon http//highe
red.mcgraw-hill.com/sites/dl/free/0072835125/12699
7/animation27.html
Eukaryotic Gene Expression Transcription Factors

• More complex than prokaryotes

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Eukaryotes Gene Expression

• Proteins called transcription factors regulate
  transcription by binding to promoters or RNA
  polymerase
• Turned ON or OFF by chemical signals in the cell

• More elaborate (than prokaryotes)
• Genes are not controlled in clusters

15
Eukaryotes Gene Expression
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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/ind
ex/238907/epigenetics-how-our-experiences-affect-o
ur-offspring
17
The Agouti Mice
http//www.pbs.org/wgbh/nova/body/epigenetic-mice.
html
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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. Doctors

NOVA clip (14min)
19
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

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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????
21
(No Transcript)
22
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

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X Inactivation Cat Fur - Tortoiseshell
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X Inactivation Cat Fur - Calico
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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
  attachment

Gene Switches
26
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

27
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

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Epigenetics NOVA introduction 13 minutes
http//www.pbs.org/wgbh/nova/body/epigenetics.html
Agouti mice video http//www.pbs.org/wgbh/nova/b
ody/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?v8oUJQkUk6P8
Epigenome at a Glance http//learn.genetics.utah.
edu/content/epigenetics/ Articles for
Epigentics http//discovermagazine.com/2013/may/13
-grandmas-experiences-leave-epigenetic-mark-on-you
r-genes http//theweek.com/article/index/238907/e
pigenetics-how-our-experiences-affect-our-offsprin
g