gene expression objectives: 1.explain how genes expression is controlled in prokaryotes. 2. explain...
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Gene Expression
Objectives:
1. Explain how genes expression is controlled in prokaryotes.
2. Explain how gene expression is controlled in eukaryotes.
Lac Operon
Promoter
Operator
Repressor
Transcription factors
Gene expression
Cellular differentiation
Stem cell
Pluripotent; Multipotent
Epigenetics
Methylation
Histone Modification
Vocabulary
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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?
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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.
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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.
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Stem cells • Pluripotent (can become any type of cells) or multipotent (many types of cells)
Stem cell researchPotential 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
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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
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Why do people bank cord blood?http://www.thecelebworth.com/top-10-cord-blood-banks/
Sources of Stem Cells1.Embryonic cells (after fertilization to a few weeks)2.Placenta & Umbilical cord blood3.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
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Prokaryotes: Gene ExpressionOperon = Promoter + Operator + GenesPromoter = where RNA polymerase binds.Operator = Where repressor protein binds.
Operon OffRepressor protein binds to operator when lactase is not needed. Stops transcription of
genes.Operon OnLactose 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 systemOperon: 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 whereRepressor protein binds and STOPS TRANSCRIPTION (when proteins are not needed)
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lac operon systemRepressor 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).
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Animation of lac operon systemhttp://www.sumanasinc.com/webcontent/animations/content/lacoperon.htmlMcGraw Hill animation of lac operonhttp://highered.mcgraw-hill.com/sites/dl/free/0072835125/126997/animation27.html
Eukaryotic Gene Expression: Transcription Factors
• More complex than prokaryotes
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More elaborate (than prokaryotes)Genes are not controlled in clusters
Eukaryotes: Gene ExpressionProteins called transcription factors regulate transcription by binding to promoters or RNA polymerase
Turned ON or OFF by chemical signals in the cell
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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/index/238907/epigenetics-how-our-experiences-affect-our-offspring
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The Agouti Micehttp://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. Doctor’sNOVA clip (14min)
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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????
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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
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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
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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 videohttp://www.pbs.org/wgbh/nova/body/epigenetic-mice.html
Gene switches (PBS) slide showhttp://www.pbs.org/wgbh/nova/body/gene-switches.html
Ghost in Your Genes (PBS)https://www.youtube.com/watch?v=8oUJQkUk6P8
Epigenome at a Glancehttp://learn.genetics.utah.edu/content/epigenetics/
Articles for Epigenticshttp://discovermagazine.com/2013/may/13-grandmas-experiences-leave-epigenetic-mark-on-your-genes
http://theweek.com/article/index/238907/epigenetics-how-our-experiences-affect-our-offspring#