unit 4 proteins transcription (dna to mrna) translation (mrna to trna to proteins) gene...
TRANSCRIPT
Unit 4• Proteins• Transcription (DNA to mRNA)• Translation (mRNA to tRNA to proteins)• Gene expression/regulation (turning genes on and off)• Viruses
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Yesterday’s Exit Ticket
Template DNA 3’ T A C A A T G C A T T G __’
Non-Template 5’ A T G T T A C G T A A C __’
mRNA 5’ A U G U U A C G U A A C 3’
1) Fill in the blanks.2) What is the amino
acid sequence corresponding to the DNA and RNA sequences below?
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Met-Leu-Arg-Asn
Today’s Plan
• What is gene regulation? Why do cells do it?• How genes are regulated
– Bacteria– Eukaryotes
• Mechanisms of Development
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GENE REGULATIONGENE REGULATIONWhat is gene regulation?
• Turning genes on and off in the right time and place• Controlling the quantity of proteins produced
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GENE REGULATIONGENE REGULATIONWhy do genes need to be regulated?
• Every cell in our body has the same set of genes
• Our body consists of trillions of cells and millions of distinct cell types.
What makes a skin cell different from a liver cell?
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Why do genes need to be regulated?
1. Differentiated structures/organs2. Not all of a single cell’s functions are needed all the
time (e.g. we shouldn’t make insulin constantly)
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Why do genes need to be regulated?
1. Differentiated structures/organs
2. Not all of a single cell’s functions are needed all the time (e.g. we shouldn’t make insulin constantly)
3. Waste of energy/molecules to express genes whose products are not needed
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Why do genes need to be regulated?
1. Differentiated structures/organs
2. Not all of a single cell’s functions are needed all the time (e.g. we shouldn’t make insulin constantly)
3. Waste of energy/molecules to express genes whose products are not needed
4. Some functions are mutually exclusive; two enzymes may have opposite functions
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Examples: different cell types within a human• Muscle cells express muscle actin and myosin• Hair and nail cells express keratin• Blood cells express hemoglobin
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Today’s Plan
• What is gene regulation? Why do cells do it?• How genes are regulated
– Bacteria– Eukaryotes
• Mechanisms of Development
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“…Consider, for instance, an individual E. coli cell living in the...human colon, dependent for its nutrients on the whimsical eating habits of its host” textbook, p. 352
tryptophan present?
tryptophan present?
YES
no need to synthesize tryptophan
no need to synthesize tryptophan
NO
need to synthesize tryptophan
need to synthesize tryptophan
express genes for tryptophan synthesis
express genes for tryptophan synthesis
HOW?HOW?
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How can a cell do this, with no “brain” or “intelligence” directing it?
Molecules can act as signals by directly influencing
transcription
Molecules can act as signals by directly influencing
transcription13
How does this really work?
Example: E. coli regulation of tryptophan
(1) turning multiple genes “on” and “off”(2) doing so at the appropriate times
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Sweatblock.com; netropolus.com
Negative Feedback
If something is present, don’t make more of it!
-
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Gene regulation in bacteriaGene regulation in bacteria
Operator: the “on-off switch” that controls the access of RNA polymerase to the genes
Operon: promoter, operator, and genes
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(2) expressing the genes of the operon at the right time
For the trp operon, RNA polymerase can bind when nothing is bound to the operator
For the trp operon, RNA polymerase can bind when nothing is bound to the operator
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(2) expressing the genes of the operon at the right time
How do we stop repression?How do we stop repression?
• Binding of tryptophan to repressor is reversible
• Repressor activation/deactivation depends upon relative concentrations of tryptophan and repressor protein
• Binding of tryptophan to repressor is reversible
• Repressor activation/deactivation depends upon relative concentrations of tryptophan and repressor protein
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Today’s Plan
• What is gene regulation? Why do cells do it?• How genes are regulated
– Bacteria– Eukaryotes
• Mechanisms of Development
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Eukaryotes:Differential Gene Expression
• Differences between cell types result from differential gene expression
(a) Fertilized eggs of a frog (b) Newly hatched tadpole22
Fig. 18-6
DNA
Signal
Gene
NUCLEUS
Chromatin modification
Chromatin
Gene availablefor transcription
Exon
Intron
Tail
RNA
Cap
RNA processing
Primary transcript
mRNA in nucleus
Transport to cytoplasm
mRNA in cytoplasm
Translation
CYTOPLASM
Degradationof mRNA
Protein processing
Polypeptide
Active protein
Cellular function
Transport to cellulardestination
Degradationof protein
Transcription
In eukaryotes, gene expression can be regulated at many different stages.
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Fig. 18-6a
DNA
Signal
Gene
NUCLEUS
Chromatin modification
Chromatin
Gene availablefor transcription
Exon
Intron
Tail
RNA
Cap
RNA processing
Primary transcript
mRNA in nucleus
Transport to cytoplasm
CYTOPLASM
Transcription
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Fig. 18-6b
mRNA in cytoplasm
Translation
CYTOPLASM
Degradationof mRNA
Protein processing
Polypeptide
Active protein
Cellular function
Transport to cellulardestination
Degradationof protein
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How is transcription regulated in eukaryotes?
Promoters and introns aren’t the only non-coding regions of DNA!
Meet the Enhancers:
http://bja.oxfordjournals.org
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How is transcription regulated in eukaryotes?
Liver enhancer Liver gene (enzyme)
Lens gene (crystallin)Lens enhancer
Promoter
Meet the Enhancers: • DNA control regions corresponding to a specific gene• Can be upstream, downstream, or in an intron• Comprised of control elements
Control Elements
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How is transcription regulated in eukaryotes?
Liver enhancer Liver gene (enzyme)
Lens gene (crystallin)Lens enhancer
Promoter
How does a DNA region control a gene? • Through activators specific to each control element• Activators are specialized transcription factors (proteins)
Control Elements
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Liver enhancer Liver gene (enzyme)
Lens gene (crystallin)Lens enhancer
Liver cell Lens cell
Lens activatorsLiver activators
Pro.
Pro.
Lens gene ON
Liver gene ON
Lens gene OFF
Liver gene OFF
Animation
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Today’s Plan
• What is gene regulation? Why do cells do it?• How genes are regulated
– Bacteria– Eukaryotes
• Mechanisms of Development – Example of malformed frogs
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Development
1. Determination and Differentiation2. Getting the right parts in the right places:
Pattern formation
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(a) Fertilized eggs of a frog (b) Newly hatched tadpole
one zygote many cell types, tissues, organs
cell division (mitosis), differentiation, morphogenesis
The key is differential gene regulation
1. Differentiation and determination1. Differentiation and determination
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The process of development: some useful terms
1. Differentiation and determination1. Differentiation and determination
When I grow up I will be a heart cell!
Better start making actin and myosin!
Hello, my name is
Celly
Hello, my name is
Celly
You’re a heart cell too! Yay!
Hello, my name is
Celly
Hello, my name is
Cella36
TWO COMPLEMENTARY MECHANISMS of DIFFERENTIATION
• Cytoplasmic Determinants before fertilization, when eggs are made maternally derived
• Inductive Signals once there are multiple cells substance from outside a cell (e.g., signal from nearby cell) influences cell’s gene expression
1. Differentiation and determination1. Differentiation and determination
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(a) Cytoplasmic determinants
Two differentcytoplasmicdeterminants
Unfertilized egg
Sperm
Fertilization
Zygote
Mitoticcell division
Two-celledembryo
Nucleus
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(b) Induction by nearby cells
Signalmolecule(inducer)
Chain reaction
Early embryo NUCLEUS
Signalreceptor
1. Differentiation and determination1. Differentiation and determination
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Embryonicprecursor cell
Nucleus
OFF
DNA
masterregulatory gene myoD Other muscle-specific genes
OFF
has potential to develop into a variety of different cell types
has potential to develop into a variety of different cell types
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OFFmRNA
MyoD protein(transcription factor)
Muscle cell precursor(determined)
Embryonicprecursor
cell
Nucleus
OFF
DNA
Other muscle-specific genes
OFF
masterregulatory gene myoD
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mRNA mRNA mRNA mRNA
muscle proteins
Part of a muscle fiber(fully differentiated cell)
MyoD Anothertranscriptionfactor
OFFmRNA
MyoD protein(transcription factor)
Embryonicprecursor cell
Nucleus
OFF
DNA
Other muscle-specific genes
OFF
Muscle cell precursor(determined)
masterregulatory gene myoD
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Outline
1. Determination and Differentiation2. Getting the right parts in the right places:
Pattern formation
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Pattern Formation: Setting Up the Body Plan
• Pattern formation = development of spatial organization of tissues and organs establishment of major body axes
• Positional information = molecular cues that tell a cell its location
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Cytoplasmic determinants in eggs are products of maternal effect genes (a.k.a. egg polarity genes)
Unfertilized egg
unevenly distributed RNA,proteins (from
mother)
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A closer look at the formation of the anterior-posterior (head-tail) axis:
the bicoid gene
Presence of bicoid protein = “put head here”OR
Lack of bicoid protein = “head does not go here” 48
Cytoplasmic determinants in eggs are products of maternal effect genes (a.k.a. egg polarity genes)
Unfertilized egg
unevenly distributed RNA,proteins (from
mother)
mutation in maternal effect gene
mutation in maternal effect gene
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Today’s Take-Homes:
• Gene expression can be regulated at many stages
• Transcription regulation is a common mechanism
• Eukaryotes use enhancers and activators for differential gene expression
• Protein concentrations from mom’s egg play a key role in development
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