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CONTROL OF

GENE

EXPRESSION

EUKARYOTES, PART 2

Chapter 19

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Transcriptional ControlEukaryotic Gene Structure

Eukaryotic Gene  – section of DNA that codes for one or more

related polypeptides or RNA molecules along with the

promoter and regulatory sequences required for expression 

Promoter  – site in DNA where RNA polymerase binds to initiate

transcription; contains conserved sequences including TATA box 

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Transcriptional ControlRegulatory Proteins –  Transcription Factors

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Regulatory Transcription

Factors (TFs)

Different cell types expressdifferent regulatory TFs

TFs are activated in response

to signals received by the cell 

Regulatory Transcription Factors

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Basal transcription

complex:

TFs and RNA pol II

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Regulation of Gene Expression… in Multicellular Eukaryotic Organisms 

Extracellularsignals

Receptor protein in membrane

Intracellularsignals

RegulatoryProteins

(TranscriptionFactors)

1. Signal arrives at cell with message:“Become a muscle cell.” 

Promoter

RNA polymeraseExon Intron Exon Intron Exon

TRANSCRIPTION

Gene for muscle-specific protein

EnhancerEnhancer

Cytoplasm

3. Transcription factors are producedor activated in response to

intracellular signal.

2. Signal transduction results in

production of intracellular signal.

4. Transcription factors bind to regulatorysites in DNA, triggering expression of cell-

specific genes.

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Transcription Initiation

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Transcription Initiation

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RNA Processing

 Alternative Splicing of mRNAs 

Due to alternative splicing,

the number of proteins

that an organism can

produce far exceeds thenumber of genes it has

Introns and exons may be

removed

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RNA Processing

 Alternative Splicing

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mRNA Stability & Interference

Occurs in the cytoplasm

mRNA stability

Presence of 5’ cap and 3’ poly-A tail determine how long mRNA is

active (and therefore how many times it can be translated)

RNA interference (RNAi)/MicroRNAs

Involved in mRNA degradation

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mRNA Stability &

Interference

miRNA – microRNA

RISC - RNA-induced

silencing complex

Could we use these to

treat viral infections?

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Translational Control

Regulatory proteins can add phosphate groups to

proteins in ribosome and slow translation

In response to temperature change

In response to infection

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Post-Translational Control

Post-translational modifications – processing steps that

are required to make a protein functional; such as… 

Protein folding – may require molecular chaperones

Addition of chemical groups (eukaryotes – in ER and Golgi)

Phosphorylation / dephosphorylation

Targeted destruction of proteins –  Proteasome

Proteins tagged with ubiquitin

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Proteasome

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Control of Gene ExpressionProkaryotes vs. Eukaryotes 

Packaging of DNA

Eukaryotes  – tightly packed chromatin; must be

decondensed to begin transcription; default is “off”  Prokaryotes  – less tightly packed; access to promoters;

default is “on” 

Alternative splicing

Eukaryotes  – yes

Prokaryotes  – no

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Control of Gene ExpressionProkaryotes vs. Eukaryotes 

Complexity

Eukaryotes  – more complex; many regulatory proteins

involved Prokaryotes  – less complex

Coordinated Expression (presence of operons)

Eukaryotes  – no

Prokaryotes  – yes