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REGULATION OF GENE REGULATION OF GENE EXPRESSIONEXPRESSION
WHY REGULATE GENE EXPRESSION??
Adaptation
(Energy Conservation) Development and differentiation
GENE EXPRESSION IN DIFFERENT CELLS
Muscle cell Pancreatic cells alpha cells beta cells
Blood cellsWBCs RBCsGenes for
Glycolysis ON ON ON ON ON
Insulin OFF OFF ON OFF OFF
Glucagon OFF ON OFF OFF OFF
Hemoglobin OFF OFF OFF OFF ON
A PROKARYOTIC AND A PROKARYOTIC AND EUKARYOTIC CELLEUKARYOTIC CELL
REGULATION OF GENE REGULATION OF GENE EXPRESSION - EXPRESSION - PROKARYOTESPROKARYOTES
THE OPERONTHE OPERON
DNA
Promoter Gene 1 Gene 2 Gene 3
Structural Genes
5’ 3’
AUG AUG AUGUAA UGA UAGPolycistronic mRNA
Protein 1 Protein 2 Protein 3
Operon
REPRESSORSREPRESSORS
3’
mRNA
Promoter Gene 1 Gene 2 Gene 35’
Operator
No transcription
No protein products
Regulatory gene
RepressorRNA polymerase
REGULATORY MECHANISMSREGULATORY MECHANISMS
INDUCTIONRepressor is INACTIVATED through inducers to INITIATE / INDUCE transcription REPRESSION
Repressor is ACTIVATED through corepressors to PREVENT / REPRESS transcription
INDUCTIONINDUCTION
Inducer
Inactive repressor
Active repressor
No transcription, translation
Transcription
Translation
REPRESSIONREPRESSIONInactive repressor
Corepressors
Transcription
Translation
No transcription, translation
Active repressor
GENE REGULATION IN EUKARYOTES
Gene Regulation Can Take Place at Many Levels
Chromosome
Transcription
Processing of transcripts
Translation
GENE REGULATION AT THE CHROMOSOMAL LEVEL
Two Types of Chromatin Two Types of Chromatin
• HETEROCHROMATIN Trancriptionally inactive
tightly condensed
• EUCHROMATIN
Transcriptionally active
Relatively relaxed
CHROMATIN CHROMATIN STRUCTURESTRUCTURE
EFFECT OF CHROMATIN STRUCTURE ON TRANSCRIPTION
Control region outside nucleosome
GENE IS ACTIVE
Control region within nucleosome
GENE IS INACTIVE
Histone AcetylationHistone Acetylation
HAT
Histone AcetylationHistone Acetylation
DNA MethylationDNA Methylation
X-InactivationX-Inactivation
• Inactive X-Chromosome (Barr body)– Underacetylated at H4– Hypermethylated
X-inactivation in humansX-inactivation in humans
• Red-green color blindness– Males = fully color blind– Females = mosaic retinas
• Anhidrotic ectodermal dysplasia– Males = absence of teeth, lack of sweat
glands– Females = random patterns of tissue with or
without sweat glands
Arrangement of DNA
Antibody Diversity• Light chains:
– Up to 300 Variable, 4 Joining and 1 Constant region• 300 x 4 = 1, 200 light chains
• Heavy chains: – Up to 500 Variable, 4 Joining and 12 Diversity
regions and 12 constant regions• 500 x 4 x 12 = 24, 000 light chains
1200 x 24,000 = 28,800,000 antibody molecules
REGULATION AT THE LEVEL OF TRANSCRIPTION
• GTFs only produce a basal level of transcription i.e. very low
• Gene-specific factors (activators) are further required to regulate the activity of gene expression
Enhancers/Silencers
• Upstream or downstream• Close to the promoter or thousands of base
pairs away• On either of the two strands of DNA• Act through intermediary or gene specific
transcription factors proteins• Enhancers activate transcription • Silencers deactivate transcription
Enhancers/Silencers
Response Elements•Enhancers contain response elements that
are responsive to certain metabolic factors
–Cyclic AMP response element (CRE)–Glucocorticoid response element (GRE)–Heat shock element (HSE)
•REs bind transcription factors produced under certain cell conditions to activate several related genes
cAMP Response Element (CRE)cAMP Response Element (CRE)
5’- TGACGTCA -3’
3’- ACTGCAGT -5’
CREB – the most important protein CREB – the most important protein that you have never heard ofthat you have never heard of
• Implicated in – Cell proliferation– Cell differentiation– Spermatogenesis– Release of somatostatin (inhibitor growth hormone)– Development of T lymphocytes– Metabolism of the pineal gland– Adaptation to physical stress– Transcription of metabolic enzymes– Critical in learning and long term memory
Activation of CREB
Glucocorticoid Response Element Glucocorticoid Response Element
GENE REGULATION BY PROCESSING OF TRANSCRIPTS
Alternative Splicing
RNA EDITING
Regulation of Translation byRegulation of Translation byPhosphorylationPhosphorylation
mRNA mRNA StabilityStability
Regulation of Transferrin Regulation of Transferrin ExpressionExpression
Regulation of ferritin Regulation of ferritin expressionexpression
RNA Interference
…will be done with therapeutics
The End!