‫زیست شناسی مولکولی‬
‫فصل اول‪:‬‬
‫تنظیم بیان ژن در پروکاریوتها‬
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SPECIALIZED GENES
Operator = "on/off" switch for operon
 Regulator = makes repressors to turn off an entire
operon
 Repressor = Binds to operator, turn off gene
expression
 Inducer = Joins with an active repressor,
inactivates it
 Co-repressor = Joins with inactive repressor,
converts it to active

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‫اپرون ها و ریگلون ها‬
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THE OPERON
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OPERON THEORY
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INDUCIBLE OPERONS
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MECHANISMS OF GENE REGULATION
Pathway
Terminology
Ligand
Regulator
Catabolic
Induction
Substrate
Negative (lac operon)
Positive (ara operon)
Anabolic
Repression
Product
Negative (trp operon)
Positive (amino acids in yeast)
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NEGATIVE REGULATORS
[BIND TO
(URS)]
OPERATORS OR UPSTREAM REPRESSION SEQUENCES
Inducer
–
O
Regulator
(Repressor)
Complex
Corepressor
O
–
Regulator
(Aporepressor)
Complex
(Repressor)
Inducible
e.g. lactose operon
Repressible
e.g. trp operon
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POSITIVE REGULATORS
[BIND
TO PROMOTERS, ENHANCERS OR UPSTREAM
ACTIVATION SEQUENCES
(UAS)]
Inducer
+
O
Regulator
+
Complex
"Activator"
Corepressor
Regulator
"Activator"
O
Complex
Inducible
e.g. cAMP
Repressible
e.g. nit-2
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REPRESSIBLE OPERONS
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Lac OPERON THEORY
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Lac OPERON THEORY
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Lac OPERON THEORY
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INACTIVE REPRESSOR-LACTOSE PRESENT
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LAC OPERON
SUMMARY
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Lac OPERON THEORY
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Lac OPERON THEORY
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-HOW THE CAMP-CRP DIMERBINDS TO THE ACTIVATION SITE TO
STIMULATE ATTRACTION FOR THE RNA POLYMERASECRPCRP
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trp OPERON THEORY
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trp OPERON THEORY
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trp OPERON THEORY
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E. COLI TRP OPERON: ATTENUATOR
 UGG
is the codon for tryptophan
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ATTENUATION IN BACTERIA
(COUPLED TRANSCRIPTION AND TRANSLATION)
RNA polymerase
DNA
+H N
3
Protein
Ribosome
mRNA
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‫‪E. COLI TRP OPERON: ATTENUATION‬‬
‫توالي تنظيمي تضعيف كننده در اپرون تريپتوفان‬
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Attenuation model in Trp starved cells.
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Attenuation model in Trp non-starved cells
Animation
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ara OPERON THEORY
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E. COLI ARA OPERON
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E. COLI ARA OPERON: ARABINOSE PRESENT
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E. COLI ARA OPERON: ARABINOSE ABSENT
 Interaction
between dimers bound to I and
O2 sites creates DNA loop and blocks
transcription
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Different from the Lac operon, two
activators AraC and CAP work together to
activate the araBAD operon expression
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