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REGULATION OF GENE EXPRESSION (:check: Arabinose Operon (Positive…
REGULATION OF GENE EXPRESSION
Transcription Control
Promotors
Key of controlling transcription
:arrow_right: bc it determines where transcription begins
consists of
consensus sequence
the most commonly encountered nucleotides found at a specific location of DNA or RNA
made by comparing nucleic acid sequences among species
:pen:
different between weak and strong(TATA box) promotors
classified as
strong or weak
according to
its affinity for RNA polymerase
Aid the recognition of RNA polymerase and other transcription factors to initiate transcription :red_flag: they require specific distance between promoter parts
-35 and -10
:pencil2:
upstream
at the
5' end
of the transcription initiation site
Activator binding site
binding site for
activator
proteins :warning: promotes the transcription
behind
promotor
Operator
binding sites for
repressor
protein :warning: inhibits the transcription
after
promotor
:star: recognizes and acts on
environment cues
Regulatory protein
interaction btwn 2 sites of protein (:one:DNA binding site :two:Allosteric site) :arrow_right: determine the function
Genetic Evidence
:check: using
lac
operon
Oc mutation
:arrow_right: non-functional Operator :arrow_right: makes
repressor
cannot bind to Operator :arrow_right:
Operon is always ON
:warning:
cis-acting
elements regulate the transcription of
adjacent genes
:arrow_right: restricts the effect of mutation :arrow_right: only one
lac
operon is inhibited
I mutation
:arrow_right: non-functional Repressor :arrow_right:
Operon is always ON
:warning:
trans-acting
elements regulate distant genes from its origin gene
General Knowledge
Regulation of gene is essential
Multicellular organism :arrow_right: allows cells to behave appropriately (
specific cells do specific jobs
)
Single cellular organism :arrow_right: to sense and respond to the environment
:fire: Mechanism
Transcription (
DNA :arrow_right: RNA
)
Gene copy number :arrow_forward:
more genes :point_right: more product
Transcription efficiency :arrow_forward:
RNA polymerase activity
Translation (
RNA :arrow_right: Protein
)
mRNA stability :arrow_forward:
control the half life time of mRNA
:!: whether or not it is translated
mRNA translation
:arrow_forward: Efficiency of translation :point_right: ribosome binding
:arrow_forward: Rate of translation :point_right: codon usage
Folding (
Protein :arrow_right: Enzyme activity
)
Protein stability :arrow_forward:
control the half life of protein
Post-translation effects :arrow_forward:
protein structure and modification
:check: eg kinase adds phosphate group to protein :arrow_right: alters protein behaviour
:check:
Lac Operon
eg of
transcription control
of B-Galactosidase, Permease, Transacetylase
for uptaking lactose
(in the form of glucose and galactose)
In response to environment cues
Glucose present :arrow_forward: best Energy :arrow_right: no need to breaking down
Lactose
presence of
Lactose
is responded by
lac repressor
at
operator
presence of
Glucose
is responded by
cAMP :arrow_right: CAP:cAMP complex
at
promotor
:warning: Lactose :check: Glucose :green_cross: :arrow_right:
highest
efficiency of transcription
:warning: Lactose :green_cross: Glucose :check: :arrow_right: OFF
:warning: Lactose :check: Glucose :check: :arrow_right:
lowest
efficiency of transcription
Negative regulation system
:no_entry:
:cry:
No lactose present
:arrow_right: Repressor protein (
lac repressor
) binds to
Operator
:arrow_right: interrupt RNA polymerase's way
:laughing:
Lactose present
:arrow_right: lactose binds
allosterically
to
lac repressor
:arrow_right: inhibit it binds to
Operator
Positive regulation system
:smiley:
cAMP forms a complex with CAP (catabolite activator protein)
:arrow_right: CAP:cAMP binds to
Promoters
:arrow_right: causes
bending of DNA sequence
:arrow_right: improve the binding site of RNA polymerase :arrow_right:
promote the transcription
Glucose levels regulate cAMP levels
:arrow_right:
High
glucose :arrow_forward: No cAMP
:arrow_right:
Low
Glucose :arrow_forward: cAMP production (from ATP)
:check:
Arabinose Operon
Positive regulation
:smiley: :arrow_right: in the
presence
of arabinose
AraC+
arabinose allosterically
protein binds to
AraI
:arrow_right: initiate transcription
CAP:cAMP binds to
AraO
control sites
:arrow_right: AraO and AraI
Negative regulation
:no_entry: :arrow_right: in the
absence
of arabinose
AraC binds to
AraI
and
AraO
:arrow_right:
DNA loop formation
:arrow_right: :no_entry: the transcription
ArC can be activator or repressor
eg of
transcription control
Translational Control
:check:
Tryptophan operon
:warning: can also be
transcription control
by
repressor protein
:right same as
negative regulation
of lac operon
Leader sequence
160bp in
btwn Operator and trpE
in
DNA sequence
:open_mouth:
mRNA sequence
part of it act as
Attenuator
in
mRNA sequence
incl
2 tryptophan codons
in
mRNA sequence
can
base pair
to form
three stem lopp structure
(Attenuation)
High
tryptophan level
segment :one: :arrow_right: translated
segment :two: :arrow_right: enters ribosome :arrow_right:
prevent the hybridization of :two: & :three:
:three: & :four: :arrow_right:
hybridized
:arrow_right:
terminate the transcription
:arrow_right: no tryp is made
Low
tryptophan level
Translation stalled at segment :one:
:two: & :three: :arrow_right:
hybridization
:three: & :four: :arrow_right:
can't paired
:arrow_right:
no terminate transcription
:arrow_right: tryptophan is made
Attenuation
is possible in
prokaryote
be translation and transcription occur
simultaneaously
Regulation in
Eukaryote
similarities
:two_women_holding_hands:
Promoter is
variable
to specify transcription initiation
Use
activator
and
repressor
protein
differences
:fist-2:
Chromatin regulation
in Normal state
prokaryote
DNA is ON :arrow_right: RNA polymerase binds and initiates trancription
eukaryote
DNA is OFF :arrow_right:
nucleosome
structure (tensed) blocks RNA polymerase binding
Required to remove
introns
of mRNA before
translation
Transcription and Translation occur at
different places at different times
(transcription :arrow_forward: translation)
Transcription
controlled by
:arrow_right:
promotor
(upstream to the gene) and
enhancer
(distant to the gene)
:one: Activator stimulate
Initiation
at
distant
sites
:two: Transcription factors bind to
promotor
:arrow_right: promotes
RNA polymerase
binding :smiley:
:three:
Mediator protein complex
interacts with
activator
,
TFs
&
RNA polymerase
(
:warning: loop formation
) :arrow_right: promote transcription :laughing:
:check:
GAL system
Multiple genes involved (GAL :one:, :two:, :seven:, :one::zero:) :warning: BUT not in
OPERON
GAL :four: (unlinked regulatory gene) expressed in
ABSENCE
of glucose
:arrow_right: activator binding sites are upstream of those GAL :point_right:
Upstream activator sequences
Galactose :green_cross::
:arrow_right: Repressor Gal80p binds to Gal4p :arrow_right:
prevents Gal4p activate transcrption
Galactose :check: Glucose :green_cross:
:arrow_right: Gal3p converts galactose :arrow_forward:
inducer
:arrow_right:
prevents Gal80p binding Gal4p
:arrow_right: Gal4p recruits RNA polymerase for transcription ( :point_down:following steps below)