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MOLECULAR BIOLOGY AND GENETICS
Regulation of gene expression in bacteria
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Martha Ayikoru
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Transcription
RNA
synthesis from
DNA
template
Translation
Protein synthesis from
RNA
template
Gene expression
information in
genes
is converted into
functional
products/proteins
gene expression starts with
Transcription
promoters
binding of
RNA polymerase
at specific
regulatory
sites
Regulatory
elements
Cis-acting
regulatory
elements
upstream in
bacteria
/
prokaryotes
regulatory
elements
present in
mRNA
and are essential for the process of
translation
Translation
ribosomal
binding at 5’ untranslated regions and terminates the
3’
UTR
Bacteria
Lacks spatial separation in
transcription
and
translation
Eukaryotes
have
spatial separation
both in
transcription
and translation
Levels of regulation in bacteria
Transcriptional
regulation
Post-transcriptional
regulation
Translational
regulation
Post-translational
regulation
Regulation in transcription
Base pairs in
-35
and
-10
boxes that allow gene expression at different levels
gene expression is regulated in response to
cell metabolic
need
various
cellular
process
environmental
conditions
Inducible control system
bacterial
cell
induce the
synthesis
of
enzymes
Lac operon
Three
enzymes
;
lac
z
,
y
and
a
b-galactosidase
converts disaccharide lactose
into
monosaccharide glucose
and
galactose
lac y
encodes
permease
Permease
facilitates entry
of
lactose
into the
cell
Lac A
encodes
transacetylase
Transacetylase
removes toxic by-products
of
lactose
from the
bacterial cell
How does lactose induce the expression of the lac operon?
Gratituous
inducer
constitutive
mutations
Gratitous inducer
chemical molecule
that doesn’t get
metabolized
by the
products
of the
lac operon
Constitutive mutations
mutations
that allow
continuous transcription
of
structural genes
in
bacterial operon
regulation of lac
operon
inducible
because
genes
are only
turned
on when
induced
in the
presence
of
lactose
If lactose is absent
enzymes are not produced
Lac operon
subject to
negative control
Negative control
transcription
only occurs when
repressor
fails to bind to the
operator region
Lac repressor
Regulated
by
lac L gene
Lac L gene
Constitutive gene
(
360 aas
)
Lac l
Produces
an
allosteric repressor
Allosteric repressor
Reversible interaction
that causes a
change
in the
chemical activity
and also a
conformational change
Allosteric repressor
has
two active sites
site that binds
repressor
to the
DNA
site that binds
lactose
to the
repressor
and induce and
allosteric change
Lac Z
Encodes
B-galactosidase
Effects of Lac L gene mutations
Affect either/
both
sites of the
lac L
gene
Alter the
operator
binding site of the
repressor
to prevent the
binding
of the
repressor
to the
operator
Eliminate
the
inducer
binding sites have the
opposite
effect.
Lack of the Lac L gene can also significantly promote
lactose metabolism.
Merozygote
generating
a
partially diploid organism
The Lac O gene and effects of its mutations
Constitutive activation
of the
lac operon
but not
through
the
production
of
A.
Altered operator sequence
that can no longer
interact
with the
repressor.
Cis-acting
Operator
Transacting
repressor
Cis-acting
Affect activity
of
genes
on which it is
joined
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