control of transcription dna has “on” and “off” switches activator –protein that binds...
TRANSCRIPT
Control of Transcription
DNA has “on” and “off” switches
Activator –protein that binds near gene’s promoter region
- allows RNA polymerase to transcribe (allows it to fit)
Repressor – protein that binds to DNA and prevents RNA polymerase from binding
-coded for by “regulator” gene
The Operon Model
Operon – region of DNA with group of genes for proteins with related functions
(see diagram)
-All of the genes in the operon are controlled by activity at the promoter & the operator
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Promoterfor I gene
Gene forrepressor protein
Regulatory region Coding region
CAP-bindingsite
Gene forpermease
Operator
Promoter forlac operon
Gene for-galactosidase
Gene fortransacetylase
PI CAP O
ZY A
PlacI
lac control system
The “Lac” Operon-in E. coli bacteria-genes for enzymes to break down lactose sugar
1. Regulator gene codes for Lac repressor protein2. Repressor binds with operator region
If no lactose present:3. RNA polymerase can not bind to promoter, no enzyme made
and operon is “off”If lactose is present:
3. Lactose binds with repressor, repressor no longer binds to operator
4. RNA polymerase transcribes the structural genes• Translation occurs, enzymes are made• Lactose is metabolized
*Conservation of resources – enzymes only made when needed*
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RepressorCAP
CAP
Promoter OperatorcAMP
RNApolymerase
OY
A
IZ
lac operon is "repressed"
Plac
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lac operon is "induced"
CAP
CAP
Promoter Operator
Allolactose(inducer)
cAMP
Plac
RNApolymerase
OY
A
IZ
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mRNA synthesis
CAP-bindingsite
RNA-polymrasebinding site(promoter) Operator
lacZ gene
Operon ? because CAP is not bound
Operon ? both because lac repressor is bound and CAP is not
Operon ? because lac repressor is bound
Operon ? because CAP is bound and lacrepressor is not
RNA polymerase
Repressor
RNA polymerase
CAP
CAP
+
+
+
+G
luco
se
Lac
tose
–
––
–
RNA in Gene regulation“Small RNA’s”
Process of RNA interference (RNAi) or “RNA silencing”-double stranded RNA is cut into small pieces by enzyme called dicer-pieces then unravel into single strands
1. miRNA – micro RNA-binds to a specific RNA thus blocking it from
being translated-reversible2. siRNA – small interfering RNA-binds to specific mRNA, destroys it
Purposes: (evolutionary origins)1. Inactivate viral DNA transcription2. Inactivate transposons – renegade “jumping genes”3. Regulation
Nucleosomes
X- Inactivation