Symes Control of Gene Expression Flashcards
When is the Lac operon switched on?
If no Glucose is present
Z gene lac operon
ß-galactosidase
- converts lactose into glucose and galactose
Y gene lac operon
Galactoside permease
- brings lactose into cell
a gene lac operon
Thiogalactoside transacetylase, don’t need to know what it does
I gene lac operon
Encodes repressor
o gene lac operon
RNA Polymerase binding site
CRP gene lac operon
cAMP receptor protein binding site
How does glucose affect the presence of cAMP in the cell and if it will bind CRP
High glucose = low cAMP, low CRP
Low glucose = high cAMP, high CRP
Ratio of proteins generated from genes Z, Y and A in the lac operon
10:5:2
If there is only Glucose present, what is occurring with the lac operon?
The I gene produces the repressor protein which binds to O to prevent RNA Pol from binding
Go through what happens in the cell if Lactose is present
1) Permease brings lactose into the cell
2) ß-galactosidase breaks down lactose and convert some into allolactose
3) Allolactose binds the repressor allowing transcription to occur
4) cAMP binds CRP, causing it to bind the CRP region
5) CRP binding stimulates RNA Pol to bind promoter, high levels of transcription
What is CRP
Protein which stimulates RNA Pol to bind the promoter to increase transcription to a high level
Helix-turn-helix motif
Present in almost all prokaryotic and in some eukaryotic TFs
- recognition helix, turn, stabilization helix
- stab helix binds major groove
- dimer
What do we need to know about the ß-pleated sheet motif?
it exists
How is the Zinc finger formed?
The presence of Zinc causes interactions which forms the finger (which is an alpha helix)
What is the structure of the Leucine Zipper motif?
A dimer of basic regions binds the DNA, while two alpha helices create the zipper portion
- Leucines sticking out of the alpha helices interact with each other to form the zipper
What is the bZIP motif?
Same as Leucine zipper, but Leucine is replaced with a different hydrophobic amino acid
What is the basic helix-loop-helix motif?
A dimer which binds the alpha helix major groove. Its structure contains a basic alpha helix DNA binding region. It has a zipper, but it includes a non-helical loop in each monomer.
What is the importance of heterodimers in TF motifs?
They allow for interactions with regulatory proteins
How do CpG islands inhibit transcription?
Their methylation recruits CpG Island Binding Proteins such as histone deacetylases
What is the Imprinting concept?
Once copy of the gene received from the sperm or egg is methylated. If the methylation flips to the other copy, that can lead to disease
Prader-Willi
obesity, short stature, hypogonadism
- 75% due to loss of non-methylated gene
- 25% due to trisomy
trisomy is extra imprinted gene, loss of non-imprinted gene
Angelmann’s syndrome
Epilepsy, tremors, perpetually smiling
- 75% loss of imprinted
- 25% trisomy
trisomy is extra imprinted gene, loss of non-imprinted gene
Effect of absent T3 on Thyroid receptor
The lack of T3 causes TR and RXR to bind the corepressor complex, activating its HDAC domain. This then prevents transcription
RXR: Retinoid X Receptor
Effect of present T3 on thyroid receptor
The T3 binds TR, the corepressor complex leaves and the coactivator which has an HAT domain binds, activating transcription
HAT: Histone Acetyltransferase
Which histone modification causes transcriptional repression?
Methylation of Lysine depending on location
histone tail modifications usually support transcription
What is the structure of CRP?
- helix-turn-helix motif
- dimer
Where does the Zinc finger sit?
DNA major groove
Why does the Zinc finger not need to dimerize?
The presence of multiple motifs causes multiple interactions (ie. fingers) which negates the need for dimerization
Prader-Willi and Angelmann’s syndrome are a result of a malfunction in which methylation process?
Imprinting
What is Igf-2 methylation an example of?
Imprinting of a gene can actually activate transcription, instead of inhibiting it. The methylation prevents binding of a repressor to allow transcription
