Control of Gene Expression Flashcards
What does beta-galactosidase do?
Hyrolyzes lactose into glucose and galactose
What does galactoside permease do?
Moves lactose into the cell
What food source do bacteria prefer?
Glucose
How does the lac operon behave when glucose is present?
A repressor binds to the operator because the cell is happy with glucose is around and eating lactose is unnecessary.
How does the lac operon behave when lactose is present?
B-gal converts lactose to glu and galac
and also converted into a lactose isomer, allolactose
Allolactose then binds to the operon repressor to allow a teensy bit of gene expression continue
How are cAMP levels affected by glucose levels?
High levels of glucose keep cAMP levels low. When glucose drops, cAMP levels increase
How does cAMP affect lac operon transcription?
cAMP will bind to CRP, binding to the DNA and acting as a lac operon enhancer (high level of transcription)
On a high level, what is the purpose of the lac operon?
To allow the bacteria to mobilize lactose as a food source when glucose availability is low
What motif of CRP interacts with DNA?
Helix-turn-Helix binds to the major groove via H bonds.
Specifically: recognition helix-turn-stabilization helix
How do transcription factors interact with DNA?
Are they specific?
Common motifs that interact with the major groove of DNA. Often are dimers
Very specific!
What are 4 common transcription factor motifs?
- Helix-turn-helix
- Zn finger
- Leucine zipper/bZIP
- Helix-loop-helix
Describe the Zn finger motif
Repetitive motif of 2 cystine and 2 histidine residues
Describe the leucine zipper motif
35 AA stretch with a leucine every 7 + basic alpha helices that interact with the DNA
Describe bZIP
“Leucine” zipper motifs with arginine or histidine in place of leucine
Describe the basic helix-loop-helix motif
Like other motifs, many + charges in the BASIC alpha helix binds DNA
In transcription factor motifs many _____ interactions amount to ____ and _____ binding overall.
Weak, strong, specific
What are the 7 ways in which transcription factors can be regulated?
- Protein synthesis
- Ligand binding
- Protein phosphorylation
- Addition of subunit
- Unmasking
- Stimulation of nuclear entry
- Release from membrane
Generally speaking, will a methylated promoter be active?
No! Methylation will stop transcription
How can cancer co-opt methylation for its own ends?
Methylating tumor suppressor genes turns them off
How does methylation block gene expression?
- Methylated CpG islands inhibit transcription by physically precluding TF recruitment
OR
- Methyl CpG binding protein 2 (MeCP2) binds to methyl groups and recruits chromatin remodeling factors
What causes Rett Syndrome?
Mutations in MeCP2 on the X chromosome
How is Igf2 an example of how methylation can actually lead to activation?
Methylation prevents binding of a repressor
What is ATP-chromatin remodeling?
Chromatin remodeling factors interact with C-terminal of large subunit of RNA Pol II and ATP to “open up” nucleosomes
What ways in which histone tails can be covalently modified?
Methylation (HMT and PRMT)
Phosphorylation (kinase)
Acetylation (HAT)
Which AAs are often modified via methylation to control histones?
Lysine and/or arginine
Which AAs can be modified via acetylation to control histones?
Lysine
Which AAs can be modified via phosphorylation to control histones?
Serine
Histone acetyl transferase (HAT) can acetylate histones…what enzyme removes them?
Histone Deacetylase (HDAC)
Acetylation will _____ chromatin with the exception of _____.
Open
Sometimes methylation of lysine can cause repression.
