Lecture 9 Slides Flashcards
Regulatory genes
Turn genes on and off
What are housekeeping genes
Constitutive genes - expressed all the time
Four levels of regulation of gene expression
- Transcription
- Post transcription
- Translation
- Post translation
Three ways to regulate gene expression post transcription
RNA processing, eg splicing
Rna degradation
Rna transport, eg nuclear export
Half life of prokaryotic rna
Three minutes
Half life of eukaryotic rna
Minutes to hours
What does regulation depend on during translation
Whether or not ribosome can translate mRNA
Three ways to regulate gene expression post translation
Affect protein stability - some proteins denature easily
Some proteins are targeted for degradation
Modifications eg phosphorylation
Example of negative control in transcription
Repressing splicing so intron is not removed
Positive control example during transcription
Using an activator to make splicing happen
At what point in ponytail does mRNA start to degrade
When there are 25 or fewer adenines
Is mRNA decamped before degradation
Yes
In what direction does degradation happen
5’ to 3’
What initiation factors initiate translation
EIF4G and eIF4E
What enzyme degrades poly A tail
Deadenylase
What is a translation repressor protein
A protein that blocks the start codon AUG
How can a newly synthesized protein fold?
- Correctly folded without help
- Correctly folded with help of a molecular chaperone
- Incompletely folded and digested by the proteasome
What digests a protein that is incompletely folded
A proteosome
What kind of cells have proteosomes in the cytosol
Eukaryotes, archea, and some bacteria
What is Ubiquitin ligase
An enzyme that binds Ubiquitin
Where is Ubiquitin added to unwanted protein
To side chain, ends with N terminal. Add c terminal end of Ubiquitin.
Polyubiquitin
More than one Ubiquitin has been added to unwanted protein
What happens to unwanted protein once Ubiquitin has bound to it
It goes to a proteosome, where it is unfolded. Ubiquitin doesn’t go in. Amino acids are recycled.
How many amino acids in Ubiquitin
72
How many lysine residues in Ubiquitin
Seven
What are the two subunits of Ubiquitin ligase? What is their function.
E2- Ubiquitin transferase
e3- recognizes target protein
What is E1 unit
It is the carrier of Ubiquitin
What does E1 do with the Ubiquitin it carries
It charges E2
What do proteosome target proteins have
PEST motif, which is phosphorylated
Destruction box
Amino acid sequence required for degradation
n-end rule
N-terminal amino acid of a protein determines its half life (likelihood of being degraded)
How is Ubiquitin ligase activated
Phosphorylation by protein kinase
Allosteric transition by ligand binding or protein subunit addition
How is a degradation signal activated
Phosphorylation by protein kinase
Unmasking by protein dissociation
Creation of destabilizing N-terminus
Density and molecular weight of proteosome
26s
2.5 MDa
Proteosome subunits
19s cap 20s cylinder (active site)
What is active site of proteosome
20s cylinder
What does unfolding and pulling of protein throufh cylinder require
ATP
How does target protein attach to proteosome
At unfoldase ring
Contents of cap of proteosome
Ubiquitin receptor
Unfoldase ring
Ubiquitin hydrolase (to release Ubiquitin)
Shape of unfoldase ring
Hexameric
Is inactivation by polyubiquination reversible
No
Cell life cycle phasesq
Interphase - G1, S phase, G2
M phase- mitosis and cytokinesis
What is cyclin
An enzyme whose concentration varies with stages of cell life cycle
When is cyclin concentration high? Low?
High in mitosis
Low during interphase
