Lecture 32 Flashcards
1
Q
Sterile mutants of yeast)
A
- Lack of cell surface receptors
- Which make up a heterochromatic complex
- They interact with the pheromones, and if there are mutations within this complex, it will not be able to recognise other pheromones, so the phosphorylation cascade will not be activated
2
Q
Ligand binding and GTPases:
A
- Exchange of GDP and GTP is a good way to turn proteins (especially GTP proteins) off and on)
- Intrinsic GTP activity is low without an effector protein, ( they are slow to hydrolyse the GT and add a phosphate)
- GDP is active, GAP activates it, so it increases its GTPase activity, hydrolyses it’s domain and is now inactive.
- Liberate GDP from it’s inactive form using guanine nucleotide dissociation inhibitors (GDI)
- Regulation of gene expression at the protein level by exchanging GTP and GDP
3
Q
Protein processing:
A
- Specifically cleaving proteins to give it different activity
- Specific proteases result in different polypeptide segments which can do different things compared to what it would do if it was cleaved by a different set of proteases
4
Q
Translational control:
A
- Before you make the protein, so controls the timing of protein production
- Can occur at multiple levels
- Destabilising
- Changing when/if translation starts
5
Q
mTor Kinase:
A
- A major regulatory kinase of transitional state
- mTor (mouse Tor kinase) controls when a particular mRNA is translated
- If a particular growth factor is present TorK will phosphorylate 4E-BP
- 4E-BP in the phosphorylated state cannot bind the initiation complex required to recruit other elongation factors and finally the ribosome, translation will occur!
- When 4E-BP is not phosphorylated it can bind, and the elongation factor 4E is kicked out, so it stops the formation of the ribosomal machinery, so no translation occurs
6
Q
Iron regulatory protein:
A
- Iron is required for iron kelators in the body, but too much is toxic, so it must be regulated
- an element can form a secondary structure called the iron regulatory element (a loop in mRNA)
- IRP will bind this secondary structure, preventing the ribosomal machinery assembling, so not translation occurs
- When iron levels increase, it binds to IRP so that it cannot bind the loop so it no longer inhibits the translational machinery, so transcripts are translated
7
Q
Post transcriptional control:
A
- mRNA stability
- mRNA translatability
- This occurs after transcription
8
Q
mRNA stability in RBC:
A
- RBC don’t have nuclei, so the RNA for RBC proteins comes from a progenitor
- RNA encoding hemoglobin must be stable so that they can be translated many times, without needing to replace it
- Stabilisation occurs because of the cell type the mRNA is deposited in
9
Q
mRNA stability in aspergillus nidulans:
A
- Ammonium can be sourced from the environment, but can also be expressed from the genome
- A transcriptional activator encoded by the areA gene is involved in positively acting to transcriptionally regulate genes involve din assimilating nitrogen sources other than ammonium.
- IT binds to the promoters of genes in the absence of ammonium, by creating an mRNA which is translated
- This mRNA has differentially stability based on the presence (10 mins half life) or absence (40 mins) of ammonium
- This difference in timing result due to the binding of de-adenylases on the 5’ polyA tail, which gets shorter and shorter and hence more unstable
10
Q
RNA localisation in saccaromyces cerivisiae:
A
- Mother cells can switch cell type
- If the mother creates two daughter cells, the bigger one is able to switch mating types
- This switching process occurs to HO, homothallic - a cell that can mate with itself, HO is dominant over Ho (must mate with the opposite mating type)
- If Ho gets turned off it can’t switch mating types
- Swi5: found in both mother and daughter cell types
- Ash1: only found the in daughter, not the mother. Ash1 is only translated in the daughter nucleus
11
Q
Post-transcriptional control:
A
- RNA processing including alternate splicing
12
Q
Alternate splicing - negative control:
A
- A primary transcript may splice an intron out in normal conditions
- In a different condition a protein may bind the intron/exon boundary, blocking the machinery from correctly splicing. A protein with a different function may result, or a nonsense protein may occur
13
Q
Alternate splicing - positive control:
A
- The primary transcript will usually leave the intron in and so there is no function or it has a particular action
- An activator protein that binds the RNA helps splicing occur properly, so that a different/functional protein is created by inducing splicing
14
Q
Dosage compensation in sex determination of drosophila:
A
- In mammals, everyone has one lot of X chromosome genes, by inactivating one X chromosome in females
- In flies, the X chromosome in males is upregulated (males are X, females are XX)
- Sex is determined by the ratio of X chromosomes to autosomes.
- Splicing at the sex lethal locus occurs due to having 2 X’s. This leads to female development.
- Only one X chromosome so turns off splicing in sex lethal, turning off the transformer gene. This leads to male development
- This is all post-transcriptional!
15
Q
The ratio of X to autosomes determines what happens at the sex lethal locus (males):
A
- Sxl gene, Tra gene, Dsx gene, male or female.
FOR A MALE: - In a male splicing occurs at the Sex lethal locus, producing a nonfunctional protein product
- The transformer gene produces a non-functional productdue to splicing
- The double sex gene is spliced from the 5’ of intron 1 to the 3’ of intron 2
- This is translated to produce a male-specific amino acid
- This repressed female differentiation genes and male development genes
