protein sorting and intracellular traffic Flashcards
Is the nuclear envelope continuous with the ER?
yes
What is the main difference of function of the SER and RER
RER: Protein synthesis
SER: Lipid synthesis
What does the SER do?
1) synthesis of lipids
2) Synthesis of steroid hormones
3) Storage and release of Ca2+
4) Detox
Give examples of where in the body has a dense volume of SER
Liver and adrenal cortex
Give an example of a protein made in the cytosol
AKT, synthesised by free ribosomes
What is the process of proteins being transported in the ER during protein synthesis called?
Co-translational translocation
How does a ribosome bind to the RER?
A signal sequence is synthesised in the ribosome through the mRNA, which allows it to attach to an SRP. The SRP then attaches to an SRP receptor in the rough ER membrane
What happens to the SRP once the ribosome has binded to the ER membrane?
It will detach from the ribosome, and disassociate from the SRP receptor
What is the process of a protein being released from the cell called?
Exocytosis
What is glycosilation of proteins and what does it do
The addition of a sugar to a protein
Acts as:
- Quality control
- Recognition
- Protection
Where does the sugar attach to the protein during glycosilation
On the asparagine side chain (C2H3NO)
In what direction is the protein read?
3’ -> 5’
What happens if a protein is correctly folded?
3 glucose are cleaved from the N-linked olgiosaccharide
What happens if a protein is uncorrectly folded?
Glucosyl transferase adds a single glucose back. Calnexin (membrane bound) then binds to the unfolded protein to prevent aggregation. From there glucosidase releases calnexin from protein to be reviewed and is let out of ER or will be refolded again
What happens to the protein if it is misfolded too many times?
Exits the ER through a protein translator complex, N linked olgiosaccharide is cleaved, and then moves through a proteasome to be degraded (in the cytosol)
What is the UPR?
The unfolded protein response is a response to the build up of misfolded proteins in the ER lumen.
1) inhibit protein synthesis
2) degrade all misfolded proteins
3) Increase transcription of chaperones (eg BiP, Calnexin and calreticulin)
What happens if the UPR does not succeed in resolving the number of proteins?
Apoptosis :(
What is the “pulse chase” experiment?
Originally created by George Emil Palade, it was an expiremtn that proved the theory of exocytosis
How many pathways are there in the cell?
3, exocytosis, endocytosis and retrieval pathways
Where do COPII coated vesicles come from?
The Endoplasmic reticulum
Where do COP I coated vesicles come from?
The Golgi
Where do clarithin coated vesicles come from?
From the plasma membrane
between Golgi and Endosomes
What happens with the Rab-GTP in membrane fusion?
binds to a rab effector
Once the Rab-GTP effector complex has been created? what happens next?
the v(esicle)-snare and t(arget)-snare create a complex. From there, the t(snare) disassociates from the vesicle and the vesicle forms with the target membrane
What happens to Rab-GTP once the vesicle has formed up with the membrane?
Rab-GTP disassociates from vesicle and is reduced, Rab-GDP then binds to GDI to keep it inactive
What side of the Golgi receives packages from the ER?
The cis face
What side of the golgi sends packages onwards?
The trans face
What is the function of the golgi
To further process the proteins and olgiosacharide chains
