COPII
What is the starting location and destination of COPII coats?
Starting at the ER and destination is the Golgi
What is the starting location and destination of COPI coats?
Starting at the Golgi and destination is the ER
Leaflet OUTSIDE the cell.
What is the unfolded protein response (UPR)?
When there are too many unfolded proteins in the ER, the UPR is triggered to activate more chaperones and increase the folding capacity of the ER.
What side of the organelle is the exit signal on the cargo receptor and what side is the exit signal for the soluble cargo protein?
Cytosol, ER lumen
What does Sar1 do?
Assembles the COPII coat at the ER membrane
What is the Golgi apparatus (structurally)?
What is the difference between constitutive and regulated exocytosis (cell type and how often it happens)?
Constitutive exocytosis is continuous and in all cells to supply lipids to the plasma membrane and secrete proteins. Regulated exocytosis is in cells that specialize in secretion and occurs in response to an extracellular signal.
What is the trend of pH of the organelles in the cell? What is the most acidic and basic organelle?
Increasing acidity in the direction of protein travel. Most acidic is lysosome and most basic is mitochondria.
What are exit signals and what are they recognized by?
Amino acid sequence, recognized by inner coat proteins
What are the 3 functions of adaptor proteins?
Select and concentrate cargo, deform ER membrane, and recruit outer coat proteins (COPII) to form a bud
What is the function of the Golgi and what determines directionality of the cisternae?
The Golgi modifies proteins to help them with their function. The cis face is towards the ER (receives) and trans face is the output.
What side does the inner leaflet face?
Lumen
COPII binds at higher pH and releases at lower pH. COPI binds at lower pH and releases at higher pH.
What is the function(s) of the inner coat (two functions) and outer coat (1 function)?
The inner coat selects and concentrates cargo at the site of vesicle formation and recruits outer coat proteins. The outer coat deforms the membrane and shapes the vesicle.
Where are Sar-1 GEF and Sar-1 GTP and what do they do?
Sar-1 GEF is localized to the ER membrane and regulates Sar-1 activity. Sar-1 GTP recruits COPII adaptor proteins at the surface of the membrane.
What is a KDEL and what does it do?
ER retrieval signal found on ER resident proteins, indicates for proteins to be retrieved from the Golgi.
What are the 5 components of the endomembrane system?
ER, Golgi, Endosomes, Lysosomes, Cell membrane
Describe the 2 models of protein transport through the Golgi and which is more accurate.
The vesicle transport model says that cisternae are fixed and retain their resident proteins, proteins are transported from cis to medial to trans cisternae via transport vesicles. The cisternal maturation model says cisternae are dynamic and acquire/lose specific Golgi resident proteins and matures from cis to medial to trans (cargo doesn't leave).
Cisternal maturation model is more correct.
What are the 2 destinations of membrane bound proteins with exit signals?
Membrane of another organelle in the endomembrane system OR cargo receptor that is recycled back to the ER
What is the shape and property of the unique structure on Sar-1, what does it do, and what happens when it interacts with Sar-1 GEF?
Amphiphilic helix, it interacts with Sar1-GEF to exchange GDP for GTP and expose the helix which embeds in the ER membrane.
What happens when ER retrieval signals bind to KDEL receptors in the Golgi membrane?
The protein gets packaged into COPI coated vesicles, buds off the Golgi, and returns to the ER.
What do the Rab tethers and SNARES do?
Rab tethers are Rab proteins on the cargo that bind tethering proteins on the target membrane. vSNAREs on the vesicle interact with tSNARES on the target membrane to undergo a conformational change as the membranes come into contact.
Describe the experiment testing the vesicle transport and cisternal maturation model. What was the main takeaway?
They used yeast which have separated cisternae and watched a single cisternae over time tagging the cis proteins green and trans proteins red. They saw that over time the green cisternae became red. The main takeaway is that the cisternal maturation model is more accurate and Golgi resident proteins are lost and gained from the cisternae as it matures.
What is the difference between soluble and membrane protein exit signals and their interactions?
Soluble proteins must bind cargo receptors with the exit signal and membrane proteins directly interact with inner coat proteins.