Protein Trafficking Between Flashcards
The coat is key for efficient tethering and docking to the target membrane. True or false. Why?
False. The tethering and docking cannot take place if the coat is in the way
What are the members responsible for exocytosis?
The ER buds a COP2 vesicle, which only goes in the forward direction. The coated vesicle goes from
Cis Golgi to Trans Golgi and is transported to the plasma membrane.
What are the members responsible for endocytosis?
-Early endosome
-Late endosome
-Lysosome
-Essentially, the plasma membrane buds a clathrin coated vesicle to be delivered to an early endosome to a late endosome (cis to trans) then to a lysosome.
What is the fate of a vesicle in endocytosis?
It fuses with a lysosome
What is the proper sequence of compartments visited by proteins destined to be secreted from eukaryotic cells? (AKA exocytosis)
ER->Cis Golgi->Trans Golgi-> Plasma membrane via “post Golgi vesicle”
Neurofilament proteins (NF-L, NF-M, NF-H) are found primarily near the MTOC in neuronal cells, where they stabilize the organization of the endoplasmic reticulum and Golgi complex. True or false
True
Where are neurofilament proteins primarily found?
Near the MTOC in neuronal cells
What do neuronal filament proteins do?
They stabilize the organization of the endoplasmic reticulum and Golgi complex
COP II vesicles are the only ones that travel from the ER to the Golgi
True, they provide the only route of vesicular exit of the ER (only move in forward direction)
What is the regulatory mechanism of exocytosis?
Temporary storage in secretory granules until the cell is stimulated for exocytosis to occur.
Retrograde transport refers to movement of vesicles from ___ to ___.
Golgi to ER
How are vesicle exiting the endoplasmic reticulum formed?
COP II proteins select cargo and initiate budding from the ER and a scission protein cleaves the vesicle and reforms the ER.
How are vesicle exiting the endoplasmic reticulum formed?
COP II proteins select cargo and initiate budding from the ER and a scission protein cleaves the vesicle and reforms the ER.
What is the targeting signal used to retain resident Golgi proteins? (There are two)
Membrane spanning domain and flanking sequences
SNAREs are not used for tethering. True or false. Why
False. They are vital for tethering and docking
COP I vesicles not only provide transport from the Cis Golgi Network to the trans Golgi network, but also retrieve proteins with a KDEL sequence from VTCs or Golgi and return them to the ER. True or false. Why?
True, this is because they can retrograde and go forward.
The role of coat proteins in vesicle trafficking is to __.
Select the appropriate cargo to define the vesicle type, and they make it easier for the transport vesicle to form via direct and indirect binding.
Prior to fusion of a transport vesicle to its target membrane, what step has to happen?
Tethering and docking have to occur. Also, the vesicle needs to be released of its coat proteins so that it can begin to tether.
What controlls the tethering?
The RAB protein sequence
What controls the docking?
V-SNAREs interacting with T-SNAREs.
Retrograde transport from the Golgi complex to the ER occurs through ___ vesicles
COP I
What would a cell lacking functional T-SNAREs look like?
The transport vesicles would accumulate in the cytoplasm due to the inability to bind to the target membrane.
NSF unwinds the V-SNARE/T-SNARE complex to allow fusion during docking. True or false. Why?
False. While NSF does unwind the two complexes, it does this AFTER fusion has already occurred. The winding is necessary for the docking to occur in the first place.
What are the facilitating roles of SNARE proteins?
The function of SNARE proteins allows for docking to occurs they do this by winding together and bringing the two membranes closer together so they can fuse.
What is the specific role of NSF and SNAP in vesicle trafficking?
-NSF unwinds SNARE proteins after fusion (it hydrolyses ATP)
-SNAP winds the SNAREs together
During the process of vesicle fusion to the target membrane, where is ATP hydrolysis required?
ATP is required after fusion, where the SNAREs are unwound and separated.
What are common features of lysosomal hydrolases? Name 3
-only active at low PH levels to prevent accidental digestion
-involved in autocatalytic cleavage of pro enzyme
-uses M6P signal cleavage instead of receptors
What is the function of cytoplasmic HSC70 during endocytosis?
Removes the clathrin coat before docking occurs.
What is the function of adaptin proteins?
They link the plasma membrane to clathrin pitted coats.
Why do adaptin proteins exist?
This is because clathrin can’t bind to the membrane alone, it binds to receptors, and this binding is facilitated by adaptin proteins. They allow rapid internalization of receptors and ligands.
Clathrin binds to adaptor proteins that link clathrin to membrane proteins. True or false
True
What are retention signals for resident ER proteins?
They tell enzymes, which belong in certain locations in the ER, to go back to where they belong if needs be.
How do Retention signals work?
KDEL sequences (at C-Terminus) are recognized by the Cis Golgi Network, which triggers the formation of COP I vesicles returning the complex to the ER.
Which retention signal is responsible for transmembrane localization?
KKXX
What would happen if a cell failed to place mannose-6-phosphate on proteins?
This would prevent docking and fusion. M6P would not be recognized by receptors, the proteins would not be recognized, and they would fail to be delivered to late endosomes which would prevent lysosome fusion to occur.
List the 3 differences between lysosomes and endosomes
-Endosomes don’t contain degrading enzymes, while lysosomes do
-Lysosomes have a lower pH
-Lysosomes are more mature
What is the final destination of lysosomal proteins lacking the M6P tag?
They get secreted from the cell since the Golgi does not recognize them.
Explain how SNARE mediated vesicle fusion with target membrane
V-SNAREs interact with T-SNAREs and allow docking and fusion to occur.
Clathrin mediates the fusion of the vesicles with early endosomes. True or false.
True, it eventually is decoated before fusion.
Coated pits are formed from not wearing antiperspirant. True or false
False
Rab (Small GTPases) bound with GTP is critical for proper tethering of a vesicle/target organelle pair. True or false.
True
What is the trans-Golgi network?
It is the side of the Golgi that faces the plasma membrane, and it contains the most mature proteins and is responsible for sorting and distributing proteins to different places.
Explain how the retrieval signal, KDEL, mediates the rescue of resident ER proteins from the Golgi complex back to the ER.
It is recognized by Cis Golgi Network triggering COP I from the Golgi complex back to the ER.
Clathrin exhibits quaternary structure; defined by the assembly of theee heavy chains and three light chains to form a triskelion. True or False
True
