Protein Trafficking 2

Question 1

ER targeting sequence

Answer 1

hydrophobic signal sequence at N terminus

Question 2

SRP

Answer 2

signal recognition particle

ribonucleoprotein (of RNA + protein) complex

Question 3

How does ER targeting work

Answer 3

When signal sequence emerges from ribosome, recognised by SRP and binding of SRP to signal sequence stops translation
The complex (chain/ribosome/SRP) can bind to ER membrane which has SRP receptor. This guides the complex to the translocon.
SRP an SRP receptor hydrolyse their GTP and change conform- SRP released from complex and SRP receptor can be recycled
Extension of PP chain pushes chain through ER membrane into lumen.
Unfolded in the process

Question 4

translocon

Answer 4

protein conducting channel

Question 5

Lumenal proteins

Answer 5

assist translocation
For proteins soluble in ER lumen or ER derived organelles and secreted proteins the signal sequence is cleaved (by a lumenally located signal peptidase protein complex), creating a new N terminus

Question 6

Transmembrane protein

Answer 6

For simple (Type II) membrane proteins the signal sequence is not cleaved and remains transmembrane

Question 7

Anchor sequences

Answer 7

non-cleavable signal sequences

Have longer stretches of AAs and no signal peptidase cleavage sequence.

Question 8

All membrane proteins situated in the endomembrane system (ER, golgi etc)..

Answer 8

are assembled in the ER and then trafficked to other locations
Same said for lumenal proteins in these organelles and secreted proteins

Question 9

what happens once ribosomes on the ER have finished translating the ER targeted protein

Answer 9

falls of ER and binds to another mRNA. This may or may not code for another ER protein

Question 10

Anterograde transport

Answer 10

ER to golgi to plasma mem

Question 11

Retrograde transport

Answer 11

Golgi to ER etc

Question 12

General mechanism of how molecules move between organelles using budding and fusion

Answer 12

1. Vesicle buds from donor compartment
2. Pinches off and translocates from donor to acceptor compartment
3. Vesicle docks with acceptor compartment
4. Fuses, releasing contents into lumen

Question 13

Clathrin coats

Answer 13

help buds form, assemble onto membranes
Assembled from clathrin proteins and adaptor proteins
Can assemble on membranes into ‘cages’
Final ‘scission’ event carried out by protein dyamin

Question 14

Coats made from proteins other than clathrin

Answer 14

Different coats involved in different trafficking events: clathrin involved in budding from the plasma membrane and TGN (trans golgi network)
COPII coats are involved in anterograde transport from the ER. COPI coats are involved in retrograde transport from Golgi apparatus.

Question 15

CLathrin-coated vesicle (clathrin +adaptin 1 proteins)

Answer 15

Origin golgi
destination lysosome (via endosomes)

Question 16

Clathrin coated (clathrin +adaptin 2)

Answer 16

origin plasma mem

destination endosomes

Question 17

COP coated (COP proteins)

Answer 17

ER, golgi origin and golgi, ER destination