Protein Trafficking

Question 1

What pathway do eukaryotes use for synthesising and sorting secreted proteins?

Answer 1

secretory

Question 2

What are the 3 basic steps of protein secretion?

Answer 2

• protein synthesis + translocated across ER
• protein folding in ER
• Protein transport to golgi

Question 3

What part of the cell is responsible for sending out proteins to the correct place in/out of the cell?

Answer 3

ER

Question 4

What is the SRP?

Answer 4

Signal recognition particle

Question 5

Co-translational translocation
Signal sequence on mRNA is transcribed/translated. The signal sequence is bound by ___ which targets the _____ to the SRP-receptor which requires ____. Opening the translocon inserts the signal sequence, and GTP _____ release the signal sequence. The signal sequence is cleaved by a membrane-bound ______ enzyme. The polypeptide is elongated in the __-terminal to __-terminal direction. The protein is released into the __ _____ and the ribosome is released into the _______

Answer 5

translated
SRP
ribosome
GTP
hydrolysis
peptidase
N
C
ER lumen
cytosol

Question 6

Inserting proteins into membranes
The ribosome attaches to the translocon on the __ membrane, and the protein is transcribed/translated until a hydrophilic/hydrophobic stretch is generated and a membrane stop-transfer-anchor sequence is identified. The hydrophobic stretch is left in/out the membrane. The translocon moves laterally and _____ the protein. The rest of the protein is generated and the complex dissociates/asssociates

Answer 6

ER
translated
hydrophobic
in
ejects
dissociates

Question 7

What does a hydrophobic membrane domain act as?

Answer 7

A stop transfer signal and leaves the protein inserted in the ER membrane

Question 8

What is the secretory pathway used for?

Answer 8

To send proteins out of the cell or to membranes

Question 9

Secretory Pathway
Proteins are translated/translocated into the ___ lumen for folding and glycosylation. The vesicles fuse together to form the __-____, and proteins can be sent back to ER via _______ vesicles. Transport from the golgi to the __ is via ______ vesicles, and transfer through the golgi is via ______ maturation. The TGN sends proteins to the lysosomes. Vesicles coming into the cell are sent to the lysosome where the contents will be either _______ or sent back via the TGN to the cell ______

Answer 9

translocated
ER
cis-golgi
retrograde
ER
retrograde
cisternal
degraded
membrane

Question 10

How do vesicles work?

Answer 10

They bud-off from one membrane and fuse with another

Question 11

Proteins that are integrated into a vesicle membrane keep the same _______ to the cytosol

Answer 11

orientation

Question 12

List the 3 types of vesicles

Answer 12

COP I
COP II
Clathrin-coated

Question 13

Where do COP I vesicle transport proteins to?

Answer 13

transport proteins in a retrograde direction between golgi and ER

Question 14

Where do COP II vesicle transport proteins to?

Answer 14

Transport proteins from rough ER to golgi

Question 15

Where do Clathrin-coated vesicle transport proteins to?

Answer 15

transport proteins from the plasma membrane to endosomes

Question 16

What is meant by the term retrograde?

Answer 16

moves in the reverse direction

Question 17

Vesicle budding
- Initiated by ___-binding proteins to cell membrane causing _________. Coat proteins in the ______ bind to membrane ____ receptors. cargo proteins are recruited into the budding vesicle and the membranes ____ freeing the _______. The coat proteins are lost and _______

Answer 17

GTP
invagination
cytosol
cargo
fuse
vesicle
recycled

Question 18

Vesicle docking
- A vesicle will ____ to a target membrane vie the interaction of ____ proteins. The SNARE proteins are in pairs ensuring that the vesicle fuses with the correct ______

Answer 18

fuse
SNARE
membrane

Question 19

What are t-SNAREs?

Answer 19

target membrane SNARE

Question 20

What are v-SNAREs?

Answer 20

vesicle SNARES

Question 21

What receptor carries out the retrieval of ER proteins from the golgi?

Answer 21

KDEL receptor

Question 22

KDEL receptor
-ER luminal proteins are incorporated into COP__ vesicles and transported into the ____. ER resident proteins have a __-terminal KDEL signalling sequence (Lys-___-___-____. COP __ transport these proteins back to the ER and the KDEL receptor binds proteins with KDEL sequence.

Answer 22

II
gogli
C
Lys-Asp-Glu-Leu

Question 23

The affinity of the KDEL receptor is higher/lower at low pH as in the golgi, but much lower/higher at high pH as in the ER

Answer 23

higher

lower

Question 24

What is the endocytotic pathway used for?

Answer 24

To bring proteins into the cell across the plasma membrane