Class 12 - Transport From ER Through Golgi (PRETTY GOOD)

Question 1

ER exit site

Answer 1

Specialized regions of ER where COPII-coated transport vesicles destined for Golgi bud off.

Question 2

Exit signal

Answer 2

Present in ER transmembrane proteins to be recruited into vesicles. Recognized by adapter proteins of inner COPII coat.

Soluble cargo proteins in ER lumen also have exit signals, recognized by transmembrane proteins, which serve as cargo receptors.

Question 3

Homotypic fusion + 3 steps

Answer 3

The fusion of vesicle membranes from the same compartment.

1. NSF protein pries apart SNAREs.
2. Matching t and v-SNAREs on vesicles interact and force them together
3. Vesicles fuse, creating vesicular tubular clusters

Question 4

Heterotypic fusion

Answer 4

Vesicle fusion between membranes of different compartments.

Question 5

Vesicular tubular cluster

Answer 5

Structures formed when ER-derived vesicles fuse with one another. Function as transport containers that bring materials from ER to Golgi.

Bud off transport vesicles of their own - COPI-coated. Function as retrieval pathway, carrying proteins back to ER (escapees, receptors, SNAREs).

Move toward Golgi by means of motor proteins which walk along microtubules.

Question 6

Retrieval pathway

Answer 6

Between ER and Golgi: Done by COPI-coated vesicles which bud off from vesicular tubular clusters, carrying proteins back to ER.

Question 7

ER retrieval signal

Answer 7

Present in ER-residing proteins and bind to COPI coats, allowing their transport back to ER after escaping.

Question 8

KKXX sequence

Answer 8

An ER retrieval signal found at the C-terminus of ER membrane proteins (SNAREs, cargo receptors).

Allows them to enter the retrieval pathway back to ER.

Question 9

KDEL sequence

Answer 9

ER retrieval signal found in soluble ER resident proteins, such as BiP, at C-terminus.

Bind in Golgi - lower pH - and release in ER.

Question 10

KDEL receptor

Answer 10

Multipass transmembrane protein. Binds to KDEL sequence and packages any protein displaying it into COPI-coated retrograde transport vesicles (part of retrieval pathway).

Question 11

Cis face

Answer 11

The entry face of the Golgi.

Question 12

Trans face

Answer 12

The exit face of the Golgi.

Question 13

Cis Golgi network (CGN)

Answer 13

Collection of fused vesicular tubular clusters arriving from ER.

Proteins which don’t belong sent back to ER.

Question 14

Trans Golgi network (TGN)

Answer 14

Proteind are sorted and exported to lysosome, secretory vesicles, or plasma membrane.

Proteins not to be exported are returned to earlier compartment.

Question 15

Cis cisternae

Answer 15

First Golgi processing compartment.

Question 16

Medial cisternae

Answer 16

Second Golgi processing compartment.

Question 17

Trans cisternae

Answer 17

Final Golgi processing compartment, where glycosylation is completed.

Lumen of this is continuous with the TGN.

Question 18

Vesicle transport mechanism

Answer 18

Golgi cisternae are static compartments. Movements of cargo accomplished by forward-moving transport vesicles
(COPI), budding from one cisterna and fusing with the next.

Question 19

Cisternal maturation mechanism

Answer 19

Golgi is dynamic structure. Entire cisternae move through the stack. Vesicular tubular clusters from ER become cis-Golgi network, which mature to become medial and trans. Resident Golgi enzymes transported backwards as cisterna mature. Trans-cisterna disappears as vesicles bud off.

Question 20

GRASPs

Answer 20

Golgi matrix proteins called Golgi reassembly and stacking proteins. Form a scaffold between adjacent cisternae, giving Golgi stack structural integrity.

Question 21

Golgins

Answer 21

Golgi matrix proteins which form long tethers, composing a forest of tentacles that extend from the surface of the Golgi stack.

May contain binding sites for different Rab proteins; Initially select which part of Golgi stack transport vesicles engage with

Question 22

Golgi apparatus

Answer 22

Functions: Carbohydrate synthesis, makes all cell’s polysaccharides, sorting/dispatching station for ER products.

Structure: CGN and TGN sandwiching the cis, medial, and trans cisterna.

All resident proteins are membrane bound.

Question 23

Glycosylation in the Golgi

Answer 23

Takes place at membrane, in cis, medial, and trans cisternae.

Benefits:
1. Mark progression of protein folding for chaperones.
2. Participate in sorting in trans Golgi network
3. Keep other molecules at a distance—resistant to digestion or pathogens.
4. Cell-cell recognition
5. Signaling (Notch)

Question 24

Components of COPII vesicle (5)

Answer 24

1. Cargo from ER
2. Cargo receptors
3. Sar1 (GTPase)
4. Coat proteins
5. v-SNAREs

Question 25

2 ways to leave ER in COPII-coated vesicles

Answer 25

1. Selective - ER exit signal
2. Default - No ER exit signal

Question 26

How do cells respond to protein folding issues?

Answer 26

They make an excess of proteins to ensure enough fold up properly

Question 27

Reasons for glycosylation in Golgi

Answer 27

Protein folding, protein sorting, resistance to proteases, protection of cell, cell-cell recognition or adhesion, antigenic properties, regulatory roles