Membrane trafficking

Question 1

Cell polarity

Answer 1

Differences at each end
(eg. apical and basolateral domain)

Question 2

What can polarized cells do or have?

Answer 2

1. they have different function at different cell regions
2. they define the inside v/s the outside
3. transmit signals from one end to the other

Question 3

What does membrane trafficking do?

Answer 3

Sends different proteins to different domains

Question 4

Two main types of membrane trafficking

Answer 4

1. exocytosis directly to target domain
2. exocytosis to any domain and then endocytosis followed by recycling to target domain

Question 4

Key concepts in secretory pathway

Answer 4

1. Some trafficking routes are polarized (ER to Golgi to PM)
2. Proteins are organized at sorting stating (trans golgi network)
3. Different routes are balanced by retrieval pathways (ER retrieval from golgi)

Question 5

What pathway is the default pathway?

Answer 5

Constitutive secretion

Question 6

What is NOT required for constitutive secretion?

Answer 6

Specific signals

Question 7

What do clathrin-coated vesicles do?

Answer 7

They can return the membrane to the Golgi, this shrinks the vesicle and makes cargo more concentrated.

Question 8

Regulated secretion

Answer 8

Here membranes are fully formed but only fuse with the plasmam membrane when a signal is recieved.

Question 9

Example of regulated secretion

Answer 9

Mast cell storing histamine

Question 10

Ways in which regulated secretion can deliver extra membrane material

Answer 10

1. cytokinesis
2. phagocytosis
3. plasma membrane repair

Question 11

3 options that endocytosed proteins have

Answer 11

1. recycling to the same domain of the plasma membrane
2. transcytosis to other domain of plasma membrane
3. degradation in the lysosome

Question 12

3 types of membrane changes during vesicle trafficking

Answer 12

1. vesicle forms from the donor membrane into the cytoplasm
2. vesicle fusion: vesicle merges with a target membrane
3. vesicle forms from a donor membrane away from the cytoplasm

Question 13

What coat can mediate vesicle formation into the cytoplasm?

Answer 13

Clathrin

Question 14

What helps vesicle fusion?

Answer 14

SNARES
Both t and v SNARES
they must be on opposite membrane

Question 15

ESCRT proteins

Answer 15

pinch
They form vesicles away from the cytoplasm (into the lumen or extracellular space)
Vesicle formation machinery is in the cytoplasm.

Question 16

Phosphoinositides

Answer 16

they label different membrane domains

Question 17

where are phosphoinositides found?

Answer 17

different PIPs are found at different subcellular locations

Question 18

Basic structure of PIP

Answer 18

inositol sugar, phosphate group (C1), glycerol and lipids

Question 19

Where can phosphoinositides phosphorylted?

Answer 19

They are always phosphorylated at C1 but they can also be phosphorylated at C 3,4 and 5.

Question 20

What are PIPS interconverted by?

Answer 20

PIP kinase (adds phosphate) and PIP phosphotase (removes phosphate)
Not all PIPs can be directly interconverted

Question 21

What proteins bind to PIP, cargo and clathrin

Answer 21

adaptor proteins

Question 22

which PIP targets clathrin coat assembly?

Answer 22

PI(4.5)P2

Question 23

RAB GTPAses

Answer 23

they are molecular switched that can direct vesicles
GEF exchanges GDP for GTP
GAP activates GTPase

Question 24

How do Rabs and PIPs combine to give membrane different identities?

Answer 24

1. Rab 5 GTP recruits PI 3 - kinase
2. PI3P can recruit RAB 5 GEF
3. More Rab 5 GEF makes more active Rab 5 GTP

Question 25

How do Rabs and PIPs combine to give membrane different identities? process

Answer 25

With a rab 5 GEF, rab 5 will release the GDP and bind to GTP, GDI leaves once this exchange happens, Rab 5 is on - lipid tether is exposed and it can insert into membrane.

Question 26

What work together in vesicle targetting and fusion?

Answer 26

Rabs and SNAREs