lecture 3: membrane dynamics

Question 1

what is the first step of vesicle budding?

Answer 1

• donor compartment forms a vesicle containing specific cargo

Question 2

what happens during vesicle budding?

Answer 2

• the vesicle pinches off from the donor membrane into the cytoplasm

Question 3

what is the final step in vesicle trafficking?

Answer 3

• vesicle recognizes and fuses with the correct target compartment

Question 4

typical vesicle diameter?

Answer 4

• ~60 nm

Question 5

which leaflet expands more to create positive curvature?

Answer 5

• outer leaflet (~1.5× more lipid than inner leaflet)

Question 6

what curvature is needed at the neck during fission?

Answer 6

negative curvature

Question 7

which enzyme flips lipids from outer → inner leaflet using atp?

Answer 7

• aminophospholipid translocator (flippase)

Question 8

which lipids are flipped inward by flippase?

Answer 8

pe and ps

phosphatidylethanolamine & phosphatidylserine

Question 9

which enzyme flips lipids from inner → outer leaflet using atp?

Answer 9

• abc transporter (floppase)

Question 10

which lipid shapes promote membrane curvature?

Answer 10

• inverted cone
• cylindrical
• cone

Question 11

examples of inverted-cone shaped lipids?

Answer 11

• lpc
• sphingomyelin

lysophosphatidylcholine

Question 12

examples of cylindrical lipids?

Answer 12

• pc
• ps

phosphatidylcholine, phosphatidylserine

Question 13

examples of cone-shaped lipids?

Answer 13

• pe

phosphatidylethanolamine

Question 14

can cholesterol move between monolayers spontaneously?

Answer 14

• yes

Question 15

what does phospholipase d produce and its shape?

Answer 15

• phosphatidate
• cone-shaped

Question 16

what does phospholipase c produce and its shape?

Answer 16

• DAG
• extremely cone-shaped

diacylglycerol

Question 17

what does phospholipase A produce and its shape?

Answer 17

• lysophospholipids
• inverted-cone shaped

Question 18

where are cone-shaped lipids located in budding vesicles?

Answer 18

• cytoplasmic side

Question 19

where are inverted-cone shaped lipids located?

Answer 19

• exoplasmic side

Question 20

what is preserved during vesicle budding & fusion?

Answer 20

• orientation of membrane leaflets and glycoproteins

Question 21

which lipids are mainly on the plasma membrane outer leaflet?

Answer 21

• pc
• sm
• glycolipids

phosphatidylcholines, sphingomyelin

Question 22

which lipids are mainly on the cytoplasmic leaflet?

Answer 22

• ps
• pe

phosphatidylserine, phosphatidylethanolamine

Question 23

functions of lipid asymmetry?

Answer 23

1. cell-cell interactions
2. protein recruitment
3. signalling

Question 24

typical lipid composition of plasma membrane?

Answer 24

• 25% pc
• 15% pe
• 30–40% cholesterol
• 10% sm
• 5% ps
• trace pi

Question 25

typical lipid composition of er?

Answer 25

* symmetric * 60% pc * 25% pe * 10% pi * trace ps

Question 26

lateral diffusion speed vs transverse flip-flop?

Answer 26

* lateral = very fast * transverse = very slow

Question 27

what do p-type atpases (flippases) do?

Answer 27

* flip pe/ps inward using atp * maintain lipid asymmetry

Question 28

floppases transport direction?

Answer 28

* inner → outer leaflet using atp

Question 29

example of a floppase transporter?

Answer 29

abcb1

Question 30

scramblase function?

Answer 30

* bidirectional * energy-independent lipid equilibration

Question 31

what activates tmem16f scramblase?

Answer 31

* high ca²⁺

Question 32

why does scramblase temporarily inactivate flippases?

Answer 32

* to expose ps on outer leaflet during signalling

Question 33

where are glycerophospholipids + ceramide synthesised?

Answer 33

* er

Question 34

where are sphingomyelin & glycolipids synthesised?

Answer 34

* golgi (post-golgi synthesis)

Question 35

what does “enriched at pm” mean?

Answer 35

* higher concentration at plasma membrane than er/golgi

Question 36

cholesterol synthesis site?

Answer 36

* er, increases along secretory pathway

Question 37

two mechanisms of lipid transport between organelles?

Answer 37

* vesicular transport * lipid transfer proteins (ltp)

Question 38

example of ltp? | lipid transfer proteins (ltp)

Answer 38

* tulip (tubular lipid binding domain protein)

Question 39

what is a lipid raft?

Answer 39

* cholesterol & sphingolipid-rich microdomain in plasma membrane

Question 40

lipid rafts physical properties?

Answer 40

* more ordered/rigid than surrounding membrane * thicker bilayer

Question 41

which lipids are enriched in rafts?

Answer 41

1. sphingomyelin 2. glycolipids 3. cholesterol

Question 42

which lipids are depleted in rafts?

Answer 42

* pc

Question 43

what happens if cholesterol is depleted?

Answer 43

* rafts are disrupted

Question 44

# lipid rafts umbrella hypothesis?

Answer 44

* neighbouring lipid headgroups shield cholesterol from water

Question 45

how can lipid rafts be detected experimentally?

Answer 45

* frap (fluorescence recovery after photobleaching)

Question 46

what does slow diffusion in frap indicate? | frap (fluorescence recovery after photobleaching)

Answer 46

* protein/lipid likely in raft (more ordered, rigid)