11.2 Membrane Dynamics

Question 1

liquid-ordered (Lo) state

Answer 1

gel-like state in which all types of motion of individual molecules are strongly constrained

VDW- much stabilization energy
tightly packed

Question 2

liquid-disordered (Ld) state

Answer 2

state in which individual hydrocarbon chains are in constant motion (lateral and rotational)

VDW not as stabilizing
more space to move

Question 3

L0 to Ld transition can be caused by

Answer 3

heat which produces thermal motion of side chains

Question 4

fatty acid composition affects

Answer 4

membrane fluidity

Question 5

at physiological temperatures, long chain saturated fatty acids:

Answer 5

tend to pack into an Lo phase (more VDW)

Question 6

at physiological temperatures, kinks in unsaturated fatty acids:

Answer 6

interfere with packing, favoring the Ld state (less VDW)

Question 7

shorter-chain fatty acyl groups favor the

Answer 7

Ld state

less SA, less VDW

Question 8

based on the amount of VDW, for packing:

Answer 8

increasing VDW favors ordered
decreasing VDW favors disordered

Question 9

sterols have paradoxical effects on bilayer fluidity

Answer 9

they interact with phospholipids containing unsaturated fatty acyl chains, compacting them and constraining their motion (ordered)

they associate with sphingolipids and phospholipids having long, saturated fatty acyl chains, making the bilayer fluid (disordered)

Question 10

transbilayer movement of lipids requires

Answer 10

catalysis

Question 11

transbilayer (“flip flop”)

Answer 11

movement has a large, positive free-energy change

Question 12

membrane proteins facilitate the

Answer 12

translocation of individual lipid molecules

Question 13

flippases

Answer 13

catalyze the translocation of the amino-phospholipids phosphatidylethanolamine (PE) and phosphatidylserine (PS) from the extracellular to the cytoplasmic leaflet of the plasma membrane

consume ~1 ATP per molecule of phospholipid translocated

related to the P-type ATPases (active transporters)

Question 14

floppases

Answer 14

move plasma membrane phospholipids and sterols from the cytoplasmic leaflet to the extracellular leaflet

are ATP-dependent
members of the ABC transporter family
each specializes in movement of specific lipids

Question 15

scramblases

Answer 15

move any membrane phospholipid across the bilayer down its concentration gradient

not dependent on ATP; some require Calcium
lead to controlled randomization of the head-group composition on the two faces of the bilayer – toward equilibrium

Question 16

uncatalyzed transbilayer (“flip flop”) diffusion

Answer 16

is very slow

Question 17

uncatalyzed lateral diffusion is

Answer 17

very fast

Question 18

catalyzed transbilayer translocations

Answer 18

flippase- outside in
floppase- inside out
scramblase- eiether or

Question 19

phosphatidylinositol transfer proteins

Answer 19

move phosphatidylinositol lipids across lipid bilayers
-believed to have roles in lipid signaling and membrane trafficking

Question 20

lipids and proteins diffuse ____ in the bilayer

Answer 20

laterally !

Question 21

individual lipid molecules undergo

Answer 21

Brownian movement

Question 22

FRAP

Answer 22

fluorescence recovery after photobleaching

rate is a measure of the rate of lateral diffusion of the lipids

Question 23

hop diffusion of individual lipid molecules

Answer 23

single particle tracking confirms lipid molecules diffuse laterally within small regions

movement from one region to another (“hop diffusion”) is rarer

Question 24

some membrane proteins are free to diffuse, whereas others are not

membrane proteins are limited in movement by:

Answer 24

-associating to form large aggregates (“patches”)
-anchoring to internal structures

slower, bigger

Question 25

sphingolipids and cholesterol cluster together in

Answer 25

membrane rafts

Question 26

microdomains (rafts)

Answer 26

clusters of cholesterol and sphingolipids that make the bilayer slightly thicker and more ordered than neighboring, phospholipid-rich regions
-can be up to 50% of the cell surface

Question 27

protein rafts

Answer 27

proteins must have hydrophobic helical sections long enough to segregate into the thicker bilayer regions of rafts

Question 28

lipid rafts are enriched in

Answer 28

1) proteins that have two long-chain saturated fatty acids covalently attached through Cys residues
2) GPI-anchored proteins

Question 29

caveolae “Little caves”

Answer 29

specialized rafts

have caveolin protein

Question 30

caveolin

Answer 30

integral protein that binds to the cytoplasmic leaflet of the plasma membrane
-forms dimers
-associates with cholesterol-rich membrane regions
-forces the bilayer to curve inward to form caveolae

protein that induces curvature, can increase lipid particles there, increases SA without changing the size of the cell

Question 31

membrane curvature and fusion are central to many biological processes

Answer 31

budding of vesicles from golgi complex
exocytosis
endocytosis
fusion of endosome and lysosome
viral infection
fusion of sperm and egg
fusion of small vacuoles (plants)
separation of two plasma membranes at cell division

Question 32

cardiolipin

Answer 32

can create or recognize membrane curvature
-located in mitochondrial and bacterial membranes

Question 33

protein-induced curvature of membranes

Answer 33

BAR domains

Question 34

BAR domains

Answer 34

domains consisting of coiled coils that form long, thin, curved dimers with a positively charged concave surface (interact w membrane)

BAR domain proteins assemble into crescent-shaped scaffolds and favor membrane curvature

Question 35

septins

Answer 35

family of GTP-binding proteins that polymerize at curved regions of the plasma membrane

-participate in cell division, exocytosis, phagocytosis, and apoptosis
-have an amphipathic helix that is important in vesicle `trafficking and neurotransmitter release

*increase curvature of PM

Question 36

fusion proteins

Answer 36

mediate specific fusion of two membranes by bringing about specific recognition and a transient local distortion of the bilayer structure

mediating fusion and not curvature*
*to get fusion, you need membranes close enough together

Question 37

steps of fusion proteins

Answer 37

1. 2 membranes recognize each other
2. bring membranes into close contact- remove water
3. bilayer becomes locally disrupted (hemi fusion)
4. bilayer fuses to form single continuous bilayer hydrophobic areas interact

Question 38

SNARE proteins

Answer 38

snap receptors- family of proteins
v-SNAREs
t-SNAREs

*very big in neurotransmitters

Question 39

v-SNAREs

Answer 39

SNAREs in the cytoplasmic face of the intracellular vesicle

Question 40

t-SNAREs

Answer 40

SNAREs in the target membrane with which the vesicle fuses

Question 41

integrins

Answer 41

surface adhesion proteins that mediate a cell’s interaction with the extracellular matrix and with other cells
-carry signals in both directions across the plasma membrane
-heterodimeric proteins composed of two unlike subunits, alpha and beta

Question 42

cadherins

Answer 42

involved in surface adhesion
-undergo homophilic interacts with identical cadherins in an adjacent cell

Question 43

selectins

Answer 43

have extracellular domains that bind specific polysaccharides on the surface of an adjacent cell
-require calcium
-essential part of the blood-clotting process