11.2 Membrane Dynamics Flashcards

1
Q

liquid-ordered (Lo) state

A

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

VDW- much stabilization energy
tightly packed

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2
Q

liquid-disordered (Ld) state

A

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

VDW not as stabilizing
more space to move

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3
Q

L0 to Ld transition can be caused by

A

heat which produces thermal motion of side chains

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4
Q

fatty acid composition affects

A

membrane fluidity

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5
Q

at physiological temperatures, long chain saturated fatty acids:

A

tend to pack into an Lo phase (more VDW)

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6
Q

at physiological temperatures, kinks in unsaturated fatty acids:

A

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

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7
Q

shorter-chain fatty acyl groups favor the

A

Ld state

less SA, less VDW

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8
Q

based on the amount of VDW, for packing:

A

increasing VDW favors ordered
decreasing VDW favors disordered

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9
Q

sterols have paradoxical effects on bilayer fluidity

A

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)

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10
Q

transbilayer movement of lipids requires

A

catalysis

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11
Q

transbilayer (“flip flop”)

A

movement has a large, positive free-energy change

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12
Q

membrane proteins facilitate the

A

translocation of individual lipid molecules

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13
Q

flippases

A

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)

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14
Q

floppases

A

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

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15
Q

scramblases

A

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

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16
Q

uncatalyzed transbilayer (“flip flop”) diffusion

A

is very slow

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17
Q

uncatalyzed lateral diffusion is

A

very fast

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18
Q

catalyzed transbilayer translocations

A

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

19
Q

phosphatidylinositol transfer proteins

A

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

20
Q

lipids and proteins diffuse ____ in the bilayer

A

laterally !

21
Q

individual lipid molecules undergo

A

Brownian movement

22
Q

FRAP

A

fluorescence recovery after photobleaching

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

23
Q

hop diffusion of individual lipid molecules

A

single particle tracking confirms lipid molecules diffuse laterally within small regions

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

24
Q

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

membrane proteins are limited in movement by:

A

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

slower, bigger

25
sphingolipids and cholesterol cluster together in
membrane rafts
26
microdomains (rafts)
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
27
protein rafts
proteins must have hydrophobic helical sections long enough to segregate into the thicker bilayer regions of rafts
28
lipid rafts are enriched in
1) proteins that have two long-chain saturated fatty acids covalently attached through Cys residues 2) GPI-anchored proteins
29
caveolae "Little caves"
specialized rafts have caveolin protein
30
caveolin
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*
31
membrane curvature and fusion are central to many biological processes
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
32
cardiolipin
can create or recognize membrane curvature -located in mitochondrial and bacterial membranes
33
protein-induced curvature of membranes
BAR domains
34
BAR domains
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
35
septins
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
36
fusion proteins
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
37
steps of fusion proteins
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*
38
SNARE proteins
snap receptors- family of proteins v-SNAREs t-SNAREs *very big in neurotransmitters
39
v-SNAREs
SNAREs in the cytoplasmic face of the intracellular vesicle
40
t-SNAREs
SNAREs in the target membrane with which the vesicle fuses
41
integrins
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
42
cadherins
involved in surface adhesion -undergo homophilic interacts with identical cadherins in an adjacent cell
43
selectins
have extracellular domains that bind specific polysaccharides on the surface of an adjacent cell -require calcium -essential part of the blood-clotting process