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Adv Cell Bio Quiz 02 > Lec 07: Membrane Structure > Flashcards

Lec 07: Membrane Structure Flashcards

1
Q

Lipid bilayers are mostly composed of?

A

-50% mass from lipids -50% proteins

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2
Q

How many lipids are present per protein? Why?

A

Since proteins are large molecules, ~50 lipids/ protein

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3
Q

Are lipid membranes amphiphilic?

A

lipid membranes are amphiphilic (hydrophilic head and hydrophobic tail)

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4
Q

How are all lipids in membrane bilayer amphiphilic?

A

hydrophilic head, hydrophobic tail

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5
Q

Hydrophilic head polarity / charge

A

polar or charged

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6
Q

Polarity of hydrophobic tails?

A

Nonpolar

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7
Q

The geometry of lipids influences what?

A

packing architecture (micelles or lipid bilayer) when mixed with water

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8
Q

Micelle shape

A

Cones form Micelles in water

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9
Q

Lipid bilayer shape

A

cylindrical tube forms lipid bilayer in water

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10
Q

Micelles of ____ molecules are thought to be irregular?

A

amphillic molecules

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11
Q

Why are lipid bilayer edges energetically unfavorable?

A

Tears in the membrane expose edges of Planar phospholipid bilayer exposed to water

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12
Q

How can lipid bilayer edges become energetically favorable?

A

Sealed compartment formed by phospholipid bilayer

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13
Q

How can tears in the membrane be beneficial for biological system?

A

A tear leads to rearrangement of lipids which seals the tear

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14
Q

Liposomes

A

synthetic phospholipid vesicles

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15
Q

Why do liposomes and vesicles not fuse spontaneously?

A

1) water molecules bind to hydration shell 2) hydration shell protects integrity of membrane-enclosed organelles 3) membrane fusion enzymes squeeze membranes into proximity that displaces H2O bound to headgroups 4) this leads to fusion

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16
Q

Define hydration shell

A

polar/charged headgroups

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17
Q

Hydration shell function?

A

protect integrity of membrane-enclosed organelles

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18
Q

What kind of bonds are between fatty acid chains?

A

unspecific Van der Waals attractive forces between fatty acid chains

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19
Q

How can lipid motion in a lipid bilayer be modeled?

A

in silico, in vitro, in vivo

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20
Q

What are the 4 motions in which lipids can move in a lipid bilayer?

A
  1. lateral diffusion 2. flexion 3. rotation 4. flip-flop (rare)
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21
Q

How can single labeled lipids be followed in real time?

A
  1. fluorescent label- lateral diffusion 2. spin label (NO-group) - flip flop
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22
Q

What do archaea lipids contain ?

A

prenyl chains instead of fatty acid chains

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23
Q

Phospholipids contain?

A
  1. charged or polar head 2. nonpolar hydrocarbon tails (saturated or non-saturated)
24
Q

What are two subfamilies of phospholipids?

A

1) phosphoglycerides 2) sphingolipids

25
What are three types of phosphoglycerides?
phosphatidyl- 1. ethanolamine 2. serine 3. choline
26
What are sphingolipids based on?
sphingosine
27
Most abundant membrane lipids in order:
phospholipids \> glycolipids (and cholesterol)
28
Glycolipid head group consists of?
sugar moiety
29
3 types of glycolipid
1. galactocerebroside 2. ganglioside 3. sialic acid (NANA)
30
In animals, glycolipids are derived from?
spingosine
31
In plants and bacteria, where are glycolipids synthesized from?
glycerol
32
Where are glycolipids located?
on the cytosolic leaflet of plasma membrane facing AWAY from cytoplasm
33
What interactions associate glycolipids with each other?
1. van der walls between straight hydrocarbon chains 2. hydrogen bonds between sugars
34
Cholesterol structure
1. polar head group 2. rigid steroid ring structure (cholesterol stiffened) 3. nonpolar hydrocarbon tail (more fluid)
35
How does cholesterol modulate properties of bilayer?
1. enhance permeability barrier 2. makes membrane less deformable 3. prevents membrane from freezing (despite high concentrations) 4. cholesterol does not make membranes less fluid
36
Phospholipid synthesis occurs?
cytosolic leaflet of plasma membrane
37
How can phospholipids be distributed evenly across membranes?
Phospholipids rarely flip-flop The enzyme phospholipid translocator (flippase), uses ATP for the redistributing phospholipids across membrane leaflets (2um in a second)
38
Cholesterol flip-flops ?
often
39
Phospholipid rotate and diffuse?
rapidly
40
At a certain temperature, membranes undergo ?
a phase transition -Liquid state frozen (gel-like) state
41
The fluidity of the cell membrane influences?
-membrane transport -enzymatic reactions
42
How is fluidity of cell membrane tightly regulated?
-Cells regulate the cell membrane composition by the synthesis of specific lipids (with specific fatty acids)
43
Phase separation in artificial lipid bilayers occurs how?
spontaneously with certain lipid compositions (Giant liposomes)
44
Giant liposomes ratio
1:1 (phosphatidylcholine, sphingomyeline) 1:1:1 - (phosphatidylcholine, sphigomyelin, cholesterol- large phase separated domains)
45
Name: What are different lipid compositions lipid bilayers can form?
1. lipid-lipid 2. lipid-protein 3. protein-protein 1. Lipid rafts 2. Lipid droplets 3. Lipid asymmetry
46
Lipid raft
-Membrane proteins and lipids are concentrated in certain membrane areas in a temporary and dynamic fashion -usually not bigger than a few nanometers
47
How do lipid rafts affect membrane thickness?
lipid rafts increase membrane thickness in region of lipid raft
48
Lipid droplets store?
store neutral lipids (triacylglycerols, cholesterol esters)
49
Lipid droplet structural composition
-surrounded by phospholipid monolayer -adipocytes contain giant lipid droplet
50
lipid droplet associated proteins
-some functions in lipid metabolism, but function of protein majority unknown
51
Lipid bilayer asymmetry created by?
flippases
52
What is functional importance of lipid bilayer assymetry?
signal transduction --certain cytosolic proteins interact with SPECIFIC HEAD GROUPS (pkc binds to phosphatidylserine)
53
Examples of mechanisms involving lipid asymmetry
**1.) Certain cytosolic protein interactions with SPECIFIC HEAD GROUPS** Example: pkc binds to phosphatidylserine **2.) Phosphatidylinositol can be phosphorylated** Example: PI-3-kinase phosphorylates PI and there by recruits cytosolic proteins **3.) Extracellular signal can induce cleavage of phospholipids on cytosolic site** Example: Phospholipase C cleaves of polar head group, generating second messangers **4.) Distinguishing between live and dead** Example: Phosphatidylserine atypically shows up on the extracellular membrane site in apoptotic cells
54
Glycolipid function
**1-associate with each other and incorporate into lipid rafts** **2-function in cell recognition processes/ cell interaction of with surroundings** --Lectins bind to glycolipids (and glycoproteins) **3-protect the membrane from harsh conditions** (glycocalyx i.e. low pH, digestion enzymes etc) **4-influence electrical fields and interact with Ca2+ ions** **5-can be hijacked by pathogens to enter cells** -- Cholera toxin and polyomaviruses use GM1 as entry receptor
55
Bilayer fluidity depends on?
- fluidity depends on the composition (specific lipids) of the bilayer

Adv Cell Bio Quiz 02 (5 decks)

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