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

Lec 07: Membrane Structure Flashcards

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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
Q

What are three types of phosphoglycerides?

A

phosphatidyl- 1. ethanolamine 2. serine 3. choline

26
Q

What are sphingolipids based on?

A

sphingosine

27
Q

Most abundant membrane lipids in order:

A

phospholipids > glycolipids (and cholesterol)

28
Q

Glycolipid head group consists of?

A

sugar moiety

29
Q

3 types of glycolipid

A
  1. galactocerebroside 2. ganglioside 3. sialic acid (NANA)
30
Q

In animals, glycolipids are derived from?

A

spingosine

31
Q

In plants and bacteria, where are glycolipids synthesized from?

A

glycerol

32
Q

Where are glycolipids located?

A

on the cytosolic leaflet of plasma membrane facing AWAY from cytoplasm

33
Q

What interactions associate glycolipids with each other?

A
  1. van der walls between straight hydrocarbon chains 2. hydrogen bonds between sugars
34
Q

Cholesterol structure

A
  1. polar head group 2. rigid steroid ring structure (cholesterol stiffened) 3. nonpolar hydrocarbon tail (more fluid)
35
Q

How does cholesterol modulate properties of bilayer?

A
  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
Q

Phospholipid synthesis occurs?

A

cytosolic leaflet of plasma membrane

37
Q

How can phospholipids be distributed evenly across membranes?

A

Phospholipids rarely flip-flop The enzyme phospholipid translocator (flippase), uses ATP for the redistributing phospholipids across membrane leaflets (2um in a second)

38
Q

Cholesterol flip-flops ?

A

often

39
Q

Phospholipid rotate and diffuse?

A

rapidly

40
Q

At a certain temperature, membranes undergo ?

A

a phase transition -Liquid state frozen (gel-like) state

41
Q

The fluidity of the cell membrane influences?

A

-membrane transport -enzymatic reactions

42
Q

How is fluidity of cell membrane tightly regulated?

A

-Cells regulate the cell membrane composition by the synthesis of specific lipids (with specific fatty acids)

43
Q

Phase separation in artificial lipid bilayers occurs how?

A

spontaneously with certain lipid compositions (Giant liposomes)

44
Q

Giant liposomes ratio

A

1:1 (phosphatidylcholine, sphingomyeline) 1:1:1 - (phosphatidylcholine, sphigomyelin, cholesterol- large phase separated domains)

45
Q

Name: What are different lipid compositions lipid bilayers can form?

A
  1. lipid-lipid 2. lipid-protein 3. protein-protein 1. Lipid rafts 2. Lipid droplets 3. Lipid asymmetry
46
Q

Lipid raft

A

-Membrane proteins and lipids are concentrated in certain membrane areas in a temporary and dynamic fashion -usually not bigger than a few nanometers

47
Q

How do lipid rafts affect membrane thickness?

A

lipid rafts increase membrane thickness in region of lipid raft

48
Q

Lipid droplets store?

A

store neutral lipids (triacylglycerols, cholesterol esters)

49
Q

Lipid droplet structural composition

A

-surrounded by phospholipid monolayer -adipocytes contain giant lipid droplet

50
Q

lipid droplet associated proteins

A

-some functions in lipid metabolism, but function of protein majority unknown

51
Q

Lipid bilayer asymmetry created by?

A

flippases

52
Q

What is functional importance of lipid bilayer assymetry?

A

signal transduction –certain cytosolic proteins interact with SPECIFIC HEAD GROUPS (pkc binds to phosphatidylserine)

53
Q

Examples of mechanisms involving lipid asymmetry

A

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
Q

Glycolipid function

A

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
Q

Bilayer fluidity depends on?

A
  • fluidity depends on the composition (specific lipids) of the bilayer

Adv Cell Bio Quiz 02 (5 decks)

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