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Cell Molec > Biomembrane Structure > Flashcards

Biomembrane Structure Flashcards

1
Q

Lumen

A

fluid filled interior of organelle

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2
Q

What is the bilayer membrane composed of

A

phospholipids

hydrophobic tails and hydrophilic heads

proteins embedded in

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3
Q

Fluid Mosaic model

A

individual phospholipids can move laterally and spin within the plane of the membrane – causing the fluidity

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4
Q

What give membrane strength

A

non-covalent interactions between phospholipids and between phospholipids and proteins

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5
Q

Hydrophobic core helps with what

A

prevents unassisted movements of water soluble substances from one side to the other

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6
Q

what do integral proteins often form

A

dimers and higher order oligomers

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7
Q

How do peripheral proteins associate with membrane

A

non-covalent interactions with integral proteins or membrane lipids

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8
Q

How are lipid anchored proteins tethered

A

covalently attached hydrocarbon chain

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9
Q

What is the core of the bilayer

A

extremely hydrophobic

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10
Q

Why is the hydrophobic bilayer a good thing

A

prevents diffusion of anything hydrophilic across the membrane and very stable interactions (hydrophobic-van der waals) hold together

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11
Q

How did some organelles obtain double membrane

A

endosymbiont hypothesis

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12
Q

Exoplasmic faces

A

outside of cell

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13
Q

Cystolic faces

A

facing the cystol of the cell

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14
Q

three classes of lipids in the biomembrane

A

Phosphoglycerides , sphingolipids, sterols

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15
Q

what is the most abundant lipid in the membrane

A

phosphoglycerides

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16
Q

Structure of phosphoglycerides

A

glycerol 3-phosphate bound to: 2 fatty acid chains (16 or 18 carbon long) and one of many different head groups

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17
Q

Different Head groups

A

choline head-> phosphatidylcholine
phosphatidylethanolamine
phosphatidylserine
phosphatidyl-inositol

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18
Q

Sphingolipids structure

A

sphingosine molecule ( amino alcohol with a long fatty acid tail) bound to a long fatty acid chain and one of several head groups

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19
Q

Sphingomyelin

A

phosphocholine head group and is important in nerve cells

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20
Q

Glycolipids

A

have sugar head group
usually on leaflet facing outside
helps protect cell
not a phospholipid

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21
Q

Structure of sterols

A

4 carbon rings w hydrophilic hydroxyl group on 1 ring

very hydrophobic

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22
Q

Do sterols form membranes

A

NO

they wedge themselves between other membrane lipids

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23
Q

Sterol function

A

to regulate membrane fluidity

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24
Q

Most abundant sterol in membrane?

A

cholesterol

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25
Q

What contributes to fluid like consistency of the membrane

A 
phospholipids can move 
laterally 
spin in place (like a top) 
vibrate 
flip sides of the bilayer
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26
Q

How are lateral movements of phospholipids detected

A

FRAP

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27
Q

FRAP process

A
  1. label all molecules specific type membrane lipid with fluorescent dye
  2. shine laser on small patch of membrane, bleaching dye in that area
  3. measure how long takes labeled lipids to move into that spot (indicates rate of lateral movement
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28
Q

Factors Influencing membrane fluidity

A

1/ ratios of different types of lipids
2/ saturated v unsaturated phospholipids
3/ amount of cholesterol

29
Q

Ratios of different types of lipids

A

some phospholipids make membrane more fluid

dif organelles have dif ratio of lipids

30
Q

Saturated

A

all single bonds

31
Q

unsaturated

A

at least one double bond

32
Q

how does saturation affect membrane

A 
saturated= membrane tends to be rigid 
unsaturated= membrane are much more fluid
33
Q

Why does unsaturated fatty acid tails allow for more fluidity

A

put kinks in thus fatty acid tails cant pack as tightly

34
Q

How does cholesterol affect fluidity of membrane

A

inserts itself between fatty acid tails of bilayer

high concentration blocks phospholipids from moving laterally decreasing membrane fluidity

low concentration prevents phospholipid tails from packing in tightly thus increasing membrane fluidity

35
Q

Distribution of lipids in membrane

A

different leaflets of the bilayer have dif phospholipid compositions thus creating a difference in fluidity between two leaflets

36
Q

why is a dif in fluidity between the two leaflets important

A

membrane curvature

37
Q

lipid rafts

A

specific lipids grouped in patches in a single leaflet

38
Q

properties of lipid rafts

A

rich in cholesterol
resistant to detergent digestion
rich in protein which usually function to transmit a signal from outside of the cell to the inside (hormone- receptor)

39
Q

Which is thicker: sphingomyelin bilayer or phosphoglyceride?

A

sphingomyelin

40
Q

Effect of cholesterol on phosphoglyceride bilayer vs the sphingomyelin

A

on PC increases thickeness but does not affect thickness of SM

41
Q

Phospholipid shape of those with small head groups

A

conical

42
Q

PC on the exoplasmic leaflet and PE on the cystolic face causes what

A

natural curvature

43
Q

3 categories of membrane proteins

A

Integral, lipid anchored, peripheral proteins

44
Q

How are integral proteins anchored

A

some to the cytoskeleton

some just more freely laterally

45
Q

three domains of integral proteins

A

cytosolic, transmembrane, extracellular

46
Q

What do each of the integral protein domains contain

A

extracellular contains one or more sugar attached (glycoproteins)

Extracellular and cytoplasmic contain mostly hydrophilic amino acids

transmembrane hydrophobic amino acids

47
Q

Integral protein domains all consist of what

A

alpha helices or beta sheets

48
Q

Lipid anchored proteins

A

covalently bonded to lipid tail, lipid embeds itself into 1 leaflet of bilayer

49
Q

Peripheral membrane proteins

A

never interact with lipids, interacts with integral proteins or hydrophilic phospholipid head groups

50
Q

3 added lipid groups on lipid anchored proteins

A

Fatty acyl group
Prenyl group
GPI anchor

51
Q

What is a fatty acyl group

A

saturated fatty acid chain (14-16 carbons)

usually added to glycine or cysteine residue at beg or end of protein

52
Q

What is a prenyl group

A

chain of prenyl units attached to cysteine residue

53
Q

What is a GPI anchor

A

contains molecule of PI (two fatty acid tails are embedded in the membrane ), several sugar residues (outside of membrane), and ethanol amine (links to GPI anchor to the protein)

54
Q

What moves slower lipids or proteins along the membrane

A

proteins (10-20 times slower)

55
Q

Why do some membrane proteins not move

A

they have strong interactions with the cytoskeleton that underlies most membranes

56
Q

How to measure movement of proteins along the membrane

A

FRAP and cell fusion assays

57
Q

Cell fusion assays

A
  1. fuse human and mouse cell
  2. add mouse protein specific antibody, all the antibody label is
  3. time for protein movement, mouse protein seen dispersed
58
Q

Function of membrane proteins

A 
receptors (EX. bind to hormones) 
enzymes 
cell adhesions proteins 
transport 
cell recognition
59
Q

How are fatty acids synthesized

A

from acetyl CoA by water soluble enzymes and modified by elongation and desaturation in the ER

60
Q

What facilitates movement of fatty acids

A

small cytosolic proteins

61
Q

What moves phospholipids from one membrane leaflet to the opposite

A

flippases

62
Q

How is cholesterol synthesized

A

enzymes in the cytosol and ER membrane

63
Q

Fatty Acids are transported within cells by what

A

Fatty acid binding proteins

64
Q

Step 1 of phospholipid synthesis in ER membrane

A

2 fatty acids from actyl CoA esterified to phosphorylated glycerol backbone forming phosphatidic acid whose two long hydrocarbon chains anchor molecule to membrane

65
Q

Step 2 of phospholipid synthesis in ER membrane

A

phosphate converts phosphatidic acid into diacylglycerol

66
Q

Step 3 of phospholipid synthesis in ER membrane

A

polar head group transferred from cytosine diphosphocholine to the exposed hydroxyl group

67
Q

Step 4 of phospholipid synthesis in ER membrane

A

flippase proteins catalyze movement of phospholipids from the cytosolic leaflet in which that are initially formed to exoplasmic leaflet

68
Q

Methods of cholesterol and phospholipid transport between membrane

A

A: vesicles transfer lipids between membranes
B: lipid transfer is consequence of direct contact between membranes that is mediated by membrane embedded proteins
C: transfer is mediated by small soluble lipid transfer proteins

69
Q

synthesis of cholesterol

A

beta hydroxy beta methylglutaryl CoA converted to mevalonic acid by HMG-CoA

Mevalonate then converted to isopentenyl pyrophosphate which can then be converted to cholesterol

Cell Molec (5 decks)

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