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ESA 2- Membranes and Receptors > The Membrane Bilayer > Flashcards

The Membrane Bilayer Flashcards

1
Q

What are the general functions of biological membranes?

A

Continuous, highly selective permeability barrier, Control of enclosed chemical environment, Communication, Recognition, Signal generation in response to stimuli

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2
Q

What do biological membranes capture?

A

An area of solute

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3
Q

Why are biological membranes needed for communication?

A

Needed to control flow of information between cells and their environment

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4
Q

Between where do biological membranes control communication?

A

Can be outside the cell, or outside of an organelle

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5
Q

What do biological membranes need for communication?

A

Mechanisms to communicate with outside environment

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6
Q

What do membranes recognise?

A

Signalling molecules
Adhesion proteins
Immune cells

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7
Q

What do adhesion proteins allow?

A

Cells to recognise each other

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8
Q

What stimuli do membrane generate signals in response to?

A

Electrical

Chemical

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9
Q

What do different regions of the plasma membrane have?

A

May have different functions

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10
Q

What functions can different regions of the plasma membrane have?

A 
Interaction with basement membrane
 Interaction with adjacent cells
 Absorption of body fluids
 Secretion
 Transport
 Synapses
 Electrical signal conduction
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11
Q

Why is absorption of body fluids important?

A

Provides nutrients for cell growth

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12
Q

Why is it important that cells are able to transport themselves?

A

Can allow to look for nutrients to bring into the cell

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13
Q

What are the mechanisms in a synapse membrane specialised to do?

A

Release neurotransmitter

Have receptors to recognise neurotransmitters

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14
Q

What is needed for electrical signal conduction?

A

Proteins allow an action potential to be conducted along axon

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15
Q

What have a change in shape of membrane result in?

A

A change in properties of a different region

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16
Q

Why is the plasma membrane ever changing?

A

So it’s suited to the needs of the function that it’s doing in any one part of the cell

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17
Q

What do different membranes have?

A

Specialised function

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18
Q

Give an example of a membrane with a specialised function

A

The mitochondrial membrane- specialised for energy conservation by oxidative phosphorylation

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19
Q

What does membrane composition vary depends upon?

A

The source of the membrane

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20
Q

Generally, what is the membrane composition when dry?

A

40% lipid
60% protein
1-10% carbohydrate

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21
Q

What % of the membranes total weight is water?

A

20%

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22
Q

Why is water needed in membranes?

A

To make hydrophilic interactions

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23
Q

Why are hydrophilic interactions in membranes important?

A

To keep the bilayer organised

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24
Q

What kind of molecules are membrane lipids?

A

Amphipathic

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25
Q

What is meant by amphipathic?

A

Contain both hydrophilic and hydrophobic moiety

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26
Q

What does the distribution of membrane lipids vary depending on?

A

Cell type- it is tissue specific

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27
Q

What is the distribution of membrane lipids related to?

A

Function

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28
Q

What are the predominant lipids in membranes?

A

Phospholipids

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29
Q

What are phospholipids made up of?

A

Glycerol backbone

Two fatty acid chains

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30
Q

Are the two fatty acid chains in phospholipids the same?

A

They can be different fatty acids, with different numbers of C’s

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31
Q

How many C’s do the fatty acids in phospholipids have?

A

Beween C14 and C24

C16 and C18 most prevalent

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32
Q

What is the importance of the C16 and C18 prevalence?

A

It means that the thickness of the membrane is always about the same, as the fatty acid chains always about the same length

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33
Q

What does a cis double bond in a fatty acid chain introduce?

A

A kink

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34
Q

Where is sphingomyelin found?

A

In membranes

35
Q

Why is sphingomyelin unique?

A

It is the only phospholipid based on glycerol

36
Q

What are glycolipids?

A

When the phosphate head group is replaced with a sugar

37
Q

What is a cerebroside?

A

A glycolipid with a single sugar residue

38
Q

What is a ganglioside?

A

A glycolipid with an oligosaccharide is attached

39
Q

In what ways are all membrane lipids similar?

A

Have a long aliphatic chains and a small head group

40
Q

What is the importance of all membrane lipids being similar?

A

Keeps membrane thickness about the same

41
Q

When is it important that membrane thickness is kept about the same?

A

When proteins are added to the membrane

42
Q

What is a lipid micelle?

A

A sphere formed when hydrophobic tails clump together on the inside, and hydrophilic heads face outwards forming hydrogen bonds with water

43
Q

What is a lipid bilayer?

A

Double sheet

44
Q

How are lipid bilayers form?

A

When hydrophilic heads face outwards on either side, bringing the hydrophobic tails together

45
Q

Do phospholipids more naturally form bilayers or micelles?

A

Bilayers

46
Q

What are bilayers able to do?

A

Enclose a space

47
Q

How can lipid bilayers be clinically useful?

A

In drug delivery

48
Q

How can lipid bilayers be used in drug delivery?

A

The drug can be enclosed in the space formed by the bilayer, and proteins can be added into the membrane that targets the drug to the tissues

49
Q

What is the lipid bilayer the favoured structure for?

A

Glycolipids in aqueous media

50
Q

When is bilayer formation spontaneous?

A

In water

51
Q

What is bilayer formation in water driven by?

A

The van der Waals attractive forces between the hydrophobic tails

52
Q

What is the bilayer structure stabilised by?

A

Non-covalent forces

53
Q

What non-covalent forces stabilise the bilayer structure?

A

Electrostatic
Hydrogen bonding
Interactions between hydrophilic groups and water

54
Q

What is the permeability of pure lipid bilayers?

A

Very low to ions and most polar molecules

55
Q

What are the methods of phospholipid motion?

A

Flexion
Fast axial rotation
Fast lateral diffusion
Flip-flop

56
Q

What is flexion?

A

Intra-chain motion

57
Q

What causes flexion?

A

Kink formation in fatty acyl chains

58
Q

Where does fast lateral diffusion occur?

A

Within the plane of the bilayer

59
Q

How common is flip-flop?

A

Rare

60
Q

What is flip-flop?

A

Movement of lipid molecules from one half of the bilayer to another on a one-for-one exchange basis

61
Q

Why is flip-flop rare?

A

Because its thermodynamically unfavourable

62
Q

Why is flip-flop thermodynamically unfavourable?

A

Because have to take a hydrophilic group through a hydrophobic domain

63
Q

What kind of bonds influence the bilayer structure?

A

Cis double bonds

64
Q

What effect do unsaturated hydrocarbon chains with cis double bonds have?

A

Reduces phospholipid packing

65
Q

What does the reduction in phospholipid packing lead to?

A

Disruption of hexagonal packing of phospholipids

66
Q

What is the result of the disruption of phospholipid packing?

A

Membrane is more dynamic/flui

67
Q

Why do we need polyunsaturated fats in the diet?

A

Because the body can’t produce them, but they are needed to keep membranes dynamic

68
Q

What is cholesterol?

A

A plasma membrane lipid

69
Q

What % of total membrane lipid does cholesterol make up?

A

45%

70
Q

What kind of head group does cholesterol have?

A

Polar, hydrophilic

71
Q

What structure does cholesterol have?

A

Rigid, planar, steroid ring structure

72
Q

What kind of C-C bonds are present in cholesterol?

A

Largely single

73
Q

What is the result of cholesterols structure?

A

It is very rigid

74
Q

What does cholesterol abolish?

A

The endothermic phase transition of phospholipid membrane

75
Q

What causes the endothermic phase transition?

A

Usually, a large amount of energy is needed for a phospholipid to change from semi-crystalline arrangement to fluid membrane

76
Q

How does cholesterol remove/reduce the need for the endothermic phase transition?

A

It means the membrane doesn’t suddenly become fluid, so there is a gradual change

77
Q

What brings cholesterol into the phospholipid bilayer?

A

The ß-OH group hydrogen bonds with the C=O group on the phospholipid

78
Q

Does does bringing in of cholesterol bring into the membrane?

A

The rigid structure, which grafts onto phospholipid

79
Q

What is the effect of the grafting of the rigid structure of cholesterol onto phospholipid?

A

Motion restricted in phospholipid adjacent to the rigid steroid ring of cholesterol.
Motion unaffected in phospholipid adjacent to flexible tail of cholesterol

80
Q

What is it said of the effects of cholesterol on the phospholipid bilayer?

A

They are paradoxical

81
Q

Why are the effects of cholesterol in the lipid bilayer paradoxical?

A

Reduced phospholipid chain motion leads to reduced fluidity

Reduced phospholipid packing leads to increased fluidity

82
Q

What is the result of the paradoxical effects of cholesterol?

A

As soon as the membrane starts to move away from the standard properties in either direction, cholesterol buffers it

83
Q

What functions of membranes do proteins carry out?

A 
Enzymes
 Transporters
 Pumps
 Ion channels
 Receptors
 Energy transducers
84
Q

What is the protein content of membranes?

A

From 18% to 75%

ESA 2- Membranes and Receptors (13 decks)

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