The Membrane Bilayer Flashcards Preview

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

Flashcards in The Membrane Bilayer Deck (84):
1

What are the general functions of biological membranes?

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

2

What do biological membranes capture?

An area of solute

3

Why are biological membranes needed for communication?

Needed to control flow of information between cells and their environment

4

Between where do biological membranes control communication?

Can be outside the cell, or outside of an organelle

5

What do biological membranes need for communication?

Mechanisms to communicate with outside environment

6

What do membranes recognise?

Signalling molecules
Adhesion proteins 
Immune cells

7

What do adhesion proteins allow?

Cells to recognise each other

8

What stimuli do membrane generate signals in response to?

Electrical 
Chemical

9

What do different regions of the plasma membrane have?

May have different functions

10

What functions can different regions of the plasma membrane have?

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

11

Why is absorption of body fluids important?

Provides nutrients for cell growth

12

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

Can allow to look for nutrients to bring into the cell

13

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

Release neurotransmitter
Have receptors to recognise neurotransmitters

14

What is needed for electrical signal conduction?

Proteins allow an action potential to be conducted along axon

15

What have a change in shape of membrane result in?

A change in properties of a different region

16

Why is the plasma membrane ever changing?

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

17

What do different membranes have?

Specialised function

18

Give an example of a membrane with a specialised function

The mitochondrial membrane- specialised for energy conservation by oxidative phosphorylation

19

What does membrane composition vary depends upon?

The source of the membrane

20

Generally, what is the membrane composition when dry?

40% lipid
60% protein 
1-10% carbohydrate

21

What % of the membranes total weight is water?

20%

22

Why is water needed in membranes?

To make hydrophilic interactions

23

Why are hydrophilic interactions in membranes important?

To keep the bilayer organised

24

What kind of molecules are membrane lipids?

Amphipathic

25

What is meant by amphipathic?

Contain both hydrophilic and hydrophobic moiety

26

What does the distribution of membrane lipids vary depending on?

Cell type- it is tissue specific

27

What is the distribution of membrane lipids related to?

Function

28

What are the predominant lipids in membranes?

Phospholipids

29

What are phospholipids made up of?

Glycerol backbone
Two fatty acid chains

30

Are the two fatty acid chains in phospholipids the same?

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

31

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

Beween C14 and C24
C16 and C18 most prevalent

32

What is the importance of the C16 and C18 prevalence?

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

33

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

A kink

34

Where is sphingomyelin found?

In membranes

35

Why is sphingomyelin unique?

It is the only phospholipid based on glycerol

36

What are glycolipids?

When the phosphate head group is replaced with a sugar

37

What is a cerebroside?

A glycolipid with a single sugar residue

38

What is a ganglioside?

A glycolipid with an oligosaccharide is attached

39

In what ways are all membrane lipids similar?

Have a long aliphatic chains and a small head group

40

What is the importance of all membrane lipids being similar?

Keeps membrane thickness about the same

41

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

When proteins are added to the membrane

42

What is a lipid micelle?

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

43

What is a lipid bilayer?

Double sheet

44

How are lipid bilayers form?

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

45

Do phospholipids more naturally form bilayers or micelles?

Bilayers

46

What are bilayers able to do?

Enclose a space

47

How can lipid bilayers be clinically useful?

In drug delivery

48

How can lipid bilayers be used in drug delivery?

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

What is the lipid bilayer the favoured structure for?

Glycolipids in aqueous media

50

When is bilayer formation spontaneous?

In water

51

What is bilayer formation in water driven by?

The van der Waals attractive forces between the hydrophobic tails

52

What is the bilayer structure stabilised by?

Non-covalent forces

53

What non-covalent forces stabilise the bilayer structure?

Electrostatic
Hydrogen bonding
Interactions between hydrophilic groups and water

54

What is the permeability of pure lipid bilayers?

Very low to ions and most polar molecules

55

What are the methods of phospholipid motion?

Flexion 
Fast axial rotation 
Fast lateral diffusion 
Flip-flop

56

What is flexion?

Intra-chain motion

57

What causes flexion?

Kink formation in fatty acyl chains

58

Where does fast lateral diffusion occur?

Within the plane of the bilayer

59

How common is flip-flop?

Rare

60

What is flip-flop?

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

61

Why is flip-flop rare?

Because its thermodynamically unfavourable

62

Why is flip-flop thermodynamically unfavourable?

Because have to take a hydrophilic group through a hydrophobic domain

63

What kind of bonds influence the bilayer structure?

Cis double bonds

64

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

Reduces phospholipid packing

65

What does the reduction in phospholipid packing lead to?

Disruption of hexagonal packing of phospholipids

66

What is the result of the disruption of phospholipid packing?

Membrane is more dynamic/flui

67

Why do we need polyunsaturated fats in the diet?

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

68

What is cholesterol?

A plasma membrane lipid

69

What % of total membrane lipid does cholesterol make up?

45%

70

What kind of head group does cholesterol have?

Polar, hydrophilic

71

What structure does cholesterol have?

Rigid, planar, steroid ring structure

72

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

Largely single

73

What is the result of cholesterols structure?

It is very rigid

74

What does cholesterol abolish?

The endothermic phase transition of phospholipid membrane

75

What causes the endothermic phase transition?

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

76

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

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

77

What brings cholesterol into the phospholipid bilayer?

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

78

Does does bringing in of cholesterol bring into the membrane?

The rigid structure, which grafts onto phospholipid

79

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

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

80

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

They are paradoxical

81

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

Reduced phospholipid chain motion leads to reduced fluidity 
Reduced phospholipid packing leads to increased fluidity

82

What is the result of the paradoxical effects of cholesterol?

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

83

What functions of membranes do proteins carry out?

Enzymes
Transporters
Pumps
Ion channels 
Receptors
Energy transducers

84

What is the protein content of membranes?

From 18% to 75%