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

The Membrane Bilayer Flashcards

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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
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%

ESA 2- Membranes and Receptors (13 decks)

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