Session 2.3b - Workbook Notes - Lecture 1 Flashcards
Properties of Membrane Bilayers (139 cards)
1
Q
Aim of the Lecture:
To introduce the basic structure of biological membranes.
A
Phospholipid bilayer with proteins studded frequently throughout, 45% cholesterol, and saturated with water.
2
Q
Aim of the Lecture:
You should be familiar with the lipid bilayer model for membrane
structure.
A
Singer-Nicholson model: membranes are fluid.
3
Q
LO:
Describe the main functions of biological membranes
A
1) Selectivity
2) Control
3) Communication
4) Recognition
5) Signal generation
4
Q
LO:
Describe the composition of biological membranes
A
40% lipid
60% protein
1-10% carbohydrate (dry weight)
+ 20% total weight = water.
5
Q
LO:
Describe the properties of a fluid membrane
A
x
6
Q
LO:
Describe the contribution of cholesterol to membrane stability
A
x
7
Q
What are the general functions of biological membranes (cells and organelles)?
A
- Continuous highly selective permeability barrier.
- Allows control of the enclosed chemical environment
- Communication - control the flow of information between cells and their environment
- Recognition - signalling molecules, adhesion proteins, immune surveillance
- Signal generation in response to stimuli - electrical, chemical
8
Q
Where are biological membranes found?
A
Around cells and organelles
9
Q
Explain how a biological membranes’ function is selectivity.
A
Continuous highly selective permeability barrier.
10
Q
Explain how a biological membranes’ function is to maintain control of its environment.
A
Allows control of the enclosed chemical environment
11
Q
Explain how a biological membranes’ function is communication.
A
Communication - control the flow of information between cells and their environment
12
Q
Give 3 examples of things the biological membrane can recognise.
A
Recognition - signalling molecules, adhesion proteins, immune surveillance
13
Q
Explain how a biological membranes’ function is signalling.
A
Signal generation in response to stimuli - electrical, chemical
14
Q
Give 2 examples of stimuli a membrane can recognise in signal generation.
A
Electrical, chemical.
15
Q
Give an example of two types of membrane.
A
E.g.
Plasma membrane
Mitochondrial membrane
16
Q
Why is the plasma membrane different to the mitochondrial membrane, for example?
A
Different membranes have specialised functions.
17
Q
What is the function of the plasma membrane?
A
All of the above functions (selectivity, control, communication, recognition, signalling)
18
Q
What is the specialised function of the mitochondrial membrane?
A
Energy conservation by oxidative phosphorylation
19
Q
Which membrane is involved in energy conservation by oxidative phosphorylation?
A
Mitochondrial membrane
20
Q
Give examples of membranes with specialised functions
A
e.g. Plasma membrane - all of the above functions.
e.g. Mitochondrial membrane - energy conservation by oxidative
phosphorylation
21
Q
What is the membrane composition?
A
Varies with source, but generally membranes contain approx:
40% lipid
60% protein
1-10% carbohydrate (dry weight).
22
Q
What is the dry weight of a membrane?
A
Varies with source, but generally membranes contain approx:
40% lipid
60% protein
1-10% carbohydrate
23
Q
What is the TOTAL membrane composition?
A
Varies with source, but generally membranes contain approx:
40% lipid
60% protein
1-10% carbohydrate
BUT, the membrane bilayer is a hydrated structure so 20% of TOTAL membrane weight is water.
24
Q
Do different membrane compositions vary?
A
Yes, with source, but they are approximately the same.
25
What is the lipid concentration in membranes?
Varies with source, but generally
| 40% dry weight
32% total weight
26
What is the protein concentration in membranes?
Varies with source, but generally
| 60% dry weight
48% total weight
27
What is the carbohydrate concentration in membranes?
Varies with source, but generally
| 1-10% dry weight
0.8-8% total weight
28
What is the water concentration in membranes?
(Remember membranes are hydrated structures)
20% total weight
29
Membranes contain approximately:
40% lipid
60% protein
1-10% carbohydrate
Do they contain anything else?
Yes, this is the dry weight, but membranes are hydrated structures
Around 20% of the total weight is water.
30
Describe the membrane lipid properties.
Amphipatic molecules - i.e. they contain both hydrophilic and hydrophobic moieties.
31
Define "amphipathic".
Contains both hydrophilic and hydrophobic moieties.
32
What term is used to describe something that contains both hydrophilic and hydrophobic moieties?
Amphipathic
33
What is the membrane lipid distribution?
Varies depending on cell type.
34
Name 2 facts of phospholipids and give an example.
Predominant lipid in membrane
A 3 carbon glycerol with a phosphate, head group and 2 fatty acids.
e.g. phosphatidylcholine
35
What is the predominant lipid in membranes?
Phospholipid
36
Give an example of a phospholipid.
Phosphatidylcholine
37
What is phosphatidylcholine?
A phospholipid with a choline head group. Phospholipids are the predominant lipids found in membranes.
38
Fig. 2 (left)
Label the image.
Phospholipid
39
Fig. 2 (right)
Label the image.
Phosphatidylcholine
40
Draw a phospholipid.
See Fig. 2 (left)
```
G
Fatty acid - L
Y
C
E
Fatty acid - R
O
L - Phosphate - Head Group
```
41
Draw phosphatidylcholine
See Fig. 2 (right)
Fatty acid - C
Fatty acid - C
C - Phosphate (P) - Choline
42
Describe the head group in phospholipids.
A range of polar head groups are employed
43
What chemical property do the head groups of phospholipids all contain?
Polar
44
Name 4 types of head groups found in phospholipids.
Choline
Amines
Amino acids
Sugars
45
Describe the fatty acid chains found in phospholipids.
Enormous variety, C16 and C18 most prevalent
46
What is the most common carbon length in fatty acid chains of phospholipids?
C16 and C18
47
What is an unsaturated fatty acid?
1 or more double bonds in the side chain
48
Double bonds in the side chain of a fatty acid is known as what?
Unsaturated fatty acid side chains
49
In what conformation are the double bonds found in unsaturated fatty acids?
Cis
50
What is the immediate structural effect of cis double bonds in unsaturated fatty acids?
They introduce a kink in the chain
51
What does the kink from cis double bonds in unsaturated fatty acids do to the overall structure/properties?
Reduces phospholipid packing
52
What is the significance of the structural effect produced by unsaturated fatty acids?
Unsaturated fatty acids = 1 or more cis double bonds in the side chain
Double bond = kink in the chain
Kink = reduces phospholipid packing
53
Give two examples of sphingolipids.
Sphingomyelin
| Glycolipids
54
What is sphingomyelin?
A sphingolipid, of which it is the only one not based on glycerol.
55
What is the only phospholipid not based on glycerol?
Sphingomyelin (a sphingolipid)
56
What is the conformation of sphingomyelin in the membrane?
Resembles other phospholipids.
57
Name 3 facts about sphingomyelin.
- A sphingolipid
- Only phospholipid not based on glycerol
- In the membrane, its conformation resembles other phospholipids
58
Fig. 3 (left)
Label this image.
Sphingomyelin
59
Draw sphingomyelin.
| Would not need to draw
See Fig. 3 (left)
Carbon backbone - phosphate - choline head group
Fatty acids perpendicular.
60
How do you get a glycolipid from sphingomyelin?
If the phosphocholine moiety is replaced with a sugar
61
What do you get if the phosphocholine moiety of sphingomyelin is replaced with a sugar?
Glycolipid
62
How do you form a glycolipid?
If the phosphocholine moiety of sphingomyelin is replaced with a sugar
63
What are glycolipids?
- A type of sphingolipid
- Derived from sphingomyelin (phosphocholine replaced with a sugar)
- Sugar containing lipids
64
Define glycolipid.
Sugar containing lipids
65
What is a sugar containing lipid known as?
Glycolipid
66
What are the two types of glycolipids?
Cerebrosides
| Gangliosides
67
What are cerebrosides?
Glycolipids with head group sugar monomers
68
What are gangliosides?
Glycolipids with head group oligosaccharides (sugar multimers)
69
What do we call glycolipids with head group sugar monomers?
Cerebrosides
70
What do we call glycolipids with head group oligosaccharides (sugar multimers)?
Gangliosides
71
Name the sugar-containing lipids with a single sugar head group and multiple sugar head groups.
Glycolipids
sugar monomers = cerebrosides
sugar multimers (oligosaccharides) = gangliosides
72
What is the difference between cerebrosides and gangliosides?
Cerebrosides are glycolipids with sugar monomer head groups.
Gangliosides are glycolipids with sugar multimer head groups (oligosaccharides)
(self mnemonic to remember:
cerebroside = 1 like one cerebral
gangliosides = many like many ganglions)
73
Compare and contrast cerebrosides and gangliosides.
They are both glycolipids (sugar-containing lipids derived from sphingomyelin, and are phospholipids found in the membrane)
However, cerebrosides are glycolipids with sugar monomer head groups, and gangliosides are glycolipids with sugar multimer head groups (oligosaccharides)
74
What is an oligosaccharide?
A carbohydrate composed of a small number of sugar molecules (>1)
75
What is a monosaccharide?
Carbohydrate with one sugar molecule
76
How is cholesterol related to plasma membrane lipids?
It is a plasma membrane lipid
77
How much cholesterol is in the membrane?
45% of the total membrane lipid
78
What is the most abundant lipid in the membrane?
```
A. Phospholipid
B. Sphingomyelin
C. Glycolipid
D. Cerebroside
E. Cholesterol
```
Answer =
A. Phospholipid (most abundant)
B & C are other types of lipid in the membrane.
D is a type of glycolipid, along with ganglioside.
E (cholesterol) makes up 45% of the lipids.
79
What are the lipids involved in membrane bilayers?
- Phospholipids
- Sphingolipids
- -- sphingomyelin
- -- glycolipids
- ---- cerebroside
- ---- ganglioside
- Cholesterol
80
Fig. 3 (right)
Label and caption this image.
Phospholipids
- Phosphoglycerides (phosphate, and two fatty acids)
- -- PtdSer (amino acid)
- -- PtdEtn (amine)
- -- PtdCho (choline)
- -- PtdIns (sugar)
- Sphingomyelin
Glycolipids
- Glucosyl-Cerebroside (sugar head - 6 C)
Fatty acid tails e.g.
- Palmitate (saturated)
- Oleate (monounsaturated)
Similarity of membrane lipid structures.
81
Draw the hierarchy of membrane lipid structures, include as much detail as necessary.
See Fig. 3 (right)
Phospholipids
- Phosphoglycerides (phosphate, and two fatty acids)
- -- PtdSer (amino acid)
- -- PtdEtn (amine)
- -- PtdCho (choline)
- -- PtdIns (sugar)
- Sphingomyelin
Glycolipids
- Glucosyl-Cerebroside (sugar head - 6 C)
Fatty acid tails e.g.
- Palmitate (saturated)
- Oleate (monounsaturated)
Similarity of membrane lipid structures.
82
What two structures do amphipathic molecules form in water?
MICELLES and BILAYERS
83
What is the significance of putting an amphipathic molecule in water?
It will form one of two structures, either a MICELLE or a BILAYER.
84
What forms a micelle or a bilayer?
An amphipathic molecule in water.
85
What is the favoured structure for phospholipids and glycolipids in aqueous media?
Bilayers
86
Bilayers are the favoured structure for what?
Phospholipids and glycolipids in aqueous media
87
How does bilayer formation occur?
Spontaneously in water due to vdW forces and stabilised by non-covalent forces
88
What are the bonds involved in bilayer formation?
- van der Waals attractive forces between hydrophobic tails
- co-operative structure is stabilised by non-covalent forces; electrostatic and hydrogen bonding between hydrophilic moieties and interactions between hydrophilic groups and water.
89
What drives spontaneous bilayer formation to occur in water?
van der Waals attractive forces between hydrophobic tails
90
Where do the vdW interactions occur in bilayers?
Between hydrophobic tails
91
What interactions occur between the hydrophobic tails of the bilayer?
van der Waals
92
How is the co-operative structure of a bilayer stabilised?
By non-covalent forces
93
What role do non-covalent forces play in the membrane bilayer?
They stabilise the co-operative structure of the lipid bilayer
94
What are the non-covalent forces involved in the co-operative structure of the lipid bilayer?
Electrostatic interactions
| Hydrogen bonds
95
Where do the electrostatic interactions of the lipid bilayer occur?
Between hydrophilic moieties
96
Where do the hydrogen bonds of the lipid bilayer occur?
Between hydrophilic moieties, and between hydrophilic groups and water
97
What bonds occur between the hydrophilic moieties?
Electrostatic and hydrogen bonding
98
What bonds occur between the hydrophilic groups and water?
(Electrostatic and?) hydrogen bonding
99
What is the role of the van der Waals forces in the lipid bilayer?
Occurs between hydrophobic tails to drive spontaneous bilayer formation in water
100
What is the role of the electrostatic interactions in the lipid bilayer?
Occurs between hydrophilic moieties to stabilise the co-operative structure
101
What is the role of the hydrogen bond interactions in the lipid bilayer?
Occurs between hydrophilic moieties to stabilise the co-operative structure, and between the hydrophilic groups and water.
102
What is the permeability to ions for pure lipid bilayers?
Very low permeability
103
____ lipid bilayers have a very low permeability to ions
Pure
104
What is the permeability to (most) polar molecules for pure lipid bilayers?
Very low permeability
105
What is the pure lipid bilayer permeability?
Very low for ions and most polar molecules.
106
What is the dynamics in lipid bilayers?
Membranes are fluid structures
107
How many modes of mobility are there for lipid molecules in the lipid bilayer?
4 permitted modes
108
What are the 4 permitted modes of mobility in a lipid bilayer?
1. Intra-chain motion
2. Fast axial rotation.
3. Fast lateral diffusion
4. Flip-flop - movement of lipid molecules from one half of the bilayer to
the other on a one for one exchange basis.
109
What is intra-chain motion?
Kink formation in the fatty acyl chains
110
What is fast axial rotation?
Rotation of the lipid bilayer around its axis
111
What is fast lateral diffusion?
Lateral diffusion of the bilayers within the same plane of the bilayer
112
What is 'flip flop' movement of lipid molecules?
Movement of lipid molecules from one half of the bilayer to
| the other on a one for one exchange basis.
113
What do unsaturated double bonds do to the packing of phospholipids?
Unsaturated double bonds in the fatty acid side chains disrupt the
hexagonal packing of phospholipids
114
Unsaturated double _____ membrane fluidity.
Increase
115
Describe the effect of unsaturated double bonds on membrane fluidity.
Unsaturated double bonds in the fatty acid side chains disrupt the hexagonal packing of phospholipids and so increase membrane fluidity.
116
What plays a role in stabilising the plasma membrane?
Cholesterol
117
Cholesterol plays what important role in the plasma membrane?
Stabilising the PM.
118
What are the functions of membrane proteins in relation to other proteins?
Membrane proteins carry out the distinctive functions of proteins
119
Give 6 membrane functions.
- Enzymes
- Transporters
- Pumps
- Ions channels
- Receptors
- Energy transducers
120
What is the protein content in the membrane?
Protein content can vary from approximately 18% in myelin (nerve cell ‘insulator’) to 75% in the mitochondria
Normally membranes contain approximately 60% dry weight of protein
121
What is the protein content percentage in membranes?
Can be anywhere from 18% to 75%; but normally ~60% dry weight of protein.
122
How much % of protein is found in the myelin membrane?
~18%
123
How much % of protein is found in the mitochonrial membrane?
~75%
124
What is myelin?
The nerve cell 'insulator'
125
What is the nerve cell 'insulator' known as?
Myelin
126
Give an example of a membrane which has a low protein content.
Myelin (~18%)
Normal = 60% dry weight
127
Give an example of a membrane which has a relatively high protein content.
Mitochondria (75%)
Normal = 60% dry weight
128
What is the normal approximate dry weight of protein?
Normal = 60% dry weight
129
How many modes of mobility is available in proteins of bilayers and what are they?
3 modes permitted:
- conformational change
- rotational
- lateral
130
What are the restraints on mobility of proteins in bilayers?
NO FLIP-FLOP
- lipid mediated effects - proteins tend to separate out into the fluid phase or cholesterol poor regions.
- membrane protein associations
- association with extra-membranous proteins (peripheral
proteins) e.g. cytoskeleton.
131
Which mode of motion is available to membrane phospholipids but not membrane proteins?
Flip flop
132
Flip flop movement occurs in what?
Membrane phospholipids (rarely) but NOT membrane proteins.
133
What are the lipid-mediated effects in protein mobility restraints?
Proteins tend to separate out into the fluid phase or cholesterol poor regions.
134
What is the fluid phase of the membrane?
The cholesterol-poor region
135
Cholesterol-poor regions of the membrane are also known as what?
Fluid phase region
136
Where do you tend to find proteins in the membrane?
In the cholesterol-poor regions
(usually proteins that require stabilisation such as enzymes that need structure are found in stabilised cholesterol-rich environment).
137
What are the membrane protein associations?
E.g. aggregates, tethering, neighbouring cells
138
Which types of proteins can make association with extra-membranous proteins?
Peripheral proteins
139
Give an example of extra-membranous proteins peripheral proteins can associate with?
Cytoskeleton
