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ESA 1 - Introduction to Cell Physiology and Pharmacology > Session 2.3b - Workbook Notes - Lecture 1 > Flashcards

Session 2.3b - Workbook Notes - Lecture 1 Flashcards

Properties of Membrane Bilayers

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.

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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.

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3
Q

LO:

Describe the main functions of biological membranes

A

1) Selectivity
2) Control
3) Communication
4) Recognition
5) Signal generation

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4
Q

LO:

Describe the composition of biological membranes

A

40% lipid
60% protein
1-10% carbohydrate (dry weight)

+ 20% total weight = water.

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5
Q

LO:

Describe the properties of a fluid membrane

A

x

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6
Q

LO:

Describe the contribution of cholesterol to membrane stability

A

x

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7
Q

What are the general functions of biological membranes (cells and organelles)?

A
  1. Continuous highly selective permeability barrier.
  2. Allows control of the enclosed chemical environment
  3. Communication - control the flow of information between cells and their environment
  4. Recognition - signalling molecules, adhesion proteins, immune surveillance
  5. Signal generation in response to stimuli - electrical, chemical
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8
Q

Where are biological membranes found?

A

Around cells and organelles

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9
Q

Explain how a biological membranes’ function is selectivity.

A

Continuous highly selective permeability barrier.

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10
Q

Explain how a biological membranes’ function is to maintain control of its environment.

A

Allows control of the enclosed chemical environment

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11
Q

Explain how a biological membranes’ function is communication.

A

Communication - control the flow of information between cells and their environment

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12
Q

Give 3 examples of things the biological membrane can recognise.

A

Recognition - signalling molecules, adhesion proteins, immune surveillance

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13
Q

Explain how a biological membranes’ function is signalling.

A

Signal generation in response to stimuli - electrical, chemical

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14
Q

Give 2 examples of stimuli a membrane can recognise in signal generation.

A

Electrical, chemical.

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15
Q

Give an example of two types of membrane.

A

E.g.

Plasma membrane
Mitochondrial membrane

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16
Q

Why is the plasma membrane different to the mitochondrial membrane, for example?

A

Different membranes have specialised functions.

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17
Q

What is the function of the plasma membrane?

A

All of the above functions (selectivity, control, communication, recognition, signalling)

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18
Q

What is the specialised function of the mitochondrial membrane?

A

Energy conservation by oxidative phosphorylation

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19
Q

Which membrane is involved in energy conservation by oxidative phosphorylation?

A

Mitochondrial membrane

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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

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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).

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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

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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.

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24
Q

Do different membrane compositions vary?

A

Yes, with source, but they are approximately the same.

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25
Q

What is the lipid concentration in membranes?

A

Varies with source, but generally

40% dry weight
32% total weight

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26
Q

What is the protein concentration in membranes?

A

Varies with source, but generally

60% dry weight
48% total weight

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27
Q

What is the carbohydrate concentration in membranes?

A

Varies with source, but generally

1-10% dry weight
0.8-8% total weight

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28
Q

What is the water concentration in membranes?

A

(Remember membranes are hydrated structures)

20% total weight

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29
Q

Membranes contain approximately:

40% lipid
60% protein
1-10% carbohydrate

Do they contain anything else?

A

Yes, this is the dry weight, but membranes are hydrated structures

Around 20% of the total weight is water.

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30
Q

Describe the membrane lipid properties.

A

Amphipatic molecules - i.e. they contain both hydrophilic and hydrophobic moieties.

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31
Q

Define “amphipathic”.

A

Contains both hydrophilic and hydrophobic moieties.

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32
Q

What term is used to describe something that contains both hydrophilic and hydrophobic moieties?

A

Amphipathic

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33
Q

What is the membrane lipid distribution?

A

Varies depending on cell type.

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34
Q

Name 2 facts of phospholipids and give an example.

A

Predominant lipid in membrane

A 3 carbon glycerol with a phosphate, head group and 2 fatty acids.

e.g. phosphatidylcholine

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35
Q

What is the predominant lipid in membranes?

A

Phospholipid

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36
Q

Give an example of a phospholipid.

A

Phosphatidylcholine

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37
Q

What is phosphatidylcholine?

A

A phospholipid with a choline head group. Phospholipids are the predominant lipids found in membranes.

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38
Q

Fig. 2 (left)

Label the image.

A

Phospholipid

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39
Q

Fig. 2 (right)

Label the image.

A

Phosphatidylcholine

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40
Q

Draw a phospholipid.

A

See Fig. 2 (left)

G
Fatty acid - L
Y
C
E
Fatty acid - R
O
L - Phosphate - Head Group
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41
Q

Draw phosphatidylcholine

A

See Fig. 2 (right)

Fatty acid - C
Fatty acid - C
C - Phosphate (P) - Choline

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42
Q

Describe the head group in phospholipids.

A

A range of polar head groups are employed

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43
Q

What chemical property do the head groups of phospholipids all contain?

A

Polar

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44
Q

Name 4 types of head groups found in phospholipids.

A

Choline
Amines
Amino acids
Sugars

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45
Q

Describe the fatty acid chains found in phospholipids.

A

Enormous variety, C16 and C18 most prevalent

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46
Q

What is the most common carbon length in fatty acid chains of phospholipids?

A

C16 and C18

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47
Q

What is an unsaturated fatty acid?

A

1 or more double bonds in the side chain

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48
Q

Double bonds in the side chain of a fatty acid is known as what?

A

Unsaturated fatty acid side chains

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49
Q

In what conformation are the double bonds found in unsaturated fatty acids?

A

Cis

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50
Q

What is the immediate structural effect of cis double bonds in unsaturated fatty acids?

A

They introduce a kink in the chain

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51
Q

What does the kink from cis double bonds in unsaturated fatty acids do to the overall structure/properties?

A

Reduces phospholipid packing

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52
Q

What is the significance of the structural effect produced by unsaturated fatty acids?

A

Unsaturated fatty acids = 1 or more cis double bonds in the side chain

Double bond = kink in the chain

Kink = reduces phospholipid packing

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53
Q

Give two examples of sphingolipids.

A

Sphingomyelin

Glycolipids

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54
Q

What is sphingomyelin?

A

A sphingolipid, of which it is the only one not based on glycerol.

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55
Q

What is the only phospholipid not based on glycerol?

A

Sphingomyelin (a sphingolipid)

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56
Q

What is the conformation of sphingomyelin in the membrane?

A

Resembles other phospholipids.

57
Q

Name 3 facts about sphingomyelin.

A
  • A sphingolipid
  • Only phospholipid not based on glycerol
  • In the membrane, its conformation resembles other phospholipids
58
Q

Fig. 3 (left)

Label this image.

A

Sphingomyelin

59
Q

Draw sphingomyelin.

Would not need to draw

A

See Fig. 3 (left)

Carbon backbone - phosphate - choline head group

Fatty acids perpendicular.

60
Q

How do you get a glycolipid from sphingomyelin?

A

If the phosphocholine moiety is replaced with a sugar

61
Q

What do you get if the phosphocholine moiety of sphingomyelin is replaced with a sugar?

A

Glycolipid

62
Q

How do you form a glycolipid?

A

If the phosphocholine moiety of sphingomyelin is replaced with a sugar

63
Q

What are glycolipids?

A
  • A type of sphingolipid
  • Derived from sphingomyelin (phosphocholine replaced with a sugar)
  • Sugar containing lipids
64
Q

Define glycolipid.

A

Sugar containing lipids

65
Q

What is a sugar containing lipid known as?

A

Glycolipid

66
Q

What are the two types of glycolipids?

A

Cerebrosides

Gangliosides

67
Q

What are cerebrosides?

A

Glycolipids with head group sugar monomers

68
Q

What are gangliosides?

A

Glycolipids with head group oligosaccharides (sugar multimers)

69
Q

What do we call glycolipids with head group sugar monomers?

A

Cerebrosides

70
Q

What do we call glycolipids with head group oligosaccharides (sugar multimers)?

A

Gangliosides

71
Q

Name the sugar-containing lipids with a single sugar head group and multiple sugar head groups.

A

Glycolipids

sugar monomers = cerebrosides

sugar multimers (oligosaccharides) = gangliosides

72
Q

What is the difference between cerebrosides and gangliosides?

A

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
Q

Compare and contrast cerebrosides and gangliosides.

A

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
Q

What is an oligosaccharide?

A

A carbohydrate composed of a small number of sugar molecules (>1)

75
Q

What is a monosaccharide?

A

Carbohydrate with one sugar molecule

76
Q

How is cholesterol related to plasma membrane lipids?

A

It is a plasma membrane lipid

77
Q

How much cholesterol is in the membrane?

A

45% of the total membrane lipid

78
Q

What is the most abundant lipid in the membrane?

A. Phospholipid
B. Sphingomyelin
C. Glycolipid
D. Cerebroside
E. Cholesterol
A

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
Q

What are the lipids involved in membrane bilayers?

A
  • Phospholipids
  • Sphingolipids
  • – sphingomyelin
  • – glycolipids
  • —- cerebroside
  • —- ganglioside
  • Cholesterol
80
Q

Fig. 3 (right)

Label and caption this image.

A

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
Q

Draw the hierarchy of membrane lipid structures, include as much detail as necessary.

A

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
Q

What two structures do amphipathic molecules form in water?

A

MICELLES and BILAYERS

83
Q

What is the significance of putting an amphipathic molecule in water?

A

It will form one of two structures, either a MICELLE or a BILAYER.

84
Q

What forms a micelle or a bilayer?

A

An amphipathic molecule in water.

85
Q

What is the favoured structure for phospholipids and glycolipids in aqueous media?

86
Q

Bilayers are the favoured structure for what?

A

Phospholipids and glycolipids in aqueous media

87
Q

How does bilayer formation occur?

A

Spontaneously in water due to vdW forces and stabilised by non-covalent forces

88
Q

What are the bonds involved in bilayer formation?

A
  • 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
Q

What drives spontaneous bilayer formation to occur in water?

A

van der Waals attractive forces between hydrophobic tails

90
Q

Where do the vdW interactions occur in bilayers?

A

Between hydrophobic tails

91
Q

What interactions occur between the hydrophobic tails of the bilayer?

A

van der Waals

92
Q

How is the co-operative structure of a bilayer stabilised?

A

By non-covalent forces

93
Q

What role do non-covalent forces play in the membrane bilayer?

A

They stabilise the co-operative structure of the lipid bilayer

94
Q

What are the non-covalent forces involved in the co-operative structure of the lipid bilayer?

A

Electrostatic interactions

Hydrogen bonds

95
Q

Where do the electrostatic interactions of the lipid bilayer occur?

A

Between hydrophilic moieties

96
Q

Where do the hydrogen bonds of the lipid bilayer occur?

A

Between hydrophilic moieties, and between hydrophilic groups and water

97
Q

What bonds occur between the hydrophilic moieties?

A

Electrostatic and hydrogen bonding

98
Q

What bonds occur between the hydrophilic groups and water?

A

(Electrostatic and?) hydrogen bonding

99
Q

What is the role of the van der Waals forces in the lipid bilayer?

A

Occurs between hydrophobic tails to drive spontaneous bilayer formation in water

100
Q

What is the role of the electrostatic interactions in the lipid bilayer?

A

Occurs between hydrophilic moieties to stabilise the co-operative structure

101
Q

What is the role of the hydrogen bond interactions in the lipid bilayer?

A

Occurs between hydrophilic moieties to stabilise the co-operative structure, and between the hydrophilic groups and water.

102
Q

What is the permeability to ions for pure lipid bilayers?

A

Very low permeability

103
Q

____ lipid bilayers have a very low permeability to ions

104
Q

What is the permeability to (most) polar molecules for pure lipid bilayers?

A

Very low permeability

105
Q

What is the pure lipid bilayer permeability?

A

Very low for ions and most polar molecules.

106
Q

What is the dynamics in lipid bilayers?

A

Membranes are fluid structures

107
Q

How many modes of mobility are there for lipid molecules in the lipid bilayer?

A

4 permitted modes

108
Q

What are the 4 permitted modes of mobility in a lipid bilayer?

A
  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
Q

What is intra-chain motion?

A

Kink formation in the fatty acyl chains

110
Q

What is fast axial rotation?

A

Rotation of the lipid bilayer around its axis

111
Q

What is fast lateral diffusion?

A

Lateral diffusion of the bilayers within the same plane of the bilayer

112
Q

What is ‘flip flop’ movement of lipid molecules?

A

Movement of lipid molecules from one half of the bilayer to

the other on a one for one exchange basis.

113
Q

What do unsaturated double bonds do to the packing of phospholipids?

A

Unsaturated double bonds in the fatty acid side chains disrupt the
hexagonal packing of phospholipids

114
Q

Unsaturated double _____ membrane fluidity.

115
Q

Describe the effect of unsaturated double bonds on membrane fluidity.

A

Unsaturated double bonds in the fatty acid side chains disrupt the hexagonal packing of phospholipids and so increase membrane fluidity.

116
Q

What plays a role in stabilising the plasma membrane?

A

Cholesterol

117
Q

Cholesterol plays what important role in the plasma membrane?

A

Stabilising the PM.

118
Q

What are the functions of membrane proteins in relation to other proteins?

A

Membrane proteins carry out the distinctive functions of proteins

119
Q

Give 6 membrane functions.

A
  • Enzymes
  • Transporters
  • Pumps
  • Ions channels
  • Receptors
  • Energy transducers
120
Q

What is the protein content in the membrane?

A

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
Q

What is the protein content percentage in membranes?

A

Can be anywhere from 18% to 75%; but normally ~60% dry weight of protein.

122
Q

How much % of protein is found in the myelin membrane?

123
Q

How much % of protein is found in the mitochonrial membrane?

124
Q

What is myelin?

A

The nerve cell ‘insulator’

125
Q

What is the nerve cell ‘insulator’ known as?

126
Q

Give an example of a membrane which has a low protein content.

A

Myelin (~18%)

Normal = 60% dry weight

127
Q

Give an example of a membrane which has a relatively high protein content.

A

Mitochondria (75%)

Normal = 60% dry weight

128
Q

What is the normal approximate dry weight of protein?

A

Normal = 60% dry weight

129
Q

How many modes of mobility is available in proteins of bilayers and what are they?

A

3 modes permitted:

  • conformational change
  • rotational
  • lateral
130
Q

What are the restraints on mobility of proteins in bilayers?

A

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
Q

Which mode of motion is available to membrane phospholipids but not membrane proteins?

132
Q

Flip flop movement occurs in what?

A

Membrane phospholipids (rarely) but NOT membrane proteins.

133
Q

What are the lipid-mediated effects in protein mobility restraints?

A

Proteins tend to separate out into the fluid phase or cholesterol poor regions.

134
Q

What is the fluid phase of the membrane?

A

The cholesterol-poor region

135
Q

Cholesterol-poor regions of the membrane are also known as what?

A

Fluid phase region

136
Q

Where do you tend to find proteins in the membrane?

A

In the cholesterol-poor regions

(usually proteins that require stabilisation such as enzymes that need structure are found in stabilised cholesterol-rich environment).

137
Q

What are the membrane protein associations?

A

E.g. aggregates, tethering, neighbouring cells

138
Q

Which types of proteins can make association with extra-membranous proteins?

A

Peripheral proteins

139
Q

Give an example of extra-membranous proteins peripheral proteins can associate with?

A

Cytoskeleton

ESA 1 - Introduction to Cell Physiology and Pharmacology (10 decks)

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