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Biochemistry > Membranes > Flashcards

Membranes Flashcards

1
Q

4 kinds of membrane proteins?

A

Receptors
Ion channels
Adhesion molecules
Transporters

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2
Q

What do ion channels do?

A

Mediate electrical signalling between cells

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3
Q

4 types of receptors

A

Ligand-gated ion channels
G-protein-coupled receptors
Kinase-linked receptors
Nuclear receptors

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4
Q

What kind of receptor does glucagon activate?

A

G-protein coupled receptors

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5
Q

What kind of receptor does insulin activate?

A

Receptor tyrosine kinases

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6
Q

Example of intracellular receptor

A

Nuclear receptor

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7
Q

What receptors do many drugs utilise?

A

G-protein coupled receptors

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8
Q

What does the alpha subunit stimulate when the G-protein coupled receptor is stimulated?

A

AC- adenelaine cyclase

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9
Q

What secondary messenger does AC produce?

A

Cyclic AMP

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10
Q

Example of what activates G-protein coupled receptors?

A

Glucagon
Adrenalin

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11
Q

Example of what activates steroid hormone receptors

A

Sex hormones
Cortisol

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12
Q

Are the responses to steroid hormone receptors faster or slower than G-protein coupled receptors?

A

Slower, because they are activating gene expression which can take days
G-protein receptors act immediately, very quick

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13
Q

What has a role in metastasis of cancer?

A

Integrins

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14
Q

Some common functions of membranes (6)

A

Define boundaries of cell
Allow import and export
Retain metabolites and ions within the cell
Sense external signals and transmit information into the cell
Nerve signals
Store energy (proton gradient)

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15
Q

What is the main structure formed of?

A

Lipid bilayer

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16
Q

What stabilises membranes?

A

Noncovalent forces, especially hydrophobic effect and van der waals

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17
Q

What are membrane lipids?

A

Small amphipathic molecule that form closed biomolecular sheets

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18
Q

Are the inner and outer surfaces of membranes the same?

A

No they differ which gives asymmetry

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19
Q

What does the closed bimolecular sheet that membranes form prevent?

A

The movement of polar or charged molecules

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20
Q

What do membrane proteins mitigate?

A

The impermeability of membranes
Allow movement of molecules and information

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21
Q

Are membranes covalent or non covalent assemblies?

A

Noncovalent

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22
Q

3 major structures observed when lipids aggregate into structures in water

A

Michelle’s
Bilayers
Liposomes

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23
Q

What does the which structure is formed when lipids aggregate depend on?

A

Type of lipid
Concentration

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24
Q

What are micelles?

A

Spherical structure containing amphipathic molecules arranged with hydrophobic regions in the interior

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25
Q

When is the micelles lipid structure favoured?

A

When the cross sectional area of the head of the group is greater than that of the acyl side chains

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26
Q

When is the bilayer lipid structure favoured?

A

When the cross sectional area of the head of the group and the acyl side chains are similar

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27
Q

When does the liposome (vesicle) lipid structure form?

A

When the bilayer folds on itself to form a hollow sphere

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28
Q

Different name for liposomes

A

Lipid vesicles

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29
Q

Which part of lipids are hydrophobic?

A

Fatty acid tail

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30
Q

What kind of movement does the fluid mosaic model allow for?

A

Lateral movement

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31
Q

Does the fluid mosaic model allow for rotation through the membrane?

A

No

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32
Q

2 types of lipid movement in membranes

A

Lateral diffusion
Transverse diffusion (flip-flop)

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33
Q

Which lipid movement in membranes is rapid?

A

Lateral diffusion

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34
Q

Which lipid movement in membranes is very slow?

A

Transverse diffusion

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35
Q

What disrupts the tight packing of the fatty acid chains?

A

Cholesterol

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36
Q

5 physical properties of membranes

A

Dynamic and flexible structures
Can exist in various phases and undergo phase transitions
Not permeabe to large polar solutes and ions
Permeable to small polar solutes and non polar compounds
Permeability can be artificially increased by chemical treatment

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37
Q

2 liquid phases of the membrane

A

Liquid-ordered state (gel phase)
Liquid-disordered state (fluid phase)

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38
Q

Do individual molecules move around in the liquid-ordered state?

A

No

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39
Q

Do individual molecules move around in the liquid-disordered state?

A

Yes

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40
Q

What causes phase transition from gel to fluid?

A

Heating

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41
Q

What are membranes more like under physiological conditions, fluid-like or gel-like?

A

Fluid-like

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42
Q

What do more fluid membranes require?

A

Shorter and more unsaturated fatty acids

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43
Q

What happens to the melting point when double bonds are added to the fatty acids?

A

It decreases

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44
Q

How does the length of saturated fatty acids affect the melting temperature?

A

Increased length increases the melting point

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45
Q

Why are transverse diffusions rare?

A

Because the charged head group must transverse the hydrophobic tail region of the membrane

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46
Q

Which enzymes catalyse transverse diffusion?

A

Flippase
Floppies
Scramblase

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47
Q

What does the enzymes that catalyse transverse diffusion use to move the lipids against the concentration gradient?

A

ATP

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48
Q

What does the lipid composition of membranes vary by?

A

Organisms
Tissues
Organelles

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49
Q

What does the unique lipid composition of each membrane type reflect?

A

The functional specialisation

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50
Q

What does membrane fluidity depend on?

A

Temperature
Lipid composition

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51
Q

What does the melting temperature depend on?

A

Length of fatty acids
Degree of cis unsaturation

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52
Q

What does lipid rafts contain?

A

Clusters of glycosphingolipids with longer-than-usual tails
Specific doubly or triply acylated proteins

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53
Q

Are lipid rafts more or less ordered?

A

More

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54
Q

What does lipids rafts allow segregation of?

A

Proteins in the membrane

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55
Q

What clusters together in membrane rafts?

A

Sphingolipids and cholesterol

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56
Q

What do lipid rafts do?

A

Help to moderate membrane fluidity
Function in signal transduction

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57
Q

What does the eukaryotic plasma membrane consist of?

A

Phospholipidbilayer with proteins and cholesterol embedded

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58
Q

Where do tyr and trp cluster in membranes?

A

At the non polar/polar intereface

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59
Q

What doe beta strands form in the membrane?

A

A pore

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60
Q

What signals do receptor proteins receive?

A

Light
Hormones
Neurotransmitters
Phereomones

61
Q

What passes through channel, gate and pump proteins?

A

Nutrients
Ions
Neurotransmitters

62
Q

When can integral membrane proteins be removed from the membrane?

A

In the presence of strong detergents

63
Q

When are peripheral (non-GPI linked) membrane proteins dissociated from the membrane?

A

During changes in ionic strength (pH changes)

64
Q

When are ampitrophic and GPI-linked proteins linked to the membrane?

A

During specific regulatory events

65
Q

What do peripheral membrane proteins associate with?

A

The polar head groups of membranes

66
Q

How are peripheral membrane proteins associated with the membrane?

A

Through ionic interactions with the lipids
or
Aqueous domains of integral membrane proteins

67
Q

How are peripheral membrane proteins removed?

A

Disrupting ionic interactions with either high salt or change in pH

68
Q

How can amphitropic proteins be conditionally attached to the membrane?

A

By covalent interaction with lipids or carbohydrates attached to lipids

69
Q

What is farnesylation

A

A type of prenylation, a post-translational modification of proteins by which an isoprenyl group is added to a cysteine residue

70
Q

Where can proteins be targeted by farnesylation?

A

The inner leaflet of the plasma membrane

71
Q

What can farnesylation be an intermediate in?

A

The lipidation of proteins

72
Q

What catalyses the farnesylation reaction?

A

Farnesyl transferase

73
Q

3 general types of membrane lipids

A

Phospholipids
Glycoplipids
Sterols

74
Q

Which is the major class of membrane lipids?

A

Phospholipids

75
Q

4 components of phospholipids

A

2 fatty acid tails
A platform
A phosphate
An alcohol

76
Q

2 common phospholipid platforms

A

Glycerol
Sphingosine

77
Q

Which kind of phosphilipds are the primary constituents of cell membranes?

A

Glycerophospholipids

78
Q

What kind of linkage do the fatty acids form with the first and second hydro groups?

A

Ester linkage

79
Q

Is the phosphate group of glycerophospholipids charged or not at physiological pH?

A

Charged

80
Q

What are glycerophospholipids named as?

A

Derivatives of phosphatidic acid

81
Q

What kind of fatty acids are in glycerophospholipids?

A

Both saturated and unsaturated

82
Q

Which is the major component of most eukaryotic cell membranes?

A

Phosphatidylcholine

83
Q

What is the backbone of sphingolipids?

A

A long chain amino alcohol sphingosine

84
Q

What kind of linkage is the fatty acid in sphingolipids joined to sphingosine via?

A

Amide linkage

85
Q

What is a polar head group connected to sphingosine by in sphingolipids?

A

Glycosidic or phosphodiester linkage

86
Q

What is sphingomyelin?

A

A common membrane lipid in which the primary hydroxyl group of sphingosine is esterfied to phosphorylcholine

87
Q

Where are sphingomyelin abundant?

A

In myelin sheath that surrounds some nerve cells

88
Q

What is sphingomyelin st5ructually similar to?

A

Phosphatidycholine

89
Q

What do membrane sphingolipids serve as?

A

Sources of intracellular messengers

90
Q

What are ceramide and sphingomyelin potent regulators of?

A

Protein kinases

91
Q

What is ceramide involved in th regulation of?

A

Cell division
Differentiation
Migration
Programmed cell death

92
Q

Can membrane lipids include carbohydrate moieties?

A

Yes

93
Q

What are glycolipids derived from?

A

Sphingosine

94
Q

Which are the simplest glycolipids (only containing a single sugar) ?

A

Cerebrosides

95
Q

How many sugar molecules can gangliosides contain?

A

7

96
Q

What do gangliosides have as their pola head groups?

A

Oligosaccharides

97
Q

Where are gangliosides present?

A

In the grey matter of the human brain

98
Q

Example of a cell type with relatively low membrane protein content

A

Schwann cell

99
Q

Example of a demyelination disease, impairing myelin assembly or damaging existing myelin

A

Multiple sclerosis

100
Q

What, in part, determines the blood groups?

A

Type of sugars located on the head groups in glycosphingolipids

101
Q

What is the structure of sugar determined by?

A

An expression of specific glycosyltransferases

102
Q

What removes one of the 2 fatty acids in lipids?

A

Phospholipases of the A type

103
Q

Which removes the other of the 2 fatty acids in lipids?

A

Lysophospholipases

104
Q

Where are structural lipids degraded?

A

In the lysosome

105
Q

What are phospholipids degraded by?

A

Phospholipases A-D

106
Q

What are gangliosides degraded via?

A

A series of enzymatic cleavages

107
Q

What does a failure to correctly degrade gangliosides result in?

A

Build-up of lipids in lysosomes
Dysfunction called lysosomal storage disorder

108
Q

What is the lysosome known as?

A

The cell’s recycling center

109
Q

What does an accumulation of gangliosides contribute to?

A

Neurodegeneration

110
Q

What is cholesterol?

A

A lipid based on a steroid nucleus
A steroid

111
Q

What is cholesterol modified by?

A

On one end: attachement of fatty acid chain
On the other end: hydroxyl group

112
Q

What does the hydroxyl group of cholesterol interact with in membranes?

A

Phospholipid head groups

113
Q

What is a sterol made up of?

A

Steroid nucleus: 4 fused rings
Hydroxyl group (polar head) in the A-ring
Various non polar side chains

114
Q

How many fused rings do sterols have?

A

4

115
Q

Are sterols planar?

A

Relatively

116
Q

What do steroid hormones regulate?

A

Gene expression

117
Q

What are bile acids?

A

Polar derivatives of cholesterol

118
Q

What do bile acids emulsify?

A

Dietary fats on the intestine

119
Q
A
120
Q

How do mammals obtain cholesterol?

A

From food
Synthesise it de novo in the liver

121
Q

Via what is cholesterol bound to proteins transported to tissues?

A

Blood vessels

122
Q

What are steroids?

A

Oxidized derivatives of sterols

123
Q

How do sterol differ from cholesterol?

A

They lack the alkyl chain

124
Q

Are steroids more or less polar than cholesterol?

A

More

125
Q

Where ar3e steroid hormones synthesized?

A

Gonads
Adrenal glands

126
Q

What are ether lipids?

A

lipids where one of the two acyl chains are attached to glycerol in ether linkage instead of ester

127
Q

What are platelets-activating factor?

A

Aliphatic ether analog of phosphatidylcholine

128
Q

What do platelet-activating factor stimulate?

A

The aggregation of blood platelets

129
Q

2 types of passive transport across the membrane

A

Simple diffusion
Facilitated diffusion

130
Q

2 types of cell surface receptors

A

Ligan gated ion channels
G-protein coupled receptors

131
Q

4 types of ligand activated receptors

A

Ligand-gated channels
Ligand binding receptor-enzyme
G protein-coupled receptor
Intergrin

132
Q

What mediates signal transduction for cellular response to extracellular stimuli?

A

Receptors

133
Q

Which receptor is very commonly used by drugs?

A

G-protein coupled receptors

134
Q

Which nucleotides do G protein-coupled receptors bind?

A

Guanine nucleotides GDP and GTP

135
Q

What subunits do G protein-coupled receptors have?

A

Heterotrimeric Alpha, beta and gamma subunits

136
Q

What alters G protein-coupled receptors?

A

GPCR’s binding of ligand

137
Q

Which is the largest family of integral membran proteins?

A

G protein-coupled receptors

138
Q

What is GPCR short for?

A

G protein-coupled receptors

139
Q

What do steroid hormone receptor activate?

A

Long term responses

140
Q

2 main functions of integral receptors

A

Attachment of the cells to the ECM
Signal transduction from ECM to cells

141
Q

What subunits are integrins composed of?

A

Alpha
Beta

142
Q

What kind of dimers are integrins?

A

Heterodimers

143
Q

What does, in large part, defines the metabolic activities of a given cell type?

A

The expression of transporters

144
Q

What does the nature of the membrane transporters dictate?

A

The biochemical processes that occur inside the cell

145
Q

What are molecules if they are lipophilic?

A

Hydrophobic

146
Q

Do lipophilic molecules require the assistance of proteins to cross the membrane?

A

No, they cross via simple diffusion

147
Q

Which molecules require a channel (facilitated diffusion and passive transport) to move across the membrane?

A

Polar
Fully charged molecules

148
Q

What allows for rapid movement of ions across membranes down their concentration gradient?

A

Ion channels

Biochemistry (28 decks)

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