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Michaelmas Term 1 > Containment: From Lipids To Membranes > Flashcards

Containment: From Lipids To Membranes Flashcards

1
Q

Why do we think cell membranes existed before the RNA world?

A

To prevent diffusion of components

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2
Q

Amphipathic

A

Having both hydrophilic and hydrophobic parts

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3
Q

What is the hydrophobic effect ?

A

In water, fatty acids spontaneously form micelles, membranes and vesicles, depending on pH

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4
Q

How large is a micelle?

A

~20nm

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5
Q

Where are fatty acids produced abiotically

A

In geysers, catalysed by minerals

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6
Q

What naturally happens to vesicles with content?

A
  • cause osmotic pressure
  • tend to grow
  • break up: abiotic ‘cell’ division
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7
Q

What do current membranes mainly consist of?

A
  • phospholipids
  • hopanoids/steroids
  • proteins
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8
Q

Integral proteins aka

A

Intrinsic proteins

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9
Q

Peripheral proteins aka

A

Extrinsic proteins

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10
Q

What are the two main classifications of membrane lipids

A
  1. Phospholipids
  2. Hopanoids
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11
Q

What is the main membrane steroid?

A

Cholesterol

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12
Q

What are the two main classifications of phospholipids?

A
  • phosphoglycérates
  • sphingolipids
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13
Q

What structure do phospholipids spontaneously organise themselves into, and why?

A
  • lipid bilayers (membranes)
  • they have ‘thicker’ hydrophobic tails
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14
Q

What are the two halves of the phospholipid bilayer referred to as?

A

Leaflets

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15
Q

What is the hydrophobic effect on phospholipids?

A

In water, phospholipids spontaneously form lipid bilayers

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16
Q

Describe phosphoglycérides

A
  • 3x components: phosphate, glycerol linker, 2x fatty acids
  • polar hydrophilic head
  • nonpolar hydrophobic tail
  • ester bonds
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17
Q

Give an example of a phosphoglyceride

A

Phospho-diglyceride

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18
Q

Describe sphingolipids

A
  • 3x components: phosphate, sphingosine linkers, 1x fatty acid
  • polar hydrophilic head
  • nonpolar hydrophobic tail
  • ester bond connects phosphate and sphingosine
  • amide bond connects sphingosine and fatty acid
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19
Q

What are factors that can vary in phospholipids?

A
  • tail length (C14-C24)
  • tail saturation (C=C v unsaturated)
  • head group
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20
Q

Give an example of a sphingolipid

A

Phospho-ceramide

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21
Q

What do longer fatty acids tails do?

A
  1. Increase membrane thickness
  2. Decrease membrane fluidity
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22
Q

Describe trans fatty acids

A
  • No kink
  • rare
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23
Q

Describe cis fatty acids

A

kink

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24
Q

What does unsaturated lipids do to membrane fluidity ?

A

Increase it

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25
Q

What are the most common head groups on phospholipids

A
  1. Choline
  2. Ethanolamine
  3. Glucose
  4. Glycerol
  5. Inositol
  6. Serine
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26
Q

Headgroups have roles in:

A
  1. Protein-membrane interactions
  2. Signalling
  3. Recognition
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27
Q

In which classification of organisms are hopanoids found?

A

Prokaryotes

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28
Q

In which classification of organisms is cholesterol found?

A

Eukaryotes

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29
Q

Describe hopanoids

A

Pentacyclic compound

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30
Q

Describe cholesterol

A
  • Tetracyclic compound
  • steroid
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31
Q

What do hopanoids and cholesterol do?

A
  • intercalate into bilayer
  • increase membrane stiffness
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32
Q

Describe hopanoids and cholesterol

A

Flat, hydrophobic molecules

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33
Q

List the two types of lipid storage

A
  1. Lipid droplet
  2. Triglycerates (fats/oils)
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34
Q

List the 2 types of lipid movement:

A
  1. Lateral diffusion
  2. Transverse diffusion
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35
Q

Describe lateral diffusion of lipids in membranes

A
  • fast
  • 1 micrometer per second
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36
Q

Describe transverse diffusion of lipids in membrane

A
  • flip-flop
  • rare, depending on lipid
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37
Q

Flippases

A

Proteins that catalyses flip-flop of specific lipids, causing asymmetry of lipids between leaflets

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38
Q

List the 3 types of membrane protein

A

1) integral
2) peripheral
3) membrane-anchored

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39
Q

List the 3 types of integral membrane protein

A
  1. α-helix
  2. Helical bundle
  3. β-bundle
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40
Q

Give an example of an α-helix structure

A

Receptors

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41
Q

Give examples of helical bundles

A
  • transporters
  • enzymes
  • receptors
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42
Q

Give an example of a β-barrel

A

Transporters

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43
Q

Describe integral membrane proteins

A

Hydrophobic side chains decorate surface of transmembrane regions

44
Q

TMD

A

transmembrane domain

45
Q

Describe peripheral membrane proteins

A

Proteins that associated with membrane lipids and proteins via polar interactions

46
Q

List the two types of membrane-anchored proteins

A
  1. Cytoplasmic
  2. Extracellular
47
Q

Give the 3 main cytoplasmic protein lipidations

A
  1. N-myristoylation
  2. Prenylation
  3. S-acylation
48
Q

Describe S-acylation

A
  • PTM
  • reversible (not a very strong bond)
  • on Cys
  • cytoplasmic palmitoyl linked to sulfate on serine residue
49
Q

Describe N-myristoylation (type of lipidation)

A
  • PTM/ cotranslational
  • irreversible, v strong
  • on N terminal Gly
  • amino group with v strong slide bond on myristoyl attached after N-terminal methionine removal
50
Q

Describe prenylation

A
  • PTM
  • irreversible
  • on Cys in C terminal CaaX motif
51
Q

Give the prokaryotic extracellular protein lipidation

A

Lipoprotein

52
Q

Describe lipoprotein lipidation

A
  • PTM
  • on N-terminal Cys
53
Q

Describe the main extracellular eukaryotic protein lipidation

A
  • GPI anchor
  • cotranslational
  • C-terminal Glycosyl-Phosphatidyl-Inositol
54
Q

Describe the movement of membrane proteins:

A
  • some move laterally
  • no transverse diffusion
55
Q

Describe membrane asymmetry

A
  • lipid (and protein) distribution over leaflets is not equal
  • PTMs are different outside/inside
  • maintained by flippases
  • conserved during vehicular transport
56
Q

How are micro/nano domains created in liposomes?

A

Lipids with different properties

57
Q

Nanodomain aka

A

Lipid raft

58
Q

What is a nanodomain?

A
  • local, robust, dynamic membrane region with physically different lipid and protein composition
59
Q

Which gases can permeate membranes?

A

CO2, O2

60
Q

Which hydrophobic molecules can penetrate membranes?

A

Benzene, steroids

61
Q

Which small polar molecules can penetrate membranes?

A

Water, ethanol (some resistance)

62
Q

What happens to large, polar molecules on membrane contact

A
  • e.g. glucose, sucrose
  • Some get through, most repelled
63
Q

What happens to charged molecules on membrane contact

A
  • all repelled
  • e.g. amino acids, H+, Cl-, Na+, Ca2+
64
Q

What is passive transport?

A

Transport in same direction as electrochemical gradient

65
Q

How can passive transport be achieved?

A
  • Through channels
  • Through transporters (inducing conformational change)
  • regulated
66
Q

Describe passive transport

A

selective for specific molecules

67
Q

How is passive transport regulated?

A
  • ligand (gated)
  • voltage gated
68
Q

Define active transport

A

Transport against an electrochemical gradient

69
Q

Where is the energy for active transport derived from?

A
  • light
  • metabolism
  • electrochemical gradient of other coupled transported molecules (co-transport)
70
Q

What are the two types of coupled transport?

A
  1. Symporter
  2. Antiporter
71
Q

Symporter aka

A

Cotransporter

72
Q

Antiporter aka

A

Exchanger

73
Q

How does protein translocation occur?

A
  1. Hydrophobic SP emerges fro ribosome
  2. SRP binds to SP; blocks translation
  3. SRP binds to SRP membrane receptor
  4. SP enters protein translocator
  5. SRP and receptor dissociate; translation continues
  6. Signal peptidase cleaves after SP
  7. Ribosome dissociâtes post- translation
74
Q

SP

A

signal peptide

75
Q

SRP

A
  • signal recognition particle
  • ribonucleoprotein complex
  • contains translational pause domain, hinge and SP binding protein
  • 4eu5 structure
  • very ancient decision and machinery
76
Q

What is the SRP membrane receptor in eukaryotes?

A

Plasmamembrane

77
Q

What is the SRP receptor in eukaryotes

A

Rough ER

78
Q

What is the role of the 2nd α-helix in SRP?

A
  • stop signal to translocator
  • causes dissociation from translocon
  • transmembrane protein stops in the membrane
79
Q

What is the role of the 3rd α-helix in SRP?

A

Start signal for translocator

80
Q

Why is vesicles stage not stable?

A

It is determined by pH

81
Q

How are phosphoglycerides created?

A

Acylation of phosphoglyercol

82
Q

Describe sphingosine

A
  • apolar long tail
  • polar amine and hydroxyls head group
83
Q

Why are sphingolipids a bit more stable?

A

Amide bonds

84
Q

Rigidity synonym

A

Solidity

85
Q

Head groups act as

A

Decorations

86
Q

Describe the structure of hopanoids and cholesterol

A
  • ring systems
  • apolar
  • flat surface
  • very small hydroxyl polar group
87
Q

Lateral diffusion is

A

Very dynamic

88
Q

Describe flip flopping action

A
  • one leaflet to the other leaflet
  • bigger hydrophilic groups are harder to flip
89
Q

Why flippase?

A

Creates chemical differences between leaflets

90
Q

How can integral membrane proteins interact with hydrophobic lipids on the surface?

A

They are also hydrophobic on the surface

91
Q

Describe peripheral proteins

A
  • associated with membrane proteins or membrane directly
  • contain hydrophilic structures
  • have polar interactions
92
Q

What is a helical bundle?

A

A hole in the membrane that selectively transports molecules

93
Q

What is the residue number?

A

How far along the protein

94
Q

How do we predict if a protein is hydrophobic?

A
  • regions of hydrophobia through identification of helix number
95
Q

How to extract peripheral proteins

A
  • high salts and pH
  • disturbs polar interactions
96
Q

X =

A

Last residue on the protein

97
Q

Where do lipidation reactions occur?

A

Cytoplasm

98
Q

Are lipidations restricted to cell membranes?

A

No: can occur in mitochondrial and chloroplastic membranes too

99
Q

GPI anchor function

A

Tethers extracellular proteins

100
Q

Are kinases extracellular or intracellular

A

Intracellular

101
Q

Describe liposomes

A

Lots of variation, highly dynamic

102
Q

What happens under high concentrations of sphingolipids?

A
  • more cholesterol accumulation
  • more transmembrane helices
103
Q

Can zwitterions penetrate cell membranes?

A

No, they are charged

104
Q

What does passive mean?

A

No energy required

105
Q

What can passive transport be thought of?

A

Selective diffusion

106
Q

Protein translocation depends on

A

The sequence of the protein itself

107
Q

Why are proteins stuck in the membrane?

A

Because of the transmembrane domain

Michaelmas Term 1 (42 decks)

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