Containment: From Lipids To Membranes Flashcards
(107 cards)
1
Q
Why do we think cell membranes existed before the RNA world?
A
To prevent diffusion of components
2
Q
Amphipathic
A
Having both hydrophilic and hydrophobic parts
3
Q
What is the hydrophobic effect ?
A
In water, fatty acids spontaneously form micelles, membranes and vesicles, depending on pH
4
Q
How large is a micelle?
A
~20nm
5
Q
Where are fatty acids produced abiotically
A
In geysers, catalysed by minerals
6
Q
What naturally happens to vesicles with content?
A
- cause osmotic pressure
- tend to grow
- break up: abiotic ‘cell’ division
7
Q
What do current membranes mainly consist of?
A
- phospholipids
- hopanoids/steroids
- proteins
8
Q
Integral proteins aka
A
Intrinsic proteins
9
Q
Peripheral proteins aka
A
Extrinsic proteins
10
Q
What are the two main classifications of membrane lipids
A
- Phospholipids
- Hopanoids
11
Q
What is the main membrane steroid?
A
Cholesterol
12
Q
What are the two main classifications of phospholipids?
A
- phosphoglycérates
- sphingolipids
13
Q
What structure do phospholipids spontaneously organise themselves into, and why?
A
- lipid bilayers (membranes)
- they have ‘thicker’ hydrophobic tails
14
Q
What are the two halves of the phospholipid bilayer referred to as?
A
Leaflets
15
Q
What is the hydrophobic effect on phospholipids?
A
In water, phospholipids spontaneously form lipid bilayers
16
Q
Describe phosphoglycérides
A
- 3x components: phosphate, glycerol linker, 2x fatty acids
- polar hydrophilic head
- nonpolar hydrophobic tail
- ester bonds
17
Q
Give an example of a phosphoglyceride
A
Phospho-diglyceride
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
19
Q
What are factors that can vary in phospholipids?
A
- tail length (C14-C24)
- tail saturation (C=C v unsaturated)
- head group
20
Q
Give an example of a sphingolipid
A
Phospho-ceramide
21
Q
What do longer fatty acids tails do?
A
- Increase membrane thickness
- Decrease membrane fluidity
22
Q
Describe trans fatty acids
A
- No kink
- rare
23
Q
Describe cis fatty acids
A
kink
24
Q
What does unsaturated lipids do to membrane fluidity ?
A
Increase it
25
What are the most common head groups on phospholipids
1. Choline
2. Ethanolamine
3. Glucose
4. Glycerol
5. Inositol
6. Serine
26
Headgroups have roles in:
1. Protein-membrane interactions
2. Signalling
3. Recognition
27
In which classification of organisms are hopanoids found?
Prokaryotes
28
In which classification of organisms is cholesterol found?
Eukaryotes
29
Describe hopanoids
Pentacyclic compound
30
Describe cholesterol
- Tetracyclic compound
- steroid
31
What do hopanoids and cholesterol do?
- intercalate into bilayer
- increase membrane stiffness
32
Describe hopanoids and cholesterol
Flat, hydrophobic molecules
33
List the two types of lipid storage
1. Lipid droplet
2. Triglycerates (fats/oils)
34
List the 2 types of lipid movement:
1. Lateral diffusion
2. Transverse diffusion
35
Describe lateral diffusion of lipids in membranes
- fast
- 1 micrometer per second
36
Describe transverse diffusion of lipids in membrane
- flip-flop
- rare, depending on lipid
37
Flippases
Proteins that catalyses flip-flop of specific lipids, causing asymmetry of lipids between leaflets
38
List the 3 types of membrane protein
1) integral
2) peripheral
3) membrane-anchored
39
List the 3 types of integral membrane protein
1. α-helix
2. Helical bundle
3. β-bundle
40
Give an example of an α-helix structure
Receptors
41
Give examples of helical bundles
- transporters
- enzymes
- receptors
42
Give an example of a β-barrel
Transporters
43
Describe integral membrane proteins
Hydrophobic side chains decorate surface of transmembrane regions
44
TMD
transmembrane domain
45
Describe peripheral membrane proteins
Proteins that associated with membrane lipids and proteins via polar interactions
46
List the two types of membrane-anchored proteins
1. Cytoplasmic
2. Extracellular
47
Give the 3 main cytoplasmic protein lipidations
1. N-myristoylation
2. Prenylation
3. S-acylation
48
Describe S-acylation
- PTM
- reversible (not a very strong bond)
- on Cys
- cytoplasmic palmitoyl linked to sulfate on serine residue
49
Describe N-myristoylation (type of lipidation)
- 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
Describe prenylation
- PTM
- irreversible
- on Cys in C terminal CaaX motif
51
Give the prokaryotic extracellular protein lipidation
Lipoprotein
52
Describe lipoprotein lipidation
- PTM
- on N-terminal Cys
53
Describe the main extracellular eukaryotic protein lipidation
- GPI anchor
- cotranslational
- C-terminal Glycosyl-Phosphatidyl-Inositol
54
Describe the movement of membrane proteins:
- some move laterally
- no transverse diffusion
55
Describe membrane asymmetry
- lipid (and protein) distribution over leaflets is not equal
- PTMs are different outside/inside
- maintained by flippases
- conserved during vehicular transport
56
How are micro/nano domains created in liposomes?
Lipids with different properties
57
Nanodomain aka
Lipid raft
58
What is a nanodomain?
- local, robust, dynamic membrane region with physically different lipid and protein composition
59
Which gases can permeate membranes?
CO2, O2
60
Which hydrophobic molecules can penetrate membranes?
Benzene, steroids
61
Which small polar molecules can penetrate membranes?
Water, ethanol (some resistance)
62
What happens to large, polar molecules on membrane contact
- e.g. glucose, sucrose
- Some get through, most repelled
63
What happens to charged molecules on membrane contact
- all repelled
- e.g. amino acids, H+, Cl-, Na+, Ca2+
64
What is passive transport?
Transport in same direction as electrochemical gradient
65
How can passive transport be achieved?
- Through channels
- Through transporters (inducing conformational change)
- regulated
66
Describe passive transport
selective for specific molecules
67
How is passive transport regulated?
- ligand (gated)
- voltage gated
68
Define active transport
Transport against an electrochemical gradient
69
Where is the energy for active transport derived from?
- light
- metabolism
- electrochemical gradient of other coupled transported molecules (co-transport)
70
What are the two types of coupled transport?
1. Symporter
2. Antiporter
71
Symporter aka
Cotransporter
72
Antiporter aka
Exchanger
73
How does protein translocation occur?
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
SP
signal peptide
75
SRP
- signal recognition particle
- ribonucleoprotein complex
- contains translational pause domain, hinge and SP binding protein
- 4eu5 structure
- very ancient decision and machinery
76
What is the SRP membrane receptor in eukaryotes?
Plasmamembrane
77
What is the SRP receptor in eukaryotes
Rough ER
78
What is the role of the 2nd α-helix in SRP?
- stop signal to translocator
- causes dissociation from translocon
- transmembrane protein stops in the membrane
79
What is the role of the 3rd α-helix in SRP?
Start signal for translocator
80
Why is vesicles stage not stable?
It is determined by pH
81
How are phosphoglycerides created?
Acylation of phosphoglyercol
82
Describe sphingosine
- apolar long tail
- polar amine and hydroxyls head group
83
Why are sphingolipids a bit more stable?
Amide bonds
84
Rigidity synonym
Solidity
85
Head groups act as
Decorations
86
Describe the structure of hopanoids and cholesterol
- ring systems
- apolar
- flat surface
- very small hydroxyl polar group
87
Lateral diffusion is
Very dynamic
88
Describe flip flopping action
- one leaflet to the other leaflet
- bigger hydrophilic groups are harder to flip
89
Why flippase?
Creates chemical differences between leaflets
90
How can integral membrane proteins interact with hydrophobic lipids on the surface?
They are also hydrophobic on the surface
91
Describe peripheral proteins
- associated with membrane proteins or membrane directly
- contain hydrophilic structures
- have polar interactions
92
What is a helical bundle?
A hole in the membrane that selectively transports molecules
93
What is the residue number?
How far along the protein
94
How do we predict if a protein is hydrophobic?
- regions of hydrophobia through identification of helix number
95
How to extract peripheral proteins
- high salts and pH
- disturbs polar interactions
96
X =
Last residue on the protein
97
Where do lipidation reactions occur?
Cytoplasm
98
Are lipidations restricted to cell membranes?
No: can occur in mitochondrial and chloroplastic membranes too
99
GPI anchor function
Tethers extracellular proteins
100
Are kinases extracellular or intracellular
Intracellular
101
Describe liposomes
Lots of variation, highly dynamic
102
What happens under high concentrations of sphingolipids?
- more cholesterol accumulation
- more transmembrane helices
103
Can zwitterions penetrate cell membranes?
No, they are charged
104
What does passive mean?
No energy required
105
What can passive transport be thought of?
Selective diffusion
106
Protein translocation depends on
The sequence of the protein itself
107
Why are proteins stuck in the membrane?
Because of the transmembrane domain
