fluid mosaic model of membranes - vscht.czold-biomikro.vscht.cz/vyuka/psychro/prague_membrane... ·...
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Fluid mosaic model of membranes
Water-Ice Phase Transition
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Membrane lipid adaptation to cold
• Main changes in fatty acyl composition
• Smaller changes in head group
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Membrane lipid fatty acyl adaptation to cold
• more unsaturation
• more branching (anteiso and/or iso)
• shorter chain length
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Membrane lipid fatty acyl adaptation to cold
• more unsaturation
• more branching (anteiso and/or iso)
• shorter chain length
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Unsaturated fatty acids
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Cis and trans unsaturated fatty acids
Liquid-crystalline Lipid Phase
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Membrane lipid fatty acyl adaptation to cold
• more unsaturation
• more branching (anteiso and/or iso)
• shorter chain length
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CH2 CH2 CH2 CH3
straight-chain
CH2 CH2 CH CH3
CH3
iso-branched
CH2 CH CH2 CH3
CH3
anteiso-branched
Fluidising effect : Anteiso > Iso > Straight
Methyl-branched fatty acids
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Membrane lipid fatty acyl adaptation to cold
• more unsaturation
• more branching (anteiso and/or iso)
• shorter chain length
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Liquid-crystallineto gel phasetransition
Liquid-crystalline
Phase Gel Phase
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Liquid-crystallineto gel phasetransition
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Lipid fluidity influences membrane proton permeability
Homeo-proton Permeability Adaptation
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Decreasedtemperature
Liquid-crystallineto gel phasetransition
Bilayer (lamellar) to non-bilayer
(e.g. hexagonal) phasetransition
Homeoviscous adaptation Homeophasic adaptation
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Bilayer (lamellar) to non-bilayer
(e.g. hexagonal) phasetransition
Antarctica Dry Valleys (Taylor Valley)
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Bilayer (lamellar) phase
Phosphatidylglyerol
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Non-bilayer hexagonal phase
Unsaturated Phosphatidylethanolamine
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Decreasedtemperature
Altered lipid fatty acyl composition
Altered lipid head group composition
Homeophasic adaptation
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Decreasedtemperature
• Increase inunsaturation
• Increase in cis/trans ratio
• Changes in methyl branching
• Shortening of acylchain length
Rapid Slow
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Precursors
Intermediate
Saturated Monounsaturated FA FA
Anaerobic pathway Aerobic pathway
Precursors
FAS
SFA
Desaturase
UFA
Bacterial unsaturated fatty acid biosynthesis
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Acetyl-ACP
ß-Hydroxy-decanoyl-ACP
Trans-2-decenoyl-ACP Cis-3-decenoyl-ACP
16:0 16:1Δ9
18:0 18:1Δ11
Saturated Unsaturated
Anaerobic pathway
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Cellular organisation of unsaturatedfatty acid and membranephospholipid biosynthesis
Cell membrane – Lipid bilayer
UFA-PL SFA-PL
Precursors Anaerobic
pathway FAS
UFA SFA
Phospholipid biosynthesis
Desaturase
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Importance of hydrophobic α-helices in protein-lipid interactions
Integral Membrane Protein