physical properties Dynamic flexible structures Exist In various phases undergo phase transitions Not permeable 10 large polar solutes 110ns Permeable 10 small polar solutes nonpolar compounds Phases Depends on composition temp lipid bilayer can be lngel fluid a Liquid ordered state Lo Mr n E B E cid 15483 Mg BOM Ema EE EE E E 11 Heat produces thermal motion of side chains Lo Ld transition b Liquid disordered state Ld cid 15483 E E EEE cid 15483 cid 15483 cid 15483 r cid 15482 goq cid 15482 B cid 15483 EE cid 15483 cid 15483 cid 15483 cid 15483 s EBM cid 15483 a q O CB B B w cr T DK mf liquid ordered state Individual molecules do not move around liquid disordered state Individual molecules can move around Heating phase transition from get 10 fluid Under physiological conditions more fluid like must be fluid for proper function Fatty Acid Composition of E Coli Cells cultured at Different Temperatures Myristicaold Palmitic acid Palm 1 oleic acid Oleic acid Hydroxymyrlstlcacld percentage oftotalfattyacidsa 104 20 C 30 C 404 4 25 24 34 10 4 29 23 30 10 8 48 9 12 8 4 18 26 38 13 2 9 Organisms can adjust Membrane Composition Membrane fluidity Mainly fatty acid composition 1 melting point More fluid membranes require shorter more unsaturated fatty acids Melting temp Las double bonds are added Melting temp with length of saturated fatty acids Higher temp cells need more long saturated fatty acids Lower temp cells need more unsat Dynamics Lateral Diffusion Individual lipids undergo fast lateral diffusion within the leaflet Uncatalyzed Hi ii iHv cid 15483 11mm s a saturation Ratio 2 0 1 6 0 38 sterols Hopanols Increase Membrane Rigidity and Permeability E5 7Cholesterol T led fa ergosterol H 1 10 OH OH OH One particular hopanol Eukaryotes sterols Cholesterol in animals phytosterolsln plants ergosterol in fungi Prokaryotes hopanois tlhcatalyzedtransb layer flip flop diffusion GG MINIHAN HIM In days GGG GO GG 1411111111111111 Transverse Diffusion Spontaneous flips from one leaflet 10 another rare charged head group must transverse hydrophobic tall region of the membrane Flippases Special Enzymes catalyze transverse diffusion fhppase unique unidirectional bidirectional enzymes to catalyze lipid movement some use energy of ATP 10 move lipids against the concentration gradient Catalyzed transbilayer translocations Outside i q Eq i aqA h m h M f Inside ATP ADPTP ATP ADPTP Flippase IP type ATPase moves PE and PS from outer 10 cytosolic leaflet Floppase ABCtransporter moves phospholipids scramblase moves lipids in either direction from cytosolic 10 toward equilibrium Dynamics FRAP 7 Fluorescence recovery after photobleaching Monitor lateral lipid diffusion by monitoring rate of fluorescence return lipids can circumnavigate an E Coli cell in 1sec Rate off return of lipids the diffusion coefficient of a hpidintheleafietcanbe determined Rates of lateral diffusion are high up 101 Hm Sec I 1 8 8 i cid 15482 i i i g ffh BT f f f q in M m start Rafts Lipid distribution lnaslngle leaflet not random uniform contain clusters of glycosphlngohpldswth longer tnanusuaitans more ordered contain specific doubly triply acylated proteins allow segregation of proteins in the membrane Raft enriched in spningolipids cholesterol Outside Cholesterol r GP1 linked MMMMM M MN HMMMfpkM 1 1 1 0 EE EE i MoEFgHH H IM Palm Y MY 1091 prenylated protein Inside acylated protein protein outer leaflet I