Exam Review - Chapter 19

Curvature and lateral tension hemifusion outer

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Unformatted text preview: f individual lipid molecules o What changes between states is the degree of motion (lateral and rotational) allowed to the lipid molecules Saturated fatty acids pack into the L0 gel phase Unsaturated fatty acids favor the Ld gel phase Sterols have paradoxical effects on bilayer fluidity o Interact with phospholipids containing unsaturated fatty acyl chains, compacting them and constraingin their motions in bilayers o Sterol association with sphingolipids and phospholipids with long, saturated fatty acyl chains tend to fluidize the bilayer Cells regulate their lipid composition to achieve a constant membrane fluidity under various growth conditions Transbilayer movement of lipids requires catalysis Transbilayer movement (flip- flopping) occurs very slowly at physiological temperatures o Has a positive free energy change o Requires a polar head group to move into the hydrophobic interior Lateral diffusion occurs very rapidly in the plane Flippases, floppases, and scramblases facilitate the transbilayer movement of lipids, providing a path that is energetically more favorable and faster than the uncatalyzed movement o Important for budding vesicles Flippases: catalyze translocation of the amino- phospholipids PE and PS from extracellular to the cytosolic leaflet of the plasma membrane o Contributes to the asymmetric distribution of phospholipids Phosphatidylserine (PS): its exposure to the extracellular leaflet triggers apoptosis and engulfment by macrophages o Consume 1 ATP per molecule of phospholopid translocated Floppases: move plasma membrane phospholipids from the cystolic to the extracellular lfealet o ATP dependent Scramblases: proteins that move any membrane phospholipid across the bilayer down its concentration gradient (higher concentration of phospholipids) o Activity is not ATP dependent Lateral diffusion of phospholipids occurs very rapidly o Can measure o FRAP: rate of fluorescence recovery after photobleaching, a measure of the rate of latral diffusion o fthe lipids o Another technique is following single particl o Follow movement of one lipid molecule Membrane proteins move the same way o Some associate to form large aggregates Microdomains: long, saturated acyl groups of sphingolipids can form more compact, more stable associations with the long rin...
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