PL1003 Topic 5 Lecture 5.1 Cell Membranes Lipids PDF

Cell membranes 1 The lipid bilayer Stuart Cruickshank  The cell (plasma) membrane Not all identical All share the same basic architecture Lipid bilayer Transmembrane proteins Proteins and glycolipids 5 December 2 2 024  The cell (plasma) membr...

Cell membranes 1 The lipid bilayer Stuart Cruickshank  The cell (plasma) membrane Not all identical All share the same basic architecture Lipid bilayer Transmembrane proteins Proteins and glycolipids 5 December 2 2 024  The cell (plasma) membrane A selective barrier: regulates the flow of material in and out of the cell Ion channels, transporters, receptors, enzymes and vesicular transport Communication (cell-cell and cell-environment) Tight junctions, adherens junctions and gap junctions 5 December 2 3 024  Phospholipids 5 December 2 4 024  The lipid bilayer Nature of fatty acids determines fluidity Glycolipid Fluidity influences electrical activity Phospholipids: Hydrophilic head Key features are shapes Lipid bilayer and melting temperatures Hydrophobic tail Explains much of why some fats are ‘good’ and others ‘bad’ 5 December 2 5 024  Stearic acid Animal fat (lard etc) Melting temperature 69oC (solid at room temp) a, b and w carbon atoms 5 December 2 6 024  Oleic acid 18C; 1 double bond; cis 16oC ‘trans’ shape Different properties Less fluid Many of these fats are ligands Affinities altered ‘Bad’ 5 December 2 7 024  Polyunsaturates Arachidonic acid; 20C; w-6 Other fats converted to AA Source of eicosanoids DHA 22C; 6 double bonds EPA 20C; 5 double bonds Both w-3 fats (fish oils) Low melting temperatures Stored in membrane (produce eicosanoids) 5 December 2 8 024  Fluidity Ion channels are transmembrane proteins Activity requires shape changes Influenced by fluidity of membrane Conduction possibly enhanced 5 December 2 9 024 5 December 2 10 024  Eicosanoids Bioactive lipids Prostaglandins, leukotrienes, thromboxanes and prostacyclin Cardinal signs of inflammation Control of BP, clotting, immune system modulation, reproductive processes, sleep/wake cycle 5 December 2 11 024  Cyclic and linear pathways 5 December 2 12 024  Important eicosanoids Prostacyclin and TXA2 Balance between these two reflects health of cardiovascular system TXA2: Potent vasoconstrictor; VSMC contraction; Activates platelets (tends to trigger thrombosis); Triggers expression of endothelial adhesion molecules; Promotes atherosclerosis (potential drug target) Prostacyclin: Anti-platelet; Relaxation of VSMC; Inhibits proliferation of VSMC; Enhances cardiac contractility; Anti-inflammatory TXA 5 December 2 3 (fish oil product) has none of the same effects as 13 024  Receptors 5 December 2 14 024