CellBio_Lecture3_Membranes.docx

Cholesterol prevents the fatty acid tails of

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The ring structure is non-polar rigid and the hydrocarbon tail is also non polar but it is also less rigid. Cholesterol prevents the fatty acid tails of neighboring lipid molecules from packing together tightly. and crystalizing. this makes the membrane less deformable and more rigid. provides mechanical support and membrane even less permeable to small water soluble proteins. Different cell membranes have different lipid compositions.
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Two leaflets of a given membrane can also often have different lipid compositions (and hence different properties of functional importance) For example: plasma membrane of human red blood cell PC, PS, PE, sphingomyelin an glycolipids PE and PS are not present on the side facing the extracellular space; whereas all glycolipids an most sphingomyelin and PC are found only on the side facing the extracellular space. The sugar molecules (e.g. sialic acid) on some glycolipids function as receptors for some viruses and for proteins on surface of other cells. Therefore there is an asymmetry in the bilayer Within certain membranes (e.g., pasta membrane) there are micro-domains (50 nm in diameter) especially enriched in sphingolipids and cholesterol. Because sphingolipids tend to have longer and straighter carbon chains these lipid rafts tend to be thicker. Specific membrane proteins (including those with longer trans-membrane domains) are also enriched in lipid rafts. Small head of cholesterol perfect to go next to sphingomyelin. Sphingomyelin is longer and straighter but also get’s glycosylated, these head groups can be very large. Components of Membranes: Lipids & Proteins Protiens: 2 types 1. integral membrane proteins 1. hydrophobic domain insterted into membrane 2. lipid anchored proteins: covalent link of protein to a lipid or fatty acid which inserts in to the membrane 2. peripheral membrane proteins. 2 types of membrane proteins: integral and peripheral integral can be transmembrane or lipid anchored A small number of integral membrane proteins are known to associate with specific lipid molecules that affect the activities of such proteins Lipid anchored examples would be frankly and GPI anchors like in slide image
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  • Spring '09
  • BUSHART
  • sphingomyelin

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