Lecture 4 - Lipids and Membranes

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Katie Flaherty
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Katie Flaherty
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Lipids def. and examples? Lipids: molecules in cells that are water-insoluble (hydrophobic) but soluble in organic solvents e.g. - Triacylglycerol’s (fats and oils) - glycerophospholipids and other membrane lipids - steroids and cholesterol
Triacylglycerol’s? Triacylglycerol’s are neutral fats involved in dietary and storage processes: •Hydrophobic molecules – cluster together in the cell (storage) •Form droplets in water or aqueous environment •Important energy storage molecules • 1 glycerol and 3 fatty acid chains
Glycerophospholipid structure? 1 glycerol, 2 fatty acid chains, phosphate group and amino alcohol attached to P-group
Nomenclature of Glycerophospholipids?
Glycerophospholipid, four common types and their structures?
Sphingomyelin structure? - Based on Sphingosine (rather than glycerol) which is quite like glycerol but has a permanent hydrocarbon chain -a fatty acid, phosphate and a polar head group (choline) is added to sphingosine to make sphingomyelin
Where is sphingomyelin found? it is found in myelin sheaths of neurons - its an important membrane phospholipid
2 types of membrane lipids? 1. Phospholipids - Glycerol based – glycerophospholipids - Sphingosine based – sphingomyelin 2. Glycolipids/glycosphingolipids - Sphingosine based – no phosphate, carbohydrate polar head group
Structure and function of a cerebroside? -based on sphingosine, no phosphate with a single sugar head (glucose or galactose) - important in brain cell membranes
Structure and function of Gangliosides? -sphingosine based, no phosphate with oligosaccharide head group -ABO blood group determinants
What can the structures of the fatty components of membranes be and what difference does it make to MP? 1. Saturated – only single c-c bonds 2. Mono saturated – one double c=c bond (if naturally occurring the fatty acid is nearly always in cis configuration) the double bond largely lowers MP 3. Polyunsaturated – two or more c=c bonds, melting point even lower
Effect of kinks in the hydrocarbon tail chain from double c=c bonds? cause looser packing of fatty acid tails, reducing van der waals interactions and increasing fluidity
How do bacteria respond to change in external temp? they vary the proportion of unsaturated fatty acids in the membrane in response to external temp
Effect of cholesterol on a membrane? - the rigid structure inserts between phospholipids – this modulates membrane fluidity - at high temperatures, it ‘stiffens’ the membrane by filling the space between unsaturated FA’s - at low temperatures it increases fluidity by preventing FA tails from packing too closely
Phosphatidylinositol function in cell membrane? for intracellular signalling and anchoring of carbohydrates and proteins
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