Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24SteroidsSlide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Chapter 8 LipidsBiological Membranes Organized sheet-like assemblies consisting mainly of proteins & lipids Functions carried out by membranes are indispensable for life Plasma membrane give cells their individuality Eukaryotic cells contain internal membranes that form the boundaries for organellesPlasma MembraneBiological Membranes Not impervious walls Highly selective permeability barrier Control flow of information between cells & environment Proteins in the membrane carry out important functions Example: Mitochondrial inner membrane where ATP production takes placeCytoplasmWhat are membranes made of?Biological membranes are composed of proteins associated with a lipid bilayer matrixProteinLipid (bilayer)OligosaccharideCholesterolLipid composition of the plasma membrane & organelle of a rat hapatocyteNote the diversity of various membranesCommon Features of Biological Membranes Sheet-like structures with thickness of about 6 - 10 nm Consists of mainly lipids and proteins (Carbohydrates may be linked to proteins or lipids) Membranes lipids are relatively small molecules (Have both hydrophobic and hydrophilic groups) Membranes are asymmetric Membranes are fluid Specific proteins mediate distinctive functions of membranesWhat are Lipids? (Greek: lipos, fat)• Fourth major group of molecules found in cell• Lipids are not polymeric (unlike nucleic acids, proteins & polysaccharides)• Non water soluble (soluble in organic solvents such as methanol & chloroform)• Includes fats, oils, certain vitamins and hormonesMain functions of LipidsComponents of biological membranesLipids containing hydrocarbon chains serve as energy storesIntra and intercellular signalingLipid Classification Fatty acids Triacylglycerols Glycerophospholipids Sphingolipids Steroids Other lipids (Example: Eicosanoids)Fatty Acidso Carboxylic acids with long hydrocarbon side group (R-COOH)o Usually occur in esterified form (R-COOR)o Can be either saturated or unsaturated (contain double bonds)o Often are polyunsaturated (2 or more double bonds)o Double bonds have cis configuration and are non conjugated Stearic acidCH3(CH2)16COOHOleic acidCH3(CH2)7 CH=CH(CH2)7 COOHFully extended lowest energy conformationStearic acid118Stearic acid, alternative representation Oleic acid1918-Linolenic acid19181215Structural formulas of some C18 Fatty acids Pack Efficiently Stabilized by hydrophobic interactionsPresence of 1 or more Cis double bonds interfere with tight packingResults in less stable aggregates Packing of fatty acids into stable aggregatesMelting points of fatty acids Increase with increase in chain length (or molecular mass) For Example: Melting Point (oC)12:0 Lauric acid 44.218:0 Stearic acid 69.1 Decrease with the degree of unsaturation (or increase in double bonds) For Example: Melting Point (oC)18:0 Stearic acid 69.118:1 Oleic acid 13.218:2 Linoleic acid -9Triacyl Glycerols (triglycerides) Fatty acid triesters of glycerol Non polar, water insoluble Fats & oils are mixtures of triacyl glycerol Function as energy reservoirs in animals Not components of biological membranesFats are good way to store metabolic energy More energy than sugars or proteins which are partially oxidized Fats are non-polar and are stored in anhydrous form (unlike glycogen which binds twice its weight of water)Fatty acid composition of 3 food fatsOlive oil, butter, and beef fat are mixtures of triacylglycerols with different fatty acid compositionQuestion:Why is butter a solid while olive oil is liquid at 25oC?The principal class of storage and membrane lipidsGlycerophospholipids (or phosphoglycerides)Glycerol-3-phosphateGlycerophospholipids Major lipid components of biological membranes Derived from glycerol-3-phosphate whose C1 and C2 positions are esterified with fatty acids Phosphoryl group is linked to a group “X” Amphiphilic molecule: non-polar hydrocarbon tail polar phosphoryl X “heads”Symbol for phospholipid moleculePolar head groupHydrocarbon TailsLipid BilayerOutsideInsideQuestion: Can lipids form abilayer as shown here?Plasmalogen Glycerophospholipids At C1 position there is , -unsaturated ether linkageinstead of ester linkage Functions of most plasmalogen not well understoodEthanolamine, choline & serine form the most common plasmalogen head groupsCholineSphingolipids Major membrane components Derived from C18 amino alcohol, sphingosine Double bond of sphingosine has trans configurationSphingomyelins Most common sphingolipid With a phosphocholine or phosphoethanolamine head groups Although sphingomyelins differ chemically from PC and PE their conformation and charge distribution are similarSimilarities in shape and in molecular structure of PC & sphingomyelinThe specificities of phospholipasesPhospholipids & sphingolipids are degraded in lysosomeshydrolytic enzymesSteroids Structure consists of 3 6-membered rings & one 5-membered ring, all fused together Cholesterol is the most common steroid in animals (& precursor for all other steroids in animals) Steroid hormones serve many functions in animals - including salt balance, metabolic function and sexual functionCholesterolLipids as intracellular signalsEicosanoids carry messages to nearby cellsSteroids derived from cholesterolVitamin D3 productionLight capturing pigmentLipids as pigmentsBased on the isoprene structure All sterols (including cholesterol) are terpene-based molecules Steroid hormones are terpene-based Vitamins A, D, E, and K, are all compounds synthesized by the condensation of multiple isoprene units TerpenesVitamin A1, its precursor, and derivativesOther biologically active isoprenoid compoundsSeparation of analysis of lipidsRed blood cellsUnsealed RBC membranesLysing of the cells followed by washing Purified phospholipid mixtureExtraction of phospholipids using methanol chloroform mixture + an antioxidantChloroform layer Quantification of various phospholipids in red blood cellsDried &
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