LIPID STRUCTURES PROPERTIES and FUNCTIONS Lehninger Readings Chapter 10 pages 357 370 and Chapter 21 pages 845 847 874 At the end of this section you should be able to use lipid nomenclature to discuss lipid structure and function identify the function of a lipid based on its structure predict how changes in lipid structure will alter its function in biological systems and design an experiment to analyze a mixture of lipids You should be able to 1 Define lipids and compare lipids to other types of biomolecules 2 Describe the structural features found in common biological fatty acids and relate these to the properties and general functions of fatty acids 3 Correctly use fatty acid nomenclature draw the structures of palmitate stearate oleate linoleate ALA arachidonate EPA and DHA and interconvert between the structure the carbon skeleton shorthand and the systematic name for common fatty acids 4 Predict the physical and chemical properties of a fatty acid when given its structure 5 Identify the components found in lipids and classify lipids according to their basic structures and functions 6 Compare and contrast the structural physical and chemical properties of the various lipids and relate these to their biological functions 7 Predict the functions of lipids based on their physical and chemical properties 8 Recognize the structures of common membrane lipid head groups and relate these structures to the properties and functions of the head groups 9 Recognize examples of lipids produced from isoprene and describe some important cellular functions of these lipids 10 Identify the bonds in lipids that are cleaved by various lipases and describe the biological importance of lipases 11 Discuss examples of signaling carried out by lipids the sources of these signal molecules and the role of NSAIDs in disrupting signaling 12 Design an experiment to separate a mixture of lipids and identify the components of the lipids Page 1 Lipid Structures Properties and Functions 1 Define lipids and compare lipids to other types of biomolecules Lipids Definition The cellular components that are soluble in organic solvents chloroform methanol but sparingly soluble or insoluble in water General Properties Very diverse structure chemistry and functions Hydrophobic or amphipathic Often contain fatty acids sterols or isoprene Functions Energy storage Membranes Cofactors Electron carriers Hormones and other signal molecules Figure 1 7 Page 2 Lipid Structures Properties and Functions 2 Describe the structural features found in common biological fatty acids and relate these to the properties and general functions of fatty acids Fatty Acids Figure 10 2 Figure 10 2 Figure 11 4 see also Figure 2 7 3 General Structure A carboxcylic acid head with a hydrocarbon tail Saturated contain no double bonds in the hydrocarbon tail Monounsaturated contain a single double bond in the hydrocarbon tail usually at C9 almost always cis Polyunsaturated have double bonds separated by a methylene group not conjugated almost always cis of Carbon Atoms 4 to 36 common biological fatty acids range from 12 to 24 fatty acids with an even number of carbon atoms Properties Determined by length and saturation Poorly soluble in water Melting point increases with length and degree of saturation Double bonds cause kinks the prevent packing lowering the melting point Wedge shape causes micell formation Functions Usually part of larger molecules via ester or amide bond Correctly use fatty acid nomenclature draw the structures of palmitate stearate oleate linoleate ALA arachidonate EPA and DHA and interconvert between the structure the carbon skeleton shorthand and the systematic name for common fatty acids Nomenclature Common Names Shorthand carbon skeletons Chain length double bonds bond position from COOH end Systematic names Omega fatty acids Page 3 Lipid Structures Properties and Functions 4 Predict the physical and chemical properties of a fatty acid when given its structure 5 Identify the components found in lipids and classify lipids according to their basic structures and functions Compare and contrast the structural physical and chemical properties of the various lipids and relate these to their biological functions Predict the functions of lipids based on their physical and chemical properties 6 7 Sterols Figure 10 7 Page 4 Lipid Structures Properties and Functions Triacylglycerols Figure 10 7 Structure A glycerol backbone with three fatty acids attached by ester linkages The fatty acids can be the same but are most often different Properties Most abundant lipids in the human body but DO NOT form membranes Hydrophobic stored in anhydrous form Lighter than water F A s attached determine properties liquid or solid at RT Functions Primarily metabolic storage molecules fats in animals oils in plants More reduced carbon provides more energy than carbohydrates Glycogen stores last 24 hrs TAG stores last 2 3 months Insulation Figure 10 3 Page 5 Lipid Structures Properties and Functions Sterols Figure 10 7 Membrane Lipids General Structure Amphipathic Polar head group Phosphodiester Sugar Hydrophobic portion Fatty acids Isoprene derivative Very diverse due to mixing and matching of head groups and tails Backbones Glycerol Sphingosine Figure 11 4 General Properties Membrane lipids are amphipathic Due to cylindrical cross section they form bilayers and liposomes in aqueous solutions Polar heads exposed to aqueous solution Hydrophobic tails buried Page 6 Lipid Structures Properties and Functions Membrane Lipids Figure 10 8 Classes Glycerophospholipids Structure glycerol backbone FA s esterified to C1 and C2 head group attached to C3 by a phosphodiester linkage some have ether linkage to C1 Figure 10 9 Properties different head groups alter properties different fatty acids alter properties C1 often saturated C2 often mono or polyunsaturated Figure 10 14 Function Page 7 major membrane constituent Lipid Structures Properties and Functions Membrane Lipids Classes Glycerophospholipids continued Nomenclature 8 Recognize the structures of common membrane lipid head groups and relate these structures to the properties and functions of the head groups P A P E P C P S P G P I Galactolipids Sulfolipids Structure Glycerol backbone with FA s esterified to C1 and C2 and a head group attached to C3 by a glycosidic linkage Properties Similar to glycerophospholipids Function Abundant in plant chloroplasts Most abundant membrane lipids on the planet May