Phase boundaries and biological membranes. How proteins contribute to phase separation and preferentially distribute into one of the two different phases (or at their interface) is presently unclear. Liquid-ordered assemblies in biomembranes, known as lipid rafts, are small and transient but can coalesce and become stabilized during signalling and vesicle budding. In lipid mixtures, two fluid phases can coexist with different physical properties: liquid-disordered and liquid-ordered. Lipids adopt defined phases depending on their molecular structure and the physical conditions. In most instances, the levels of signalling molecules are exceedingly low compared with the complement of structural lipids that is present in membranes. Several dozen lipids participate in intra- and intercellular signalling processes. ![]() There is clear evidence that several lipids are transported between organelles by non-vesicular mechanisms that involve zones of apposition between donor and acceptor compartments, and macromolecular assemblies that involve multiple lipids and proteins. Lipid transport between and within organelles is poorly understood, but a growing number of genes that are involved in these processes have been unambiguously identified, and their mechanisms of action are under active investigation. In many organelles, the lipid composition of separate leaflets of the membrane bilayer is significantly different, which produces asymmetry across the bilayer - a situation that is maintained by ATP-dependent flippases. Organelles differ both quantitatively and qualitatively in their lipid content. The synthesis of lipids is non-uniformly distributed among a few cellular membranes, which requires most organelles to depend on lipid transport processes to achieve their full complement of lipids. Lipids function as essential structural components of membranes, as signalling molecules, as chemical identifiers of specific membranes and as energy storage molecules. Glycerol with phosphate and an amine group HO-CH2CH2NH3+ CH2O CH CH2-O O- C O -R R- P Ethanolamine HO-CH2CH2N(CH3)3 + Choline HO-CH2CCOO- +NH3 H Phosphatidate OH. ![]() Lipids molecules comprised of more than one component….the individual components are readily disassembled by acid or base hydrolysis Give me some examples Acylglycerols = fatty acids esterified to glycerol -O-C-CH2C-R O Glycerol Monoacylglycerol H R-CH2C-O O H C-OH CH Diacylglycerol HO-O-C-CH2C-R O H Triacylglycerol H (Triglyceride)ġ1 Triacylglycerol Saturated Mono- Unsaturatedġ2 MEMBRANE LIPIDS Glycerophospholipids = 2 fatty acids esterified to 2 D.B.Ĩ Trans Fatty Acids are to be avoided for health reasonsĩ Rule: Double Bonds lower melting point of a fatty acidĬorr: The more double bonds, the lower the melting point Room Temperature Melting Temperature All Unsaturated fats are oils at room temperature 1 2 3 4 D.B. Rule: Double bonds in fatty acids are always CIS C=C H CH2 Rule: Double bonds are always separated by a -CH2- group 9 10 12 H C=C CH2 2 1 11 3 Rule: Double bonds are always numbered 3 apart Example 9,12 means a double bond on C9 and C12ħ Rule: Cis double bonds put Kinks in fatty acid chains.Ĭorr: The more the double bonds the greater the bend Cis D.B. Non-Polar CH3 COO- CH2 Charged carboxyl Methyl end groupĥ Fatty Acids Rule: A lipid begins when water insolubility begins CH3ĬOOH Getting There Not yet Whoa! C12 saturated fatty acid….Lauric acid C14 ….Myristic acid C16….Palmitic acid C18….Stearic acid C20….Arachidic Simple vs Complex Charged vs Neutral Fatty Acids Saturated vs Unsaturated Esterified vs Non-esterified Odd chain vs Even chain Thought for today: If someone calls you a “FAT HEAD”, first compliment them on their biochemical insight, before you punch them in their fat head”.Ģ What is a Lipid? Any substance that is insoluble in water but soluble in organic solvents Does this mean any water insoluble compound? Yes What are some examples I would recognize? Cholesterol….a steroid Stearic acid….a saturated fatty acid Oleic acid…an unsaturated fatty acid Bees wax….a fatty acid ester Vitamins A,D,E,K…the fat-soluble vitamins Tripalmitin…a triacylglycerol Lecithin…a membrane glycerophospholipid ![]() 1 Lipids Classification Properties Function Basic Structure
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