BMB 462 1st Edition Lecture 1 Outline of Current Lecture I Definition of a lipid a Defining characteristic b Comparison to other monomers II Fatty Acids Effect of fatty acid structure on function a Trends in changes of fatty acid structure b Using structure to predict properties c Naming Fatty Acids III Triacylglycerols characteristic features a Properties and functions Current Lecture Concepts to remember from previous courses Amino acid structures Van der Waals interactions organic chemistry structures i e Hydrocarbons carboxylates ester bonds 1 Lipids a Definition Cellular molecules that are soluble in organic solvents but not soluble in water b Comparison Unlike other monomers lipids do not have a common structural characteristic The inability to dissolve in water is used to classify molecules as lipids Proteins amino acids have a central C a C group a N group and a R group Carbohydrates contain repeating CH2O units Nucleotides contain a sugarphosphate backbone and a base i Lipids are not true polymers since they do not have a repeating structural unit found in all lipids c Variety in lipid structure results in variety in function i Types of lipids Fatty Acids Triglycerols Steroids Sphingolipids Isoprenoids 2 Fatty Acids a Fatty acids are composed of a polar hydrophilic head group and a nonpolar hydrophobic tail These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute i Fatty acids are typically 12 24 links long though longer fatty acids do exist they are biologically relevant but very rare ii The Polar head is bigger than the nonpolar tail creating a conical shape When free fatty acids are thrown in aqueous solution this conical shape cause the molecules to form a micelle a round cluster of fatty acids that create a hydrophobic interior surrounded by a single polar membrane barrier between the hydrophobic area and the aqueous solution b Adding Carbons to the tail of fatty acids and increasing the degree of unsaturation have big impacts on fatty acid properties i If you add carbons to a fatty acid the melting point increases more Van der Waals interactions require more energy to break the fatty acids apart ii Adding more cis double bonds increasing the degree of unsaturation lowers the melting point more double bonds result in more kinks in the hydrophobic tail which makes it more difficult for fatty acids to pack in tight this is what causes membranes such as those in olive oil to remain liquid at lower temperatures 1 Almost all double bonds are cis Some molecules such as synthetically manufactured ones contain trans double bonds These do not cause a kink in the tail like cis bonds do but they are very rare and bad for health when consumed iii Adding or removing a double bond has a larger affect on fatty acid melting point than adding or removing carbons c Naming fatty acids i Common names there is no real pattern to this common names for fatty acid structures must be memorized ii Shorthand carbon skeletons The first number is the total number of Carbon atoms in the molecule The second number is the number of double bonds When double bonds are present their location is noted by listing the first carbon of the bond in parentheses after the Carbon skeleton name 1 i e 16 1 9 There are 16 carbons and a single double bond which can be found at the 9 carbon a When there is only 1 double bond in a molecule it is typically found at the 9 carbon iii Systematic names This type of naming uses Latin terms denoting the number of carbons and the number of double bonds similar to the Shorthand Carbon Skeleton naming The first part of the name relates to the number of carbons the second part to the number of double bonds and the suffix refers to the type of molecule 1 i e Eicosapentaenoate Eicosa 20 atoms penta 5 double bonds enoate an ester of enoic acid This molecule is an ester with 20 atoms and 5 double bonds iv Omega fatty acids The omega carbon is located in the methyl group at the opposite end of the fatty acid as the carboxyl group Numbering in this fashion the number given is the one at which the first double bond appears 1 i e in an Omega 3 fatty acid the first double bond will be found on the 3 carbon counting 3 in from the end of the tail opposite the polar head group d Triacylglycerols Contain a glycerol back bone and 3 fatty acids acyl fatty acid so triacyl indicates 3 fatty acids i The fatty acids are typically 3 different molecules though on occasion a triacylglycerol contains 3 of the same fatty acid ii Triacylglycerol properties they are the most abundant type of lipid in the body 1 Hydrophobic 2 Lighter than water iii Triacylglycerols are typically energy storage molecules they are not found in membranes 1 Triacylglycerol have 3 months of energy storage compared to 24 hours energy stored in glycogen molecules 2 Their light weight and inability to associate with water makes triacylglycerols ideal storage molecules it is much lighter to store triacylglycerol in the body than to store an energy equivalent amount of glycogen
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