Chapter09Fall2005 - 1 Chapter 9 - Lipids and Membranes...

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1 Chapter 9 - Lipids and Membranes Lipids are water-insoluble that are either hydrophobic (nonpolar) or amphipathic (polar and nonpolar regions). There are many types of lipids: 1) fatty acids The simplest with structural formula of R-COOH where R = hydrocarbon chain. They differ from each other by the length of the tail, degree of unsaturation, and position of double bonds. pK a of -COOH is 4.5-5.0 --> ionized at physiological pH. If there is no double bond, the fatty acid is saturated. If there is at least one double bond, the fatty acid is unsaturated. Monounsaturated fatty acids contain 1 double bond; polyunsaturated fatty acids have >2 double bonds. IUPAC nomenclature = n represents where double bond occurs as you count from the carboxyl end (see Table 9.1). e.g. -enoate one double bond -dienoate 2 -trienoate 3 -tetraenoate 4 Can also use a colon separating 2 numbers, where the first number represents the number of carbon atoms and the second number indicates the location of the double bonds. e.g. linoleate 18:2 9,12 or cis,cis - 9,12 octadecadienoate Physical properties differ between saturated and unsaturated fatty acids. Saturated = solid at RT; often animal source; e.g. lard Unsaturated = liquid at RT; plant source; e.g. vegetable oil The length of the hydrocarbon tails influences the melting point. As the length of tails increases, melting points increases due to number of van der Waals interactions. Also affecting the melting point is the degree of unsaturation. As the degree of unsaturation increases, fatty acids become more fluid--> melting point decreases ( kinks in tails d number of van der Waals interactions). Fatty acids are also an important sources of energy. 9 kcal/g vs. 4 kcal/g for carbohydrates and proteins. 2)
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Chapter09Fall2005 - 1 Chapter 9 - Lipids and Membranes...

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