Lecture 18Outline of Last Lecture I. LipidsA. Functions of LipidsII. Fatty AcidsA. Characteristics of Fatty AcidsB. Unsaturated LipidsIII. Essential Fatty AcidsIV. Triacylglycerol Outline of Current Lecture I. TriacylglycerolsA. FunctionII. Trans-fatty AcidsA. CompositionIII. PhosphoacylglycerolsIV. SphingolipidsV. Non-Saponifiable LipidsA. SterolsCurrent LectureThis lecture continues on where we left off with triacylglycerols. These lipids can be densely packed dueto a lack of hydration. They are often used as a storage vessels. Triacylglycerols are a great source of energy. They can be either fats or oils. Their melting point is dependent upon the composition of the esterified fatty acids. They have a high degree of unsaturated carbons, making them liquid at room temperature. Triacylglycerols also do not participate in hydrogen bonding and are non-polar molecules. Triacylglycerols can be chemically modified to act as solids, through the process of hydrogenation. This leads to saturation of any cis-double bonds. When this process is done, trans-fatty acids form as a by- product of the reaction. In a trans-fatty acid, the main difference in structure occurs at the site of the double bond. In cis versions of triacylglycerols, the hydrogen molecules are attached on the same side of the double bond. Trans-fatty acids have hydrogen molecules attached on opposite sides of the double bond. This makes it impossible for our enzymes to degrade trans-fatty acids. Phosphoacylglycerols are another type of lipid. These lipids are found in the lipid membrane. Their structure is centered around phosphatidic acid, which is formed through the esterification of glycerol to two fatty acids and phosphoric acid. These molecules are amphiphilic in nature. They also contain an “X” group thatvaries. The group is always polar or charged in nature.The next type of lipid is called a sphingolipid. These are also a class of membrane lipids. Their core structure is centered around an amino alcohol chain called a sphingosine. The sphingolipid is formed through various linkages. The sphingosine base is amide linked to a fatty acid chain, forming a ceramide. The ceramide BCHM 307 1nd Editionhas a hydroxyl residue attached to it. This residue links with a hydrophilic head group to form the sphingolipid. Sphingolipids are also amphiphilic. Sphingomyelin is a type of sphingolipid that function in the myelin sheath. When the glycolipid isn’t properly degraded in sphingomyelin, this leads to Tay-Sachs disease.The other major category of lipids is non-saponifiable lipids. These lipids do not have ester linkages. Sterols such as cholesterol fall under this category. Cholesterol is another lipid found in lipid membranes. Theseare very hydrophobic molecules. Sterols also function as hormones, such as
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