Lipids 5

• Objectives

• Identify a general characteristic of lipids.

• Describe the structure and function of fats.

• Describe the structure and function of steroids.

• Characteristics of LipidsOil's inability to mix with water is typical of the class of water-avoiding compounds called lipids.

• Water-avoiding molecules are said to be hydrophobic, meaning "water-fearing." This property of lipids is important to their function.

• For example, lipids act as a boundary that surrounds and contains the aqueous (watery) contents of your cells.

• FatsA fat consists of a three-carbon backbone called glycerol attached to three fatty acids, which contain long hydrocarbon chains

•Some fats are solid at room temperature. Other fats called oils are liquids at room temperature. In addition to storing energy for later use, fatty tissues cushion your organs and provide your body with insulation.

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• Certain vegetable oils contain unsaturated fat molecules, which have at least one double bond in at least one of the fatty acid chains. In this case, the double bond is located about halfway along the bottom chain

• A saturated fat is a fat in which all three fatty acid chains contain the maximum possible number of hydrogen atoms. In other words, all the carbon atoms in the fatty acid chains form single bonds with each other, and the rest of their bonds are with hydrogen atoms. Most animal fats, such as lard and butter, are saturated. They are solid at room temperature.

• An unsaturated fat, such as the one in Figure 5-9, contains less than the maximum number of hydrogen atoms in one or more of its fatty acid chains because some of its carbon atoms are double-bonded to each other. The fats in fruits, vegetables, and fish are generally unsaturated, as are corn oil, olive oil, and other vegetable oils.

F.Y.I

• Diets rich in saturated fats may be unhealthy. Such diets may promote the buildup of lipid-containing deposits, called plaques, within the walls of blood vessels. These plaques can reduce blood flow and contribute to heart disease.

• SteroidsA lipid molecule in which the carbon skeleton forms four fused rings is called a steroid. While all steroids have a core set of four rings, they differ in the kinds and locations of functional groups attached to the rings.

• Steroids are classified as lipids because they are hydrophobic, but they are very different from fats in structure and function.

• Some steroids circulate in your body as chemical signals. The steroids estrogen, a female sex hormone, and testosterone, a male sex hormone, function in this way

                                                                                                                                 

• . Cholesterol is an essential molecule found in the membranes that surround your cells. It is also the starting point from which your body produces other steroids.

• Despite its necessity, cholesterol has a bad reputation because high levels of particular cholesterol-containing substances in the blood are linked to increased risk for cardiovascular (heart and blood vessel) disease.