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Understanding Fatty Acids: Structure and Properties

Explore the structures and properties of saturated and unsaturated fatty acids, their melting points, and the role of prostaglandins in the body. Learn about Omega-6 and Omega-3 fatty acids.

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Understanding Fatty Acids: Structure and Properties

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  1. Chapter 17 Lipids 17.2Fatty Acids

  2. Fatty Acids Fatty acids • are long-chain carboxylic acids • typically contain 12 to 18 carbon atoms • are insoluble in water • can be saturated or unsaturated

  3. Fatty Acid Formulas The formulas for fatty acids are written as • condensed structural formulas • line-bond formulas

  4. Saturated Fatty Acids Saturated fatty acids have • single C—C bonds • molecules that fit closely together in a regular pattern • strong attractions between fatty acid chains • high melting points that make them solids at room temperature

  5. Some Saturated Fatty Acids

  6. Unsaturated Fatty Acids Unsaturated fatty acids • have one or more double C═C bond • typically contain cisdouble bonds

  7. Some Unsaturated Fatty Acids

  8. Properties of Unsaturated Fatty Acids Unsaturated fatty acids • have “kinks” in the fatty acid chains • do not pack closely • have fewer attractions between chains • have lower melting points • are liquids at room temperature “kinks” in chain

  9. Learning Check Assign the melting point (mp) of –17 °C, 13 °C, or 69 °C to each one of the following 18-carbon fatty acids, and list the fatty acids in order from highest to lowest mp. Explain. 1) Oleic acid 2) Stearic acid 3) Linoleic acid

  10. Solution Stearic acid is saturated and would have a higher melting point than the unsaturated fatty acids. Oleic acid, which has one double bond, has a higher mp than linoleic oleic acid, which has two double bonds. 2) Stearic acid mp 69°C saturated 1) Oleic acid mp 13°C unsaturated with one double bond 3) Linoleic acid mp -17°C unsaturated with two double bonds

  11. Prostaglandins Prostaglandinshave • 20 carbon atoms in their fatty acid chains • an OH on carbons 11 and 15 • a trans double bond at carbon 13 C11 C15 C13

  12. Omega-6 and Omega-3 Fatty Acids • Fatty acids • in vegetable oils are mostly omega-6 with the first C═C at C6 CH3─(CH2)4─CH═CH─CH2─CH═CH─(CH2)7─COOH 1 6 • Linoleic acid • in fish oils are mostly omega-3 with the first C═C at C3 CH3─CH2─(CH═CH─CH2)3─(CH2)6─COOH • 13 • Linolenic acid

  13. Prostaglandins in the Body Prostaglandins are • produced by injured tissues • involved in pain, fever, and inflammation • not produced when anti-inflammatory drugs such as aspirin inhibit their synthesis

  14. Some Omega-6 and Omega-3 Fatty Acids

  15. Learning Check Draw the condensed structural formula for a fatty acid with 10 carbon atoms that is: A. saturated B. monounsaturated omega-3 C. monounsaturated omega-6

  16. Solution Draw the condensed structural formula for a fatty acid with 10 carbon atoms that is: A. saturated CH3—CH2—CH2—CH2—CH2—CH2—CH2—CH2—CH2—COOH B. monounsaturated omega-3 CH3—CH2—CH═CH—CH2—CH2—CH2—CH2—CH2—COOH C. monounsaturated omega-6 CH3—CH2—CH2—CH2—CH2—CH═CH—CH2—CH2—COOH

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