CHEM 17-1 - Ch. 17 – Lipids Fats and oils belong to the...

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Ch. 17 – Lipids Fats and oils belong to the class of biomolecules called lipids. Lipids serve as an energy source or for energy storage (most energy stored in the body is stored in this form), are hormones, are important components of brain and neural tissue, serve as protective insulation for our vital organs, are fat-soluble vitamins (A, D, E, K), and compose cell membranes (phosphoglycerides, sphingolipids, and steroids). Unlike carbohydrates which were categorized by functional group, lipids are classified by solubility, as they are generally insoluble in H 2 O, but soluble in nonpolar organic solvents like hexane, acetone, CH 2 Cl 2 . A general formula for lipids cannot be written. They are subdivided into four main groups: 1) fatty acids, 2) glycerides, 3) nonglyceride lipids, 4) complex lipids. Carboxylic acids (fatty acids) are found as key components in fats and oils, typically contain an even # of C atoms, & are generally unbranched. Fatty acids are classified by the presence and # of C=C bonds. Saturated fatty acids – contain no C=C bonds (see top of Table 17.1, p. 559) Monounsaturated fatty acids – contain one C=C bond Polyunsaturated fatty acids – contain 2 or more C=C bonds Typically unsaturated fatty acids have lower melting points than saturated fatty acids (which are relatively straight and stack closely in a lattice). Does cis- or trans- matter for fatty acids? Inexpensive and abundant vegetable oils (cottonseed, corn, soybean) are converted to oleomargarine and semisolid cooking fats by partial hydrogenation (reaction with H 2 with Ni catalyst). We would be better off using the original vegetable oils, but we prefer the physical consistency and texture of oleo to use of a liquid oil. Most people now try to avoid a diet high in saturated fats (often from animals), which along with cholesterol, will predispose one to the coronary disease arteriosclerosis (hardening of the arteries). Many people switched to margarine to avoid saturated fats, but the
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CHEM 17-1 - Ch. 17 – Lipids Fats and oils belong to the...

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