Lipids A Very Fat Chemical Family

The second member of the Royal Carbon Quartet comprise the lipids. The word root, lip, means ''fat,'' while the suffix, -id, means ''belonging to a group.'' [Study suggestion: ''If you're a relative of a lipid, you really need to go on a diet!'' Explain the reasoning behind this comment.]

The lipids are a group of organic molecules that contain many carboncarbon (C—C) and carbon-hydrocarbon (C—H) bonds, so that they are insoluble (in-SAHL-yew-bl) or ''not dissolvable'' in water. There is an old chemical rule-of-thumb that, ''Like dissolves like.'' This means that a solvent having electrically-charged molecules will tend to dissolve a solute with particles that are also electrically charged, because both the solvent and the solute are alike. Take the case of NaCl (sodium chloride) and water (H2O). These two chemicals are very much alike in their electrical charge and

Molecule 5

Molecule 5

chemical bonding. As we saw back in Figure 4.2, the Na+ portion of the NaCl crystal is attracted to the net negative charge on the O2" of the H2O molecules. And the Cl" portion of the NaCl is attracted to the positive charges on each of the H+ poles or ends of the H2O molecule. Hence, the particles of sodium chloride are very soluble (SAHL-yew-bl) or ''dissolvable'' in water, because both chemicals have areas of net (overall) electrical charge.

Now consider, in marked contrast, the chemical anatomy of the body lipids (Figure 4.5). The three main groups in the lipid family are the

Polar phosphate-nitrogen "head"

Fig. 4.5 The three major relatives in the lipid family.

Polar phosphate-nitrogen "head"

Fig. 4.5 The three major relatives in the lipid family.

BASIC STEROID RING STRUCTURE (3 six-carbon rings and 1 five-carbon ring)

BASIC STEROID RING STRUCTURE (3 six-carbon rings and 1 five-carbon ring)

Fig. 4.5 (continued)

Cholesterol within bile crystals

Fig. 4.5 (continued)

triglycerides (try-GLIS-er-eyeds), phospholipids (fahs-foh-LIP-ids), and steroids (STEER-oyds).

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