Delphinidin

Lipids are fatty or oily substances that are mostly insoluble in water because they have no polarized components. They typically store about twice as much energy as similar amounts of carbohydrate and play an important role in the longer term energy reserves and structural components of cells. Like carbohydrates, lipid molecules contain carbon, hydrogen, and oxygen, but there is proportionately much less oxygen present.

Examples of lipids include fats, which are solid at room temperature, and oils, which are liquid. An oil molecule is produced when a unit of glycerol—a three-carbon compound that has three hydroxyl (—OH) groups—combines with three fatty acids. A fatty acid has a carboxyl (—COOH) group at one end and typically has an even number of carbon atoms to which hydrogen atoms can become attached.

Most fatty acid molecules consist of a chain with 16 to 18 carbon atoms. If hydrogen atoms are attached to every available bonding site of these fatty acid carbon atoms, as in most animal fats such as butter and those found in meats, the fat is said to be saturated. If there is at least one double bond between two carbons and there are fewer hydrogen atoms attached, the fat is said to be unsaturated. If there are three or more double bonds between the carbons of a fatty acid, as in some vegetable oils such as those of canola, olive, or safflower, the fat is said to be polyunsaturated. Unsaturated vegetable oils can become saturated by bubbling hydrogen gas through them, as is done in the manufacture of margarine.

Human diets high in saturated fats often ultimately lead to clogging of arteries and other heart diseases, while diets low in saturated fats promote better health. However, some fat in the diet appears to be essential to normal animal and human absorption of nutrients, and there is concern that consumption of “fake” fat introduced to the public in the late 1990s could lead to health problems. Like polysaccharides and proteins (discussed in the next section), lipids are broken down by hydrolysis. Waxes are lipids consisting of very long-chain fatty acids bonded to a very long-chain alcohol other than glycerol.

Waxes, which are solid at room temperature, are found on the surfaces of plant leaves and stems. They are usually embedded in a matrix of cutin or suberin, which are also lipid polymers that are insoluble in water. The combinations of wax and cutin or wax and suberin function in waterproofing, reduction of water loss, and protection against microorganisms and small insects. Phospholipids are constructed like fats, but one of the three fatty acids is usually replaced by a phosphate group; this can cause the molecule to become a polarized ion. When phospholipids are placed in water, they form a double-layered sheet resembling a membrane. Indeed, phospholipids are important components of all membranes found in living organisms.