The Complex Carbohydrates

The simple carbohydrates are the sugars just mentioned: glucose, fructose, and galactose, either singly or paired with glucose. In contrast, the complex carbohydrates contain many glucose units and a few other monosaccharides strung together as polysaccharides. Three are important in nutrition: glycogen, starches, and fibers.

Glycogen is a storage form of energy in the animal body; starches play that role in plants; and the fibers of plants serve as structural elements in stems, trunks, roots, leaves, and skins. Both glycogen and starch are built of glucose units, but they are linked together differently. The fibers are composed of a variety of mono-saccharides and other carbohydrate derivatives.

Glycogen

Glycogen is found only to a limited extent in meats and not at all in plants.* For this reason, glycogen is not a significant food source of carbohydrate, but it does perform an important role in the body. The human body stores much of its glucose as glycogen—many glucose molecules linked together in highly branched chains (see the left side of Figure 4-8). This arrangement permits rapid hydrolysis.

*Glycogen in animal muscles rapidly hydrolyzes after slaughter.

Dorothy Lyman Naomi Harper
Fruits package their simple sugars with fibers, vitamins, and minerals, making them a sweet and healthy snack.

polysaccharide: many monosaccharides linked together.

  • poly = many
  • saccharide = sugar glycogen (GLY-co-gen): an animal polysaccharide composed of glucose; it is manufactured and stored in the liver and muscles as a storage form of glucose. Glycogen is not a significant food source of carbohydrate and is not counted as one of the complex carbohydrates in foods.
  • glyco = glucose
  • gen = gives rise to

Figure 4-8

Glycogen and Starch Molecules Compared (Small Segments)

Notice that the more highly branched the structure, the greater the number of ends from which glucose can be released. (These units would have to be magnified millions of times to appear at the size shown in this figure. For details of the chemical structures, see Appendix C.)

AmylopectinStarch Molecule

Glycogen Starch (amylopectin) Starch (amylose)

A glycogen molecule contains hundreds A starch molecule contains hundreds of glucose molecules in either of glucose units in long, highly branched occasionally branched chains (amylopectin) or unbranched chains chains. (amylose).

Sources Starches
Major sources of starch include grains, legumes, and tubers (such as potatoes, yams, and cassava).

starches: plant polysaccharides composed of glucose.

fibers: in plant foods, the nonstarch polysaccharides that are not digested by human digestive enzymes, although some are digested by GI tract bacteria; fibers include cellulose, hemicelluloses, pectins, gums, and mucilages and the nonpolysaccharides lignins, cutins, and tannins.

Starch

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Responses

  • RUBY HILL
    WHICH FOOD IS NOT A SIGNIFICANT SOURCE OF COMPLEX CARBOHYDRATES?
    5 years ago
  • caoimhe
    Which complex carbohydrate is stored in the fleshy toots of plants such as potatos and yams?
    4 years ago
  • wanda
    Which complex carbohydrate is more highly branched?
    4 years ago
  • nuguse
    Which complex carbohydrate is stored in the fleshy roots of plants such as potatoes and yams?
    3 years ago
  • kaisa
    What form is carbohydrate stored in yam?
    1 year ago

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