Chapter 4 - Chapter 4 The Carbohydrates Sugars Starches and...

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Chapter 4: The Carbohydrates: Sugars, Starches, and Fibers Glucose fuels nearly all of the brain’s activities. Yet, together, these two carbohydrates —glucose and its storage form glycogen—provide about half of all the energy muscles and other body tissues use. The other half comes mostly from fat. People don’t eat glucose and glycogen. When they eat foods rich in carbohydrates, their bodies receive glucose for immediate energy and convert some glucose into glycogen for reserve energy. All plant foods—whole grains, vegetables, legumes, and fruits—provide carbohydrate. Milk also contains carbohydrate. 4.1A A Chemists View The dietary carbohydrate family includes: Monosaccharides: single sugars Disaccharides: sugars composed of pairs of monosaccharides Polysaccharides: large molecules composed of chains of monosaccharides Monosaccharides and disaccharides (the sugars) are sometimes called simple carbohydrates, and polysaccharides (starches and fibers) are sometimes called complex carbohydrates The four main types of atoms found in nutrients are hydrogen (H), oxygen (O), nitrogen (N), and carbon (C). The following list of the most important sugars in nutrition symbolizes them as hexagons and pentagons of different colors. Three are monosaccharides: Glucose, Fructose and Galactose Three are disaccharides: Maltose (glucose + glucose), Sucrose (glucose + fructose) and Lactose (glucose + galactose) 4.1A Monosaccharids The three monosaccharides most important in nutrition all have the same numbers and kinds of atoms—each contains 6 carbon atoms, 12 hydrogens, and 6 oxygens- C6H12O6. The monosaccharides differ in their arrangements of the atoms. These chemical differences account for the differing sweetness of the monosaccharides. Glucose is a larger and more complicated molecule than the ethyl alcohol, but it obeys the same rules of chemistry: each carbon atom has four bonds; each oxygen, two bonds; and each hydrogen, one bond. Commonly known as blood sugar, glucose serves as an essential energy source for all the body’s activities One of these polysaccharides, starch, is the chief food source of energy for all the world’s people; another, glycogen, is an important storage form of energy in the body. Fructose is the sweetest of the sugars. Curiously, fructose has exactly the same chemical formula as glucose—— but its structure differs. Fructose occurs naturally in fruits and honey; other sources include products such as soft drinks, ready-to-eat cereals, and desserts that have been sweetened with high-fructose corn syrup The monosaccharide galactose occurs naturally in foods as a single sugar only in very small amounts. Galactose has the same numbers and kinds of atoms as glucose and fructose in yet another arrangement. Figure 4-3 shows galactose beside a molecule of glucose for comparison.

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