CARBOHYDRATES: STRUCTURES Gropper & Smith, 8th Edition, 2024 Cengage learning, Advanced nutrition and human metabolism, Chapter 3

CHEMICAL STRUCTURE OF CARBOHYDRATES • Molecules containing carbon, hydrogen and oxygen • Produced by plants via photosynthesis • Energy storage (starch) and plant structural tissue (lose) • Saccharides are the building blocks STRUCTURAL CLASSIFICATION OF CARBOHYDRATES Gropper & Smith, 8th Edition, 2022 Cengage learning, Advanced nutrition and human metabolism, Chapter 3 CHEMICAL STRUCTURE OF CARBOHYDRATES Monosaccharides Disaccharides • Simplest carbohydrates • C12 H22O11 • 2 monosaccharides bound together by 5 carbon monosaccharides (pentoses) glycosidic bonds • C5H10O5 • Sucrose = glucose + fructose (alpha 1,2 • Ribose bond) • Deoxyribose • Lactose = glucose + galactose (beta 1,4 bond) 6 carbon monosaccharides (hexoses) • Maltose = glucose + glucose (alpha 1,4 • C6H12O6 bond) • Glucose • Fructose Oligo and polysaccharides • Galactose • (C6 H12 O6)n • Sugar alcohols: xylitol, mannitol and sorbitol • Multiple monosaccharides bound together (= low calorie sweeteners) by alpha 1,4 and alpha 1,6 glycosidic bonds • Starch, fiber and glycogen as storage of carbohydrate in liver and muscle MONOSACCHARIDES: GLUCOSE, FRUCTOSE, GALACTOSE Glucose: • Most abundant monosaccharide • Consumed in food mainly as sucrose ( glucose + fructose): table sugar, molasse, fruit, honey; and as starch of which it is the building block Fructose: • Differs from glucose in that the carbonyl group is on carbon 2 • Is the sweetest monosaccharide = favoured by the food industry as sweetener • Combined to glucose to make sucrose • Found naturally in fruit, honey, vegetables Galactose: • Differs from glucose in the orientation of the OH group at carbon 4 • Is the least sweet of the monosaccharides • Combined with glucose to form the milk sugar lactose • Also present in some plant products: honey, beets, cherries, celery, kiwifruit, soy sauce, plums, and dried figs Byrd-Bredbenner et al. 11th Edition, 2019 McGraw-Hill, Wardlaw’s Perspective in nutrition, Chapter 5 FOOD SOURCES OF GALACTOSE: NOT JUST IN DAIRY Tania Emms, 2005 PENTOSE MONOSACCHARIDES • Ribose and deoxyribose • Contain 5 carbons • Are an essential part of the cell’s genetic material – RNA (ribose) and DNA (2-deoxyribose) • The body makes its own supply from glucose via the pentose phosphate pathway • Also found in food: nuts, meat, dairy, vegetables, and it as part of riboflavin (vitamin B2) Byrd-Bredbenner et al. 11th Edition, 2019 McGraw-Hill, Wardlaw’s Perspective in nutrition, Chapter 5 DISACCHARIDES: SUCROSE, LACTOSE AND MALTOSE • Two monosaccharides linked by a condensation reaction to form alpha or beta glycosidic bonds • Maltose: glucose & glucose with α1,4 glycosidic bond broken by maltase • Lactose: galactose & glucose with β1,4 glycosidic bond broken by lactase • Sucrose: glucose & fructose with α1,2 glycosidic bond broken by sucrase Byrd-Bredbenner et al. 11th Edition, 2019 McGraw-Hill, Wardlaw’s Perspective in nutrition, Chapter 5 SUGAR ALCOHOLS: POLYOLS • Derived from mono-, di- or polysaccharides