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Understanding Carbohydrates: Disaccharides and Polysaccharides Overview

Explore the structure and function of disaccharides such as maltose, lactose, and sucrose, as well as polysaccharides like starch, glycogen, and cellulose. Learn about glycosidic bonds and sweetness comparison with sweeteners.

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Understanding Carbohydrates: Disaccharides and Polysaccharides Overview

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  1. Chapter 16 Carbohydrates 16.7 Disaccharides 16.8 Polysaccharides

  2. Disaccharides A disaccharide consists of two monosaccharides. Disaccharide Monosaccharides • Maltose + H2O Glucose + Glucose • Lactose + H2O Glucose + Galactose • Sucrose + H2O Glucose + Fructose

  3. Maltose Maltose is: • A disaccharide in which two D-glucose molecules are joined by an -1,4-glycosidic bond. • Obtained from starch. • Used in cereals, candies, and brewing.

  4. Lactose Lactose is: • Also called milk sugar. • Composed of galactose and glucose linked by a -1,4-glycosidic bond.

  5. Sucrose Sucrose: • Is the disaccharide known as table sugar. • Is composed of glucose and fructose molecules joined by ,-1,2-glycosidic bond. • Has no isomers because mutarotation is blocked.

  6. Sweetness of Sweeteners • Sugars and artificial sweeteners differ in sweetness. • Each sweetener is compared to sucrose (table sugar), which is assigned a value of 100.

  7. Learning Check Identify the monosaccharides in each as 1) glucose, 2) fructose 3) galactose. A. Lactose B. Maltose C. Sucrose

  8. Solution Identify the monosaccharides in each as 1) glucose, 2) fructose 3) galactose. A. Lactose 1) glucose, 3) galactose B. Maltose 1) glucose, 1) glucose C. Sucrose 1) glucose, 2) fructose

  9. Polysaccharides • Polysaccharides are polymers of D-glucose • Important polysaccharides are: Starch (Amylose and Amylopectin) Glycogen Cellulose D-Glucose

  10. Amylose, Amylopectin, and Glycogen • Amylose is a continuous chain of glucose molecules linked by -1,4 glycosidic bonds. • Amylopectin is a branched chain of glucose molecules linked by -1,4- and -1,6-glycosidic bonds. • Glycogen is similar to amylopectin, but more highly branched.

  11. Structures of Amylose and Amylopectin

  12. Cellulose • Cellulose is a polymer of glucose molecules linked by -1,4 glycosidic bonds. • Enzymes in saliva can hydrolyze -1,4 glycosidic bonds in starch, but not -1,4 glycosidic bonds in cellulose.

  13. Learning Check Identify the types of glycosidic bonds in: 1) Amylose 2) Glycogen 3) Cellulose

  14. Solution Identify the types of glycosidic bonds in 1) Amylose-1,4 glycosidic bonds 2) Glycogen-1,4- and -1,6-glycosidic bonds 3) Cellulose-1,4 glycosidic bonds

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