Chapter 16 Carbohydrates

1
Chapter 16 Carbohydrates

• 16.7 Disaccharides
• 16.8 Polysaccharides

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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.

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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.

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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.

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Learning Check

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

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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

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Polysaccharides

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

D-Glucose
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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.

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Structures of Amylose and Amylopectin

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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.

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Learning Check

• Identify the types of glycosidic bonds in
• 1) Amylose
• 2) Glycogen
• 3) Cellulose

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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