Reduction of Monosaccharides Monosaccharides can be reduced turning the carbonyl group into an alcohol group. producing sugar alcohols called alditols. and the products named by replacing the - ose ending with -itol. D-Glucose reduces to D-Glucitol, also called D-Sorbitol.
duction of Monosaccharides O O C O O + 2 Pt O C 2 O O O Other artificial sweeteners: xylitol mannitol O O C 2 O D-glucose C 2 O D-glucitol or D-sorbitol
Oxidation of D-Glucose, a Reducing Sugar Glucose is oxidized to a carboxylic acid. Benedict s reagent 2013 Pearson Education, Inc. Chapter 15, Section 2 3
Oxidation of Fructose Fructose, a ketohexose, is also a reducing sugar. In a basic solution such as Benedict's, the carbonyl group moves from carbon 2 to carbon 1, so it can be oxidized as glucose. 2013 Pearson Education, Inc. Chapter 15, Section 2 4
Learning Check Write the products of the oxidation and reduction of D-Mannose. O C O O O O C 2 O D-Mannose 2013 Pearson Education, Inc. Chapter 15, Section 2 5
Solution Write the products of the oxidation and reduction of D-Mannose. O O O O C 2 O Reduction O O C 2 O O O C O O C 2 O Oxidation O O C O O O C 2 O D-Mannitol D-Mannose D-Mannonic acid 2013 Pearson Education, Inc. Chapter 15, Section 2 6
Important Disaccharides A disaccharide consists of two monosaccharides linked together. When two monosaccharides combine in a dehydration reaction, the product is an acetal and water.
Cyclic Acetals Cyclic acetals form when an alcohol adds to a cyclic hemiacetal. are very important in carbohydrate chemistry. It is the type of linkage that bonds glucose molecules to other glucose molecules in the formation of disaccharides and polysaccharides.
Maltose Maltose is a disaccharide also known as malt sugar. used in cereals, candies, and brewing. When maltose in the starches in barley is hydrolyzed by yeast with an enzyme, maltase, two molecules of glucose are obtained. The glucose can undergo fermentation and we have beer. Maltose + 2 O (in barley) maltase glucose + glucose fermentation ethanol (beer)
Formation of Maltose
Lactose Lactose Makes up 6-8% of human milk and 4-5% of cow s milk. People who are lactose intolerant, do not produce enough of the enzyme lactase, which is used to break down lactose. The lactose reaches the colon and is broken down there by bacteria. (this causes discomfort) 2013 Pearson Education, Inc. Chapter 15, Section 1 11
Lactose 2013 Pearson Education, Inc. Chapter 15, Section 1 12
Sucrose Sucrose, or table sugar, is obtained from sugar cane and sugar beets. is hydrolyzed in the body by the enzyme sucrase to form glucose and fructose. It is estimated that each person in the U.S. consumes an average of 150 lbs. of sucrose every year. Sucrose + 2 O sucrase glucose + fructose
Sucrose
Learning Check Draw the aworth structures and give the names of the two monosaccharides that form when sucrose is hydrolyzed.
Solution 2013 Pearson Education, Inc. Chapter 15, Section 2 16
Polysaccharides Polysaccharides are polymers of many monosaccharides linked together. differ in the type of links between monosaccharides, and the monosaccharides in the polymer. differ by the amount of branching in the polymer. 2013 Pearson Education, Inc. Chapter 15, Section 1 17
Important Polysaccharides Important polysaccharides include starches made of -D-glucose molecules, amylose, and amylopectin. glycogen (animal starch in muscle), which is made of -Dglucose. cellulose (plants and wood), which is made of -D-glucose. 2013 Pearson Education, Inc. Chapter 15, Section 1 18
Structures of Amylose and Amylopectin amylose amylopectin
Glycogen Animal starch or glycogen is stored in the liver and muscles of animals. hydrolyzed in our cells to maintain glucose and energy levels between meals. similar to amylopectin, but is more highly branched. 2013 Pearson Education, Inc. Chapter 15, Section 2 20
Cellulose Cellulose is a major structural unit of wood and plants. Cotton is almost pure cellulose. Structure is similar to amylose where the glucose forms a long unbranched chain. The difference is that amylose makes α-1,4-glycosidic bonds and cellulose makes β-1,4- glycosidic bonds. Therefore, cellulose does not coil into a helical shape. 2013 Pearson Education, Inc. Chapter 15, Section 1 21
Cellulose The polysaccharide cellulose is composed of glucose units connected by β-1,4-glycosidic bonds. 2013 Pearson Education, Inc. Chapter 15, Section 1 22
Learning Check Identify the polysaccharides and types of glycosidic bonds in each of the following. A. B. 2013 Pearson Education, Inc. Chapter 15, Section 1 23
Solution Identify the polysaccharides and types of glycosidic bonds in each of the following. A. Cellulose -1,4-glycosidic bonds B. Amylose -1,4-glycosidic bonds Amylopectin -1,4- and -1,6-glycosidic bonds