Carbohydrates. Carbohydrates. Types of Carbohydrates. Aldoses. Monosaccharides Carbohydrates

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1 hapter are a major source of energy from our diet. composed of the elements,, and. also called saccharides, which means sugars. 1 2 are produced by photosynthesis in plants. such as glucose are synthesized in plants from 2, 2, and energy from the sun. are oxidized in living cells to produce 2, 2, and energy. Types of The types of carbohydrates are monosaccharides, the simplest carbohydrates. disaccharides, which consist of two monosaccharides. polysaccharides, which contain many monosaccharides. 3 4 Monosaccharides Aldoses Monosaccharides consist of 3-6 carbon atoms typically. a carbonyl group (aldehyde or ketone). several hydroxyl groups. Aldoses are monosaccharides with an aldehyde group. many hydroxyl (-) groups. triose (3 atoms) tetrose (4 atoms) pentose (5 atoms) hexose (6 atoms) aldose 2 Erythose, an aldotetrose 5 6

2 Ketoses Ketoses are monosaccharides with a ketone group. many hydroxyl (-) groups. 2 = 2 ketose Fructose, a ketohexose Identify each as aldo- or keto- and as tetrose, pentose, or hexose A B 7 8 hapter 14 A. aldohexose B. ketopentose 14.2 Fischer Projections of Monosaccharides 9 10 Fischer Projections D and L Notations A Fischer projection is used to represent carbohydrates. places the most oxidized group at the top. shows chiral carbons as the intersection of vertical and horizontal lines. In a Fischer projection, the group on the chiral carbon farthest from the carbonyl group determines an L or D isomer. left is assigned the letter L for the L-form. right is assigned the letter D for the D-form

3 Examples of D and L Isomers of Monosaccharides D-Glucose D-Ribose L-Galactose Identify each as the D or L isomer. A. B Ribose - Threose - Fructose D-Glucose Identify each as the D or L isomer. A. B L-Ribose L-Threose D-Fructose D-glucose is found in fruits, corn syrup, and honey. an aldohexose with the formula known as blood sugar in the body. the monosaccharide in polymers of starch, cellulose, and glycogen. 2 opyright 2009 by Pearson Education, Inc Blood Glucose Level D-Fructose In the body, glucose has a normal blood level of mg/dl. a glucose tolerance test measures blood glucose for several hours after ingesting glucose. D-Fructose is a ketohexose, is the sweetest carbohydrate. is found in fruit juices and honey. converts to glucose in the body. 2 2 D-Fructose 17 18

4 D-Galactose D-Galactose is an aldohexose, is not found free in nature. is obtained from lactose, a disaccharide. has a similar structure to glucose except for the on carbon 4. 2 D-Galactose Draw the structure of D-fructose hapter D-Fructose 14.3 aworth Structures of Monosaccharides yclic Structures yclic structures are the prevalent form of monosaccharides with 5 or 6 carbon atoms. form when the hydroxyl group on carbon 5 reacts with the aldehyde group or ketone group. Drawing the yclic Structure for Glucose STEP 1: Number the carbon chain and turn clockwise to form a linear open chain

5 yclic Structure for Glucose yclic Structure for Glucose (continued) STEP 2: Fold clockwise to make a hexagon. Bond the carbon 5 to carbon 1. Place the carbon 6 group above the ring. Write the groups on carbon 2 and carbon 4 below the ring. Write the group on carbon 3 above the ring. Write a new on carbon STEP 3: Write the new on carbon 1 down for the α form. up for the β form. 2 α-d-glucose α 2 β-d-glucose β Summary of the Formation of yclic Glucose α-d-glucose and β-d-glucose in When placed in solution, cyclic structures open and close. α-d-glucose converts to β-d-glucose and vice versa. at any time, only a small amount of open chain forms α-d-glucose D-Glucose (open) β-d-glucose (36%) (trace) (64%) yclic Structure of Fructose Fructose is a ketohexose. forms a cyclic structure. reacts the on carbon 5 with the = on carbon D-Fructose α-d-fructose β-d-fructose Write the cyclic form of α-d-galactose. 2 D-Galactose 29 30

6 hapter hemical Properties of Monosaccharides α-d-galactose Reducing Sugars xidation of D-Glucose Reducing sugars are monosaccharides that oxidize to give a carboxylic acid. undergo reaction in the Benedict s test. include the monosaccharides glucose, galactose, and fructose. 2 [] + 2u 2+ (blue) 2 + 2u 2 (red) D-Glucose D-Gluconic acid Reduction of Monosaccharides The reduction of monosaccharides involves the carbonyl group. produces sugar alcohols, or alditols. such as D-glucose gives D-glucitol, also called sorbitol. Write the products of the oxidation and reduction of D-mannose. 2 D-Mannose 35 36

7 hapter 14 Write the products of the oxidation and reduction of D-mannose. 2 2 Reduction 2 xidation 2 D-Mannitol D-Mannose D-Mannonic acid 14.5 Disaccharides Important Disaccharides A disaccharide consists of two monosaccharides. Monosaccharides Disaccharide Glucose + glucose maltose + 2 Glucose + galactose lactose + 2 Glucose + fructose sucrose + 2 Maltose Maltose is a disaccharide also known as malt sugar. composed of two D-glucose molecules. obtained from the hydrolysis of starch. linked by an α-1,4-glycosidic bond formed from the α on carbon 1 of the first glucose and on carbon 4 of the second glucose. used in cereals, candies, and brewing. found in both the α- and β -forms Formation of Maltose Lactose Lactose is a disaccharide of β- D-galactose and α- or β-d-glucose. contains a β -1,4- glycosidic bond. α-form is found in milk and milk products. opyright 2009 by Pearson Education, Inc, 41 42

8 Sucrose Sucrose or table sugar is obtained from sugar cane and sugar beets. consists of α-d-glucose and β-d-fructose. has an α,β-1,2-glycosidic bond. Write the structures of the two monosaccharides that form when sucrose is hydrolyzed. α-d-flucose β D-Fructose Sweetness of Sweeteners Write the structures of the two monosaccharides that form when sucrose is hydrolyzed. Sugars and artificial sweeteners differ in sweetness. are compared to sucrose (table sugar), which is assigned a value of Identify the monosaccharides in each of the following: A. Lactose (1) α-d-glucose (2) β-d-fructose (3) β-d-galactose B. Maltose (1) α-d-glucose (2) β-d-fructose (3) β-d-galactose. Sucrose (1) α-d-glucose (2) β-d-fructose (3) β-d-galactose Identify the monosaccharides in each of the following: A. Lactose (1) α-d-glucose (3) β-d-galactose B. Maltose (1) α-d-glucose. Sucrose (1) α-d-glucose (2) β-d-fructose 47 48

9 hapter 14 Polysaccharides 14.6 Polysaccharides Polysaccharides are polymers of D-glucose. include amylose and amylopectin, starches made of α-d-glucose. include glycogen (animal starch in muscle), which is made of α-dglucose. include cellulose (plants and wood), which is made of β-d-glucose. 2 α-d-glucose Structures of Amylose and Amylopectin Amylose Amylose is a polymer of α-dglucose molecules. linked by α-1,4 glycosidic bonds. a continuous (unbranched) chain Amylopectin Glycogen Amylopectin is a polymer of α-dglucose molecules. is a branched-chain polysaccharide. has α-1,4-glycosidic bonds between the glucose units. has α-1,6 bonds to branches. Glycogen is the polysaccharide that stores α-d-glucose in muscle. is similar to amylopectin, but is more highly branched

10 ellulose ellulose is a polysaccharide of glucose units in unbranched chains. has β-1,4-glycosidic bonds. cannot be digested by humans because humans cannot break down β-1,4- glycosidic bonds. Identify the polysaccharides and types of glycosidic bonds in each of the following. A. B A. ellulose β-1,4-glycosidic bonds B. Amylose α-1,4-glycosidic bonds Amylopectin α-1,4- and α-1,6-glycosidic bonds. Glycogen α-1,4- and α-1,6-glycosidic bonds (more branched than amylopectin) 57