Chapter 15 Carbohydrates

Carbohydrates Carbohydrates are A major source of energy from our diet. Composed of the elements C,, and. Also called saccharides, which means sugars. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 2

Carbohydrates Carbohydrates Are produced by photosynthesis in plants. Such as glucose are synthesized in plants from C 2, 2, and energy from the sun. Are oxidized in living cells (respiration) to produce C 2, 2, and energy. Copyright 2007 by Pearson Education, Inc Publishing as Benjamin Cummings 3

Types of Carbohydrates The types of carbohydrates are Monosaccharides, the simplest carbohydrates. Disaccharides, which consist of two monosaccharides. Polysaccharides, which contain many monosaccharides. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 4

Monosaccharides Monosaccharides consist of 3 to 6 carbon atoms, typically. A carbonyl group (aldehyde or ketone). Several hydroxyl groups. 5

Aldoses Aldoses are monosaccharides With an aldehyde group. With many hydroxyl ( ) groups. triose (3 C atoms) tetrose (4 C atoms) pentose (5 C atoms) hexose (6 C atoms) C aldose C C C 2 Erythose, an aldotetrose 6

Ketoses Ketoses are monosaccharides With a ketone group. With many hydroxyl ( ) groups. triose (3 C atoms) tetrose (4 C atoms) pentose (5 C atoms) hexose (6 C atoms) C 2 C= ketose C C C C 2 Fructose, a ketohexose 7

Learning Check Identify each as aldo- or keto- and as tetrose, pentose, or hexose: C 2 C C C C C C C C C 2 C 2 A B 8

Solution A. aldohexose B. ketopentose 9

Fischer Projections 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. Copyright 2007 by Pearson Education, Inc Publishing as Benjamin Cummings 11

D and L Notations 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-isomer. Right is assigned the letter D for the D-isomer. Copyright 2007 by Pearson Education, Inc Publishing as Benjamin Cummings 12

Examples of D and L Isomers of Monosaccharides C C 2 C C 2 C C 2 D-glucose D-ribose L-galactose 13

Learning Check Identify each as the D or L isomer. A. B. C. C C 2 C C 2 C 2 C 2 -ribose - threose - fructose 14

Solution Identify each as the D or L isomer. A. B. C. C C 2 C C L-ribose 2 C L-threose 2 D-fructose C 2 15

D-Glucose D-glucose is Found in fruits, corn syrup, and honey. An aldohexose with the formula C 6 12 6. Known as blood sugar in the body. The monosaccharide in polymers of starch, cellulose, and glycogen. Copyright 2007 by Pearson Education, Inc Publishing as Benjamin Cummings 16

Blood Glucose Level In the body, Glucose has a normal blood level of 70-90 mg/dl. A glucose tolerance test measures blood glucose for several hours after ingesting glucose. Copyright 2007 by Pearson Education, Inc Publishing as Benjamin Cummings 17

D-Fructose D-fructose Is a ketohexose C 6 12 6. Is the sweetest carbohydrate. Is found in fruit juices and honey. Converts to glucose in the body. Copyright 2007 by Pearson Education, Inc Publishing as Benjamin Cummings C 2 C C C C C 2 D-Fructose 18

D-Galactose D-galactose is An aldohexose C 6 12 6. Not found free in nature. btained from lactose, a disaccharide. A similar structure to glucose except for the on C4. C C C C C C 2 D-Galactose 19

Learning Check Draw the structure and Fischer projection of D-fructose. 20

Solution C 2 C C C C C 2 C 2 C= C 2 D-Fructose Fischer projection 21

Cyclic Structures Cyclic structures Are the prevalent form of monosaccharides with 5 or 6 carbon atoms. Form when the hydroxyl group on C-5 reacts with the aldehyde group or ketone group. 23

Cyclic aworth Structures Stable cyclic hemiacetals form When the C= group and the are part of the same molecule. For hexoses, the hydroxyl group on C-5 reacts with the aldehyde group or ketone group. The cyclic structure of a D-isomer has the last C 2 group located above the ring. C 2 24

Drawing the Cyclic Structure for Glucose STEP 1 Number the carbon chain and turn clockwise to form a linear open chain. 1 2 3 4 5 6 C C C C C C 2 C 2 C 6 5 4 3 2 1 C C C C 25

Cyclic Structure for Glucose STEP 2 Bend the chain to make a hexagon Bond the C5 to C1. Place the C6 group above the ring. Write the groups on C2 and C4 below the ring. Write the group on C3 above the ring. Write a new on C1. C 2 6 5 4 1 3 2 26

Cyclic Structure for Glucose (cont) STEP 3 The new on C1 is drawn Down for the α anomer. Up for the β anomer. C 2 C 2 β α α-d-glucose β-d-glucose 27

α-d-glucose and β-d-glucose in Solution When placed in solution, Cyclic structures open and close. α-d-glucose converts to β-d-glucose and back. There is only a small amount of open chain. C 2 C 2 α-d-glucose D-glucose (open) β-d-glucose (36%) (trace) (64%) C C 2 29

Cyclic Structure of Fructose Fructose Is a ketohexose. Forms a cyclic structure. Reacts the on C-5 with the C= on C-2. C 2 C 2 C 2 C 2 C C C C 2 C C 2 D-fructose α-d-fructose β-d-fructose 30

Learning Check Write the cyclic form of α-d-galactose C C C C C C 2 31

Solution C 2 α-d-galactose 32

Reducing Sugars Reducing sugars Are monosaccharides with a carbonyl group that oxidizes to give a carboxylic acid. Undergo reaction with Benedict s reagent (Cu 2+) to give the corresponding carboxylic acid. Include the monosaccharides glucose, galactose, and fructose. 34

xidation of D-Glucose C C C C Benedicts reagent + Cu 2+ [] C C C C Glucose is oxidized to a carboxylic acid + Cu 2 (s) C C 2 C C 2 Cu + (reduced form) D-glucose D-gluconic acid Glucose is a reducing sugar 35

Reduction of Monosaccharides The reduction of monosaccharides Involves the carbonyl group. Produces sugar alcohols called alditols. Such as D-glucose gives D-glucitol also called sorbitol. D-Glucitol Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 36

Learning Check Write the products of the oxidation and reduction of D-mannose. C C 2 D-mannose 37

Solution Write the products of the oxidation and reduction of D-mannose. C 2 C C Reduction xidation C 2 C 2 C 2 D-mannitol D-mannose D-mannonic acid 38

Important Disaccharides A disaccharide Consists of two monosaccharides. Monosaccharides Glucose + glucose Glucose + galactose Glucose + fructose Disaccharide maltose + 2 lactose + 2 sucrose + 2 40

Maltose Maltose is A disaccharide also known as malt sugar. Composed of two D-glucose molecules. btained from the hydrolysis of starch. Linked by an α-1,4-glycosidic bond formed from the α on C1 of the first glucose and on C4 of the second glucose. Used in cereals, candies, and brewing. Found in both the α- and β - forms. 41

Lactose Lactose Is a disaccharide of β- D-galactose and α- or β-d-glucose. Contains a β -1,4- glycosidic bond. Is found in milk and milk products. α-form Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 43

Sucrose Sucrose or table sugar Is obtained from sugar cane and sugar beets. Consists of α-d-glucose and β-d-fructose.. as an α,β-1,2-glycosidic bond. α-d-glucose Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings β-d-fructose 44

Learning Check Write the structures and names of the two monosaccharides that form when sucrose is hydrolyzed. 45

Solution α-d-glucose β-d-fructose 46

Sweeteners Sugars and artificial sweeteners Differ in sweetness. Are compared to sucrose (table sugar), which is assigned a value of 100. TABLE 15.2 60 000 47

Learning Check 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 C. sucrose (1) α-d-glucose (2) β-d-fructose (3) β-d-galactose 48

Solution Identify the monosaccharides in each of the following: A. lactose (1) α-d-glucose (3) β-d-galactose B. maltose (1) α-d-glucose C. sucrose (1) α-d-glucose (2) β-d-fructose 49

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- D-glucose. Include cellulose (plants and wood), which is made of β-d-glucose. C 2 α-d-glucose 51

Amylopectin Amylopectin Is a polymer of α-dglucose molecules. Is a branched-chain polysaccharide. as α-1,4-glycosidic bonds between the glucose units. as α-1,6 bonds to branches. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 54

Glycogen Glycogen Is the polysaccharide that stores α-d-glucose in muscle. Is similar to amylopectin, but is more highly branched. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 55

Cellulose Cellulose Is a polysaccharide of glucose units in unbranched chains. as β-1,4-glycosidic bonds. Cannot be digested by humans because humans cannot break down β-1,4- glycosidic bonds. Copyright 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings 56

Learning Check Identify the polysaccharides and types of glycosidic bonds in each of the following: A. B. C. 57

Solution A. Cellulose β-1,4-glycosidic bonds B. Amylose α-1,4-glycosidic bonds Amylopectin α-1,4-and α-1,6-glycosidic bonds C. Glycogen α-1,4-and α-1,6-glycosidic bonds (more branched than amylopectin) 58