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Chapter 14 Carbohydrates Carbohydrates Carbohydrates are • a major source of energy from our diet. • composed of the elements C, H, and O. • also called saccharides, which means “sugars.” 14.1 Carbohydrates 1 Carbohydrates 2 Types of Carbohydrates The types of carbohydrates are • monosaccharides, the simplest carbohydrates. • disaccharides, which consist of two monosaccharides. • polysaccharides, which contain many monosaccharides. Carbohydrates • are produced by photosynthesis in plants. • such as glucose are synthesized in plants from CO2, H2O, and energy from the sun. • are oxidized in living cells to produce CO2, H2O, and energy. Copyright © 2009 by Pearson Education, Inc. 3 4 Aldoses Monosaccharides 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 (-OH) groups. triose (3 C atoms) tetrose (4 C atoms) pentose (5 C atoms) hexose (6 C atoms) O ║ C─H aldose │ H─ C─OH │ H─ C─OH │ CH2OH Erythose, an aldotetrose 5 6 Ketoses Learning Check Ketoses are monosaccharides with • a ketone group. • many hydroxyl (-OH) groups. CH2OH │ C=O Identify each as aldo- or keto- and as tetrose, pentose, or hexose. ketose │ H─ C─OH │ H─ C─OH │ H─C─OH │ CH2OH O CH2OH C H H C OH C O H C OH HO C H H C OH H C OH H C OH CH2OH CH2OH A Fructose, a ketohexose B 7 8 Chapter 14 Solution A. aldohexose Carbohydrates 14.2 Fischer Projections of Monosaccharides B. ketopentose Copyright © 2009 by Pearson Education, Inc. 9 Fischer Projections 10 D 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. and L Notations In a Fischer projection, the −OH 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. Copyright © 2009 by Pearson Education, Inc. 11 12 Examples of D and L Isomers of Monosaccharides H HO Identify each as the D or L isomer. A. B. O O C Learning Check H O OH C H H C OH H OH H OH H OH H OH CH2OH D-Glucose HO H H H H OH H OH HO CH 2OH CH 2OH D-Ribose CH2OH C H H HO H H HO H HO __-Ribose HO OH H H H __- Threose H OH OH CH2OH CH2OH CH2OH L-Galactose O O C H H HO C. O __- Fructose 13 Solution D-Glucose Identify each as the D or L isomer. A. B. D-glucose is • found in fruits, corn syrup, and honey. O H • an aldohexose with C the formula C6H12O6. H C OH • known as blood sugar HO C H in the body. • the monosaccharide in H C OH polymers of starch, H C OH cellulose, and CH2OH glycogen. C. CH2OH O C H H HO H H HO H HO CH2OH L-Ribose O O C H HO 14 HO OH H H H CH2OH L-Threose H OH OH CH2OH D-Fructose Copyright © 2009 by Pearson Education, Inc. 15 Blood Glucose Level 16 D-Fructose 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. D-Fructose • is a ketohexose, C6H12O6. • is the sweetest carbohydrate. • is found in fruit juices and honey. • converts to glucose in the body. CH2OH C O HO H H H OH OH CH2OH D-Fructose Copyright © 2009 by Pearson Education, Inc. Copyright © 2009 by Pearson Education, Inc. 17 18 D-Galactose Learning Check D-Galactose Draw the structure of D-fructose. O • is an aldohexose, C6H12O6. • is not found free in nature. • is obtained from lactose, a disaccharide. • has a similar structure to glucose except for the –OH on carbon 4. C H H OH HO H HO H H OH CH2OH D-Galactose 19 Solution 20 Chapter 14 14.3 Haworth Structures of Monosaccharides CH2OH C O HO H H OH H OH Carbohydrates CH2OH O CH2OH OH OH OH D-Fructose OH 21 Drawing the Cyclic Structure for Glucose Cyclic Structures STEP 1: Number the carbon chain and turn clockwise to form a linear open chain. Cyclic structures • are the prevalent form of monosaccharides with 5 or 6 carbon atoms. O 22 H O C O 1 H C OH H 2 HO 3C H • form when the hydroxyl group on carbon 5 reacts with the aldehyde group or ketone group. H 4C OH H 5C OH H OH H O HOCH 2 C C C C C 6 5 4 3 2 1 H OH OH H OH 6CH2OH 23 24 Cyclic Structure for Glucose (continued) Cyclic Structure for Glucose STEP 2: Fold clockwise to make a hexagon. • Bond the carbon 5 –O– to carbon 1. • Place the carbon 6 group above the ring. • Write the –OH groups on carbon 2 and carbon 4 below the ring. • Write the –OH group on carbon 3 above the ring. • Write a new –OH on carbon 1. STEP 3: Write the new –OH on carbon 1 • down for the α form. • up for the β form. CH2OH 6 O CH2OH 5 4 OH 1 OH 3 CH2OH O OH 2 OH OH OH O OH OH OH α β OH OH OH α-D-Glucose β-D-Glucose 25 26 α-D-Glucose and β-D-Glucose in Summary of the Formation of Cyclic Glucose Solution 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. CH2OH CH2OH O OH OH OH OH α-D-Glucose H OH OH Copyright © 2009 by Pearson Education, Inc. D-Glucose (36%) (open) (trace) 27 Cyclic Structure of Fructose C O CH2OH HO C H CH2OH D-Fructose CH2OH α-D-Fructose (64%) 28 O O C H H HO HO OH H CH2OH OH OH OH β-D-Glucose Write the cyclic form of α-D-galactose. OH OH H C OH H C OH CH2OH O OH OH OH Learning Check Fructose • is a ketohexose. • forms a cyclic structure. • reacts the —OH on carbon 5 with the C=O on carbon 2. CH2OH O O C OH CH2OH H O OH OH H H OH CH2OH D-Galactose β-D-Fructose 29 30 Chapter 14 Solution 14.4 Chemical Properties of Monosaccharides CH2OH O OH Carbohydrates OH OH OH α-D-Galactose Copyright © 2009 by Pearson Education, Inc. 31 32 Oxidation of D-Glucose Reducing Sugars 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. O O C OH C H H C OH H C OH HO H H H OH OH + 2Cu2+ [O] HO H (blue) H H OH OH + 2Cu2O (red) CH2OH CH2OH D-Gluconic acid D-Glucose 33 Reduction of Monosaccharides 34 Learning Check Write the products of the oxidation and reduction of D-mannose. The reduction of monosaccharides • involves the carbonyl group. • produces sugar alcohols, or alditols. • such as D-glucose gives D-glucitol, also called sorbitol. O C H HO H HO H H H OH OH CH2OH D-Mannose Copyright © 2009 by Pearson Education, Inc. 35 36 Solution Chapter 14 Carbohydrates Write the products of the oxidation and reduction of D-mannose. O O HO H HO H H H C OH C H CH2OH Reduction HO H HO H OH H OH H Oxidation HO D-Mannitol OH H OH H D-Mannose H HO H OH OH CH2OH CH2OH CH2OH 14.5 Disaccharides D-Mannonic acid Copyright © 2009 by Pearson Education, Inc. 37 Important Disaccharides 38 Maltose Maltose is A disaccharide consists of two monosaccharides. Monosaccharides Disaccharide Glucose + glucose maltose + H2O Glucose + galactose lactose + H2O Glucose + fructose sucrose + H2O • • • • 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 −OH on carbon 1 of the first glucose and −OH on carbon 4 of the second glucose. • used in cereals, candies, and brewing. • found in both the α- and β -forms. 39 Formation of Maltose 40 Lactose Lactose • is a disaccharide of βD-galactose and α- or β-D-glucose. • contains a β -1,4glycosidic bond. • is found in milk and milk products. α-Form Copyright © 2009 by Pearson Education, Inc, Copyright © 2009 by Pearson Education, Inc. 41 42 Sucrose Learning Check 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 Copyright © 2009 by Pearson Education, Inc. β –D-Fructose 43 Solution 44 Sweetness of Sweeteners Sugars and artificial sweeteners Write the structures of the two monosaccharides that form when sucrose is hydrolyzed. • differ in sweetness. • are compared to sucrose (table sugar), which is assigned a value of 100. Copyright © 2009 by Pearson Education, Inc. 45 46 Learning Check Solution Identify the monosaccharides in each of the following: A. Lactose (3) β-D-Galactose (1) α-D-Glucose (2) β-D-Fructose Identify the monosaccharides in each of the following: A. Lactose (1) α-D-Glucose (3) β-D-Galactose B. Maltose (1) α-D-Glucose (2) β-D-Fructose (3) β-D-Galactose B. Maltose (1) α-D-Glucose C. Sucrose (1) α-D-Glucose (2) β-D-Fructose (3) β-D-Galactose C. Sucrose (1) α-D-Glucose 47 (2) β-D-Fructose 48 Chapter 14 Carbohydrates 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. 14.6 Polysaccharides CH2OH O OH OH OH OH α-D-Glucose Copyright © 2009 by Pearson Education, Inc. 49 Structures of Amylose and Amylopectin 50 Amylose Amylose is • a polymer of α-Dglucose molecules. • linked by α-1,4 glycosidic bonds. • a continuous (unbranched) chain. Copyright © 2009 by Pearson Education, Inc. 51 Amylopectin 52 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. Copyright © 2009 by Pearson Education, Inc. Copyright © 2009 by Pearson Education, Inc. 53 54 Cellulose Learning Check Identify the polysaccharides and types of glycosidic bonds in each of the following. Cellulose • 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-1,4glycosidic bonds. A. B. C. Copyright © 2009 by Pearson Education, Inc. Copyright © 2009 by Pearson Education, Inc. 55 Solution A. Cellulose β-1,4-glycosidic bonds B. Amylose Amylopectin α-1,4-glycosidic bonds α-1,4- and α-1,6-glycosidic bonds C. Glycogen α-1,4- and α-1,6-glycosidic bonds (more branched than amylopectin) 57 56