Chapter 13 Carbohydrates 13.1 Carbohydrates

Carbohydrates Carbohydrates are a major source of energy from our diet made from elements carbon, hydrogen, and oxygen also called saccharides, which means “sugars”

Carbohydrates 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

Types of Carbohydrates The types of carbohydrates are monosaccharides, the simplest carbohydrates disaccharides, which consist of two monosaccharides polysaccharides, which contain many monosaccharides

Monosaccharides Monosaccharides consist of three to eight carbon chains with one carbon in a carbonyl group are further classified as an aldose, which contains an aldehyde group, or a ketose, which contains a ketone carbonyl group have several hydroxyl groups

Types of Monosaccharides Monosaccharides are also classified by the number of carbon atoms present. triose (3 C atoms) tetrose (4 C atoms) pentose (5 C atoms) hexose (6 C atoms) An aldopentose indicates a five-carbon saccharide with an aldehyde group.

Aldoses O Aldoses are monosaccharides with ║ an aldehyde group C─H aldose HCOH CH2OH Erythose, an aldotetrose Aldoses are monosaccharides with an aldehyde group many hydroxyl (OH) groups

Ketoses Ketoses are monosaccharides with CH2OH a ketone group many hydroxyl (OH) groups CH2OH C=O ketose HCOH Fructose, a ketohexose

Learning Check Identify each as aldo- or keto- and as tetrose, pentose, or hexose. A. B.

Solution Identify each as aldo- or keto- and as tetrose, pentose, or hexose. A. aldohexose B. ketopentose

Fischer Projections of Monosaccharides Chapter 13 Carbohydrates 13.2 Fischer Projections of Monosaccharides

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

D 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

Examples of D and L Isomers of Monosaccharides

Learning Check Identify each as the D or L isomer. A. B. C. __-Ribose __-Threose __-Fructose

Solution Identify each as the D or L isomer. A. B. C. L-Ribose L-Threose D-Fructose

Glucose and Fructose D-glucose is found in fruits, corn syrup, and honey an aldohexose with the formula C6H12O6 known as dextrose and blood sugar in the body D-fructose is obtained from lactose important in cell membranes of the brain and nerve cells

Glucose and Fructose The sweet taste of honey comes from the monosaccharides D-glucose and D-fructose.

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

D-Galactose D-Galactose 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 In a condition called galactosemia, an enzyme needed to convert galactose to glucose is missing.

Learning Check Draw the structure of D-fructose.

Solution

Haworth Structures of Monosaccharides Chapter 13 Carbohydrates 13.3 Haworth Structures of Monosaccharides

Cyclic Structures Cyclic structures are the prevalent form of monosaccharides with five or six carbon atoms form when the hydroxyl group on carbon 5 reacts with the aldehyde group or ketone group

Guide for Drawing Hayworth Structures

Drawing the Cyclic Structure for Glucose Step 1 Number the carbon chain and turn clockwise to form a linear open chain.

Drawing the 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 4 below the ring. Write the –OH group on carbon 3 above the ring. Write a new –OH on carbon 1.

Drawing the Cyclic Structure for Glucose

Drawing the Cyclic Structure for Glucose Step 3 Write the new –OH on carbon 1 down for the  form and up for the  form.

Mutarotation of -D-Glucose and β-D-Glucose in Solution When placed in solution, cyclic structures open and close -D-glucose converts to β-D-glucose and vice versa at any time, only a small amount of open chain forms -D-Glucose D-Glucose (open) β-D-Glucose (36%) (trace) (64%) O H C 2 O H C 2 O H C 2

Cyclic Structure of Fructose is a ketohexose forms a cyclic structure reacts the —OH on carbon 5 with the C=O on carbon 2 O C H 2 D-Fructose α-D-Fructose -D-Fructose

Learning Check Write the cyclic forms of D-galactose.

Solution Step 1 Number the carbon chain and turn clockwise to form a linear open chain. 1 2 3 4 5 6 6 5 4 3 2 1

Solution Step 2 Fold clockwise to make a hexagon. Bond the carbon 5 O to carbon 1 and change the =O to OH on carbon 1. Place the carbon 6 group above the ring. Write the OH groups on carbon 2 and carbon 4 below the ring and the OH group on carbon 3 above the ring.

Solution   Step 3 Write the new –OH on carbon 1 down for the  form or up for the  form.   -D-Galactose -D-Galactose

Chemical Properties of Chapter 13 Carbohydrates 13.4 Chemical Properties of Monosaccharides

Reducing Sugars Reducing sugars are monosaccharides that can be oxidized to give a carboxylic acid contain an aldehyde group in the open chain form undergo reaction in the Benedict’s test include the monosaccharides glucose, galactose, and fructose

Oxidation of D-Glucose

Conversion of Fructose to Glucose Fructose, a ketohexose, is also a reducing sugar. In Benedict’s solution, which is basic, a rearrangement occurs between the ketone group on carbon 2 and the hydroxyl group on carbon 1. This produces an aldehyde group with an adjacent hydroxyl, thereby converting fructose to glucose.

Reduction of Monosaccharides The reduction of monosaccharides produces sugar alcohols, or alditols involves the reduction of the carbonyl group to an alcohol such as D-glucose gives D-glucitol, also called sorbitol

Learning Check Write the products of the oxidation and reduction of D-mannose. D-Mannose

Solution Write the products of the oxidation and reduction of D-mannose. D-Mannitol D-Mannose D-Mannonic acid

Chapter 13 Carbohydrates 13.5 Disaccharides

Important Disaccharides A disaccharide consists of two monosaccharides. Monosaccharides Disaccharide glucose + glucose maltose + H2O glucose + galactose lactose + H2O glucose + fructose sucrose + H2O

Maltose Maltose is a disaccharide also known as malt sugar composed of two D-glucose molecules obtained from the hydrolysis of starch used in cereals, candies, and brewing found in both the  and β forms

Formation of Maltose Maltose is linked by an -1,4-glycosidic bond formed from the  OH on carbon 1 of the first glucose and OH on carbon 4 of the second glucose.

Lactose Lactose is found in milk and milk products is a disaccharide of β-D-galactose and α- or β-D-glucose contains a β-1,4-glycosidic bond

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

Sucrose

Learning Check For the following disaccharide, list the two monosaccharide units and the type of glycosidic bond present.

Solution For the following disaccharide, provide the reaction for two monosaccharide units and the type of glycosidic bond present. galactose + glucose melibiose + H2O The sugar melibiose is formed from two monosaccharides, galactose and glucose, which are joined by a -1,6-glycosidic bond.

Sweetness of Sweeteners Sugars and artificial sweeteners differ in sweetness are compared to sucrose (table sugar), which is assigned a value of 100

Artificial Sweeteners - Sucralose Sucrolose is made from sucrose by replacing some of the hydroxyl groups with chlorine atoms.

Artificial Sweeteners - Aspartame Aspartame is marketed as Nutra-Sweet a noncarbohydrate sweetener made from aspartic acid and a methyl ester of the amino acid phenylalanine

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

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

Chapter 13 Carbohydrates 13.6 Polysaccharides

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 α-D-Glucose

Polysaccharide: Amylose Amylose is a straight-chain polysaccharide made of glucose molecules linked by -1,4 glycosidic bonds

Polysaccharide: Amylopectin Amylopectin, found in plants, is a polymer of α-D-glucose molecules is a branched-chain polysaccharide has α-1,4-glycosidic bonds between the glucose units has α-1,6 bonds to branches

Glycogen Glycogen, or animal starch, is the polysaccharide that stores α-D-glucose in muscle is similar to amylopectin, but is more highly branched the glucose units are joined by α-1,4-glycosidic bonds, and branches occurring about every 10–15 glucose units are attached by α-1,6-glycosidic bonds

Cellulose Cellulose, the major structural unit of wood, 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

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

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

Concept Map for Carbohydrates