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Structures of Galactose and Fructose

Galactose has the same structure as glucose except the

Structures of Galactose and Fructose

Ga actose as t e sa e st uctu e as g ucose e cept t econfiguration at carbon four is reversed as shown here.

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Structures of Galactose and Fructose

Galactose is an aldohexose like glucose, and like glucose

Structures of Galactose and Fructose

Galactose is an aldohexose like glucose, and like glucose it also exists in the - and -cyclic pyranose forms.

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Structures of Galactose and Fructose

Fructose is a ketohexose and like glucose it also exists in

Structures of Galactose and Fructose

Fructose is a ketohexose and like glucose it also exists in the open-chain and cyclic forms as shown here. Notice that fructose is a furanose (a five-membered ring). The five-membered ring results because of the position of the keto group in the open chain form.

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Pentoses

D-Ribose and its derivative D-

Pentoses

D Ribose and its derivative D2-deoxyribose are the most important pentoses because p pthey are found in the nucleic acids RNA and DNA.

The 2-deoxy in D-2-deoxyribose means andeoxyribose means an oxygen is omitted from the D-ribose molecule at carbon #2.

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Disaccharides

Disaccharides are carbohydrates consisting of two

Disaccharides

Disaccharides are carbohydrates consisting of two monosaccharide units.

The two monosaccharides are connected by a glycosidic linkage as shown here for the disaccharide lactose .

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Disaccharides

Sucrose and lactose are important disaccharides found in

Disaccharides

Sucrose and lactose are important disaccharides found in the free state in nature.

Sucrose is known as table sugar while lactose is known as milk sugar. Both undergo hydrolysis in the presence of

id h l i lan acid or the enzymes sucrase or lactase, respectively.

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Disaccharides

Maltose is not found in the free state but is the product

Disaccharides

Maltose is not found in the free state but is the product when a polysaccharide is degraded during the sprouting of grain.

Maltose undergoes hydrolysis in the presence of acid or lt t d t l l f lmaltase to produce two molecules of glucose.

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Structures and Properties of DisaccharidesStructures and Properties of Disaccharides

Maltose is derived from two glucose molecules by theMaltose is derived from two glucose molecules by the elimination of a molecule of water between the OH group on carbon 1 of one glucose unit and the OH group of carbon 4 on the other glucose unit.

Thi i 1 4 l idi li k i th l itThis is an -1,4-glycosidic linkage since the glucose units have the -configuration and are joined at carbons 1 and 44.

The structure of maltose is on the following slide . . .g

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Structures and Properties of DisaccharidesStructures and Properties of Disaccharides

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Structures and Properties of Disaccharides

Lactose consists of a -D-galactopyranose unit linked to

Structures and Properties of Disaccharides

Lactose consists of a D galactopyranose unit linked to an -D-glucopyranose unit.

These are joined by a -1,4-glycosidic linkage from carbon 1 on galactose to carbon 4 on glucose.

There are two ways that the -glycosidic linkage in lactose can be drawn (bent or stacked)lactose can be drawn (bent or stacked) . . .

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Structures and Properties of Disaccharides

Bent structureStacked structure

Structures and Properties of Disaccharides

Bent structureStacked structure

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Polysaccharides Derived from Glucose

There are three types of naturally occurring

Polysaccharides Derived from Glucose

There are three types of naturally occurring polysaccharides. They are cellulose, glycogen, and starch that are of major importance.

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Polysaccharides Derived from Glucose

Starch, glycogen, and cellulose all yield D-glucose

Polysaccharides Derived from Glucose

Starch, glycogen, and cellulose all yield D glucose when hydrolyzed.

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Polysaccharides Derived from Glucose

Starch is a polysaccharide found in plants composed of

Polysaccharides Derived from Glucose

Starch is a polysaccharide found in plants composed of amylose and amylopectin.

Amylose is a large molecule consisting of unbranched chains composed of about 25-1300 -D-glucose units j i d b 1 4 l idi li kjoined by -1,4-glycosidic linkages.

Amylopectin is a large molecule with branched chainsAmylopectin is a large molecule with branched chains composed of -1,4-glycosidic linkages in the main chain and -1,6-glycosidic linkages at branch points., g y g p

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Polysaccharides Derived from Glucose

The unbranched structure of amylose.

Polysaccharides Derived from Glucose

The unbranched structure of amylose.

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Polysaccharides Derived from GlucosePolysaccharides Derived from Glucose

The branched structure of amylopectin.The branched structure of amylopectin.

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Polysaccharides Derived from Glucose

An important reaction during digestion is the hydrolysis

Polysaccharides Derived from Glucose

An important reaction during digestion is the hydrolysisof starchy foods as shown below.

Starch is not soluble in cold water due to its large size and will form a colloidal dispersion in hot water.

Starch solutions form a blue black color in the presence ofStarch solutions form a blue-black color in the presence of free iodine.

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Polysaccharides Derived from Glucose

Glycogen is a carbohydrate polymer that is stored in the

Polysaccharides Derived from Glucose

Glycogen is a carbohydrate polymer that is stored in the liver and muscle tissues in animals. It is the energy-storage carbohydrate in animals.

Glycogen has a structure similar to amylopectin except y g y p pthat it is more highly branched with the -1,6-glycosidic linkages occurring more frequently along the polymer chain.

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Polysaccharides Derived from Glucose

Cellulose, like starch and glycogen, is a glucose-based

Polysaccharides Derived from Glucose

Cellulose, like starch and glycogen, is a glucose based polymer.

The glucose units in cellulose are join by -1,4-glycosidic linkages instead of -1,4-glycosidic linkages.

This difference in stereochemistry at the anomeric carbon allows for extensive hydrogen bonding in celluloseallows for extensive hydrogen bonding in cellulose.

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Haworth formulaFigure 27.9 Two representations of

ll l I th thcellulose. In the three-dimensional model note the hydrogen bonding that links the extended cellulose polymers to form cellulose fibersform cellulose fibers.

Three-dimensional model of cellulose

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Polysaccharides Derived from Glucose

Cellulose is the most abundant organic substance found in

Polysaccharides Derived from Glucose

Cellulose is the most abundant organic substance found in nature and it is the chief structural component of plants and wood.