20. Carbohydrates

Which disaccharide forms a 1,1-glycosidic linkage?

What is the identity of the disaccharide below?

Draw a disaccharide of two cyclic mannose molecules attached by an α-1,4 glycosidic linkage. Explain why the glycosidic products in Problem 20.58 are not reducing sugars, but the product in this problem is a reducing sugar.

Lactose and maltose are reducing disaccharides, but sucrose is a nonreducing disaccharide. Explain.

Trehalose, a disaccharide found in the blood of insects, has the following structure. What simple sugars would you obtain on hydrolysis of trehalose? (Hint: Rotate one of the rings in your head or redraw it rotated.) <IMAGE>

Are the α and ß forms of the disaccharide lactose enantiomers of each other? Why or why not?

Indicate whether each disaccharide in Problem 13.41 is a reducing sugar or not.

Identify the disaccharide that fits each of the following descriptions: 

a. ordinary table sugar

Isomaltose, obtained from the breakdown of starch, has the following Haworth structure: (13.4, 13.5, 13.6) 

<IMAGE> 

a. Is isomaltose a mono-, di-, or polysaccharide?

Isomaltose, obtained from the breakdown of starch, has the following Haworth structure: (13.4, 13.5, 13.6) <IMAGE>

b. What are the monosaccharides in isomaltose?

Isomaltose, obtained from the breakdown of starch, has the following Haworth structure: (13.4, 13.5, 13.6) <IMAGE>

d. Is this the α or β isomer of isomaltose? 

α−Cellobiose is a disaccharide obtained from the hydrolysis of cellulose. It is quite similar to maltose except it has a β(1→4)−glycosidic bond. Draw the Haworth structure for α−cellobiose. (13.4, 13.6)

For each of the following, give the monosaccharide units produced by hydrolysis, the type of glycosidic bond, and the name of the disaccharide, including α or β:

a. <IMAGE>

The disaccharide trehalose found in mushrooms is composed of two α -d-glucose molecules joined by an α(1→1)−glycosidic bond. Draw the Haworth structure for trehalose. (13.4, 13.6)

Gentiobiose is found in saffron. (13.4, 13.5, 13.6)

b. Is gentiobiose a reducing sugar? Explain.

 What are the disaccharides and polysaccharides present in each of the following? (13.6, 13.7)

a. <IMAGE>

The glycosidic bond in a disaccharide was determined to be α (1→6) . Hydrolysis of the disaccharide produced one galactose and one fructose. Draw the structure of the disaccharide.

ALLIED Health The structure of sucralose, found in the artificial sweetener Splenda, is shown in the figure. It consists of a chlorinated disaccharide made up of galactose and fructose. In its structure shown,

(a) identify the galactose unit and the fructose unit.

<IMAGE>

Trehalose is a naturally occurring disaccharide used in cosmetics because of its ability to retain moisture. The formal name of trehalose is glucose α, α (1→1) glucose. Draw the structure of trehalose. Is it a reducing or nonreducing sugar?

Write the products for the following condensation or hydrolysis reactions:

a. <IMAGE>

ALLIED Health Lactulose is a disaccharide used in the treatment of chronic constipation. Its formal name is galactose ß (1→4) fructose.

(a) Draw the structure of lactulose.

Identify a disaccharide that fits each of the following descriptions:

(a) ordinary table sugar

Isomaltose, a disaccharide formed during caramelization in cooking, contains two glucose units bonded α (1→6) . Draw the structure of isomaltose.

Carbohydrates are abbreviated using a three-letter abbreviation followed by their glycosidic bond type. For example, maltose and sucrose can be written respectively as

Glcα (1→4) Glc Glcα (1→2) ßFru

Maltose Sucrose

Provide the structure for the O-type blood carbohydrate set given the following abbreviation:

L-Fucα (1→2) Galß (1→4) GlcNAc