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.)

Are the α and β 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.

a.

b.

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: 

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

Isomaltose, obtained from the breakdown of starch, has the following Haworth structure:

b. What are the monosaccharides in isomaltose?

Isomaltose, obtained from the breakdown of starch, has the following Haworth structure:

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.

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.

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.

Gentiobiose is found in saffron.

b. Is gentiobiose a reducing sugar? Explain.