Chapter 10: Carbohydrates

Question 1

Define: Cellulose

Answer 1

The most abundant organic molecule in the biosphere

Question 2

Define: Lectins

Answer 2

Carbohydrate-binding proteins

Question 3

Define: Glycosyltransferases

Answer 3

Enzymes that synthesize oligosaccharides

Question 4

Define: Epimers

Answer 4

Monosaccharides that differ at a single asymmetric carbon atom.

Question 5

Define: Starch

Answer 5

The storage form of glucose in plants.

Question 6

Define: Carbohydrates

Answer 6

Has the molecular formula of (CH2O)n.

Question 7

Define: Proteoglycan

Answer 7

Glycoprotein containing glycosaminoglycans

Question 8

Define: Mucoprotein

Answer 8

N-Acetylgalactosamine is a key component of this glycoprotein

Question 9

Define: Glycogen

Answer 9

The storage form of glucose in animals.

Question 10

Indicate whether each of the following pairs of sugars consists of anomers, Epimers, or an Aldose-Ketose pair:

D-glyceraldehyde and dihydroxyacetone

Answer 10

Aldose-ketose

Question 11

Indicate whether each of the following pairs of sugars consists of anomers, Epimers, or an Aldose-Ketose pair:

D-glucose and D-mannose

Answer 11

Epimers

Question 12

Indicate whether each of the following pairs of sugars consists of anomers, Epimers, or an Aldose-Ketose pair:

D-glucose and D-fructose

Answer 12

Aldiss-Ketose

Question 13

Indicate whether each of the following pairs of sugars consists of anomers, Epimers, or an Aldose-Ketose pair:

a-D-glucose and B-D-Glucose

Answer 13

Anomers

Question 14

Indicate whether each of the following pairs of sugars consists of anomers, Epimers, or an Aldose-Ketose pair:

D-ribose and D-ribulose

Answer 14

Aldose-Ketose

Question 15

Indicate whether each of the following pairs of sugars consists of anomers, Epimers, or an Aldose-Ketose pair:

D-galactose and D-Glucose

Answer 15

Epimers

Question 16

Glucose and fructose are reducing sugars. Sucrose, or table sugar, is a disaccharide consisting of both fructose and glucose. Is sucrose a reducing sugar? Explain.

Answer 16

No, sucrose is not a reducing sugar. The anomeric carbon atoms of glucose and fructose can act as the reducing agent, but, in sucrose, the two anomeric carbon atoms are joined by a covalent bond and thus not available to react.

Question 17

Raffinose, a minor constituent in sugar beets, is a trisaccharide.

Is raffinose a reducing sugar? Explain.

Answer 17

Not a reducing sugar, no open-chain forms possible.

Question 18

Raffinose, a minor constituent in sugar beets, is a trisaccharide.

What are the monosaccharides that compose raffinose?

Answer 18

D-Galactose, D-Glucose, and D-Fructose

Question 19

Raffinose, a minor constituent in sugar beets, is a trisaccharide.

B-Glucosidase is an enzyme that will remove galactose residues from an oligosaccharide. What are the products of B-galactosidase treatment of raffinose?

Answer 19

D-Galactose and Sucrose (Glucose + Fructose)

Question 20

A-D-Mannose is a sweet-tasting sugar. B-D-Mannose, on this other hand, tastes bitter. A pure solution of a-D-Mannose loses its sweet taste with time as it is converted into the B-anomer. Draw the B-anomer and explain how it is formed from the a-anomer.

Answer 20

The hemiketal linkage of the a-anomer is broken to form the open form. Rotation about the C-1 and C-2 binds allows the formation of the B-anomer, and a mixture of isomers results.

Question 21

Fructose is in its B-D-pyranose form accounts for the powerful sweetness of honey. The B-D-Furanose form, although sweet, is not as sweet as the pyranose form. The furanose form is the more stable form. Explain why it may not always be wise to cook with honey.

Answer 21

Hearing converts the very sweet pyranose form into the more stable but less sweet furanose form. Consequently, the sweetness of the preparation is difficult to accurately control, which also accounts for why honey loses sweetness with time.

Question 22

Why is the role of glycosaminoglycan in the cushioning provided by cartilage?

Answer 22

The glycosaminoglycan, because it is heavily charged, binds many water molecules. When cartilage is stressed, such as when your heel hits the ground, the water is released, thus cushioning the impact. When you lift your heel, the water rebinds.

Question 23

Define: Enantiomers

Answer 23

Stereoisomers that are mirror images of each other

Question 24

Carbohydrates are:

Answer 24

Aldehydes and ketones with two or more hydroxyl groups.

Question 25

Fructose can cyclize to (a):

Answer 25

both pyranose and furanose ring forms.

Question 26

The nutritional storage form(s) of glucose in plants:

Answer 26

Amylose and Amylopectin

Question 27

To which amino acid residues in glycoproteins are the sugars commonly linked?

Answer 27

Serine, threonine, and asparagine.

Question 28

All of the following are thought to play a role in cancer prevention EXCEPT:

Answer 28

Plants of the order Brassicales hydrolyze glucosinolates and that store organic isothiocyanates as a defense against herbivory.

Question 29

When two carbohydrates are epimers:

Answer 29

They differ only in the configuration around one carbon atom.

Question 30

When forming the disaccharide maltose from two glucose monosaccharides:

Answer 30

Water is eliminated and a hemiacetal is converted to an acetal.

Question 31

Starch and glycogen are both polymers of:

Answer 31

alpha-D-glucose