Introduction to General, Organic and Biochemistry

Frederick A. Bettelheim, William H. Brown, Mary K. Campbell

Chapter 20

Carbohydrates - all with Video Answers

Educators

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Chapter Questions

Problem 1

Draw Fischer projections for all 2-ketopentoses. Which are D-2-ketopentoses, which are $1-2$ -ketopentoses, and which are enantiomers? Refer to Table 20.2 and write the name of each 2 -ketopentose.

Ummatul Choudary

Ummatul Choudary

Numerade Educator

Problem 2

D-Mannose exists in aqueous solution as a mixture of $\alpha$ -D-mannopyranose and $\beta$ -D-mannopyranose. Draw Haworth projections for these molecules.

Ummatul Choudary

Ummatul Choudary

Numerade Educator

Problem 3

Draw chair conformations for $\alpha$ -D-mannopyranose and $\beta$ -D-mannopyranose. Label the anomeric carbon in each.

Ummatul Choudary

Ummatul Choudary

Numerade Educator

Problem 4

Draw a Haworth projection and a chair conformation for methyl $\alpha$ -D-mannopyranoside (methyl $\alpha$ -D-mannoside). Label the anomeric carbon and the glycosidic bond.

Danielle Ashley

Danielle Ashley

Numerade Educator

Problem 5

Draw a chair conformation for the $\alpha$ form of a disaccharide in which two units of D-glucopyranose are joined by a $\beta-1,3$ -glycosidic bond.

Danielle Ashley

Danielle Ashley

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Problem 6

Define carbohydrate.

Shalini Tyagi

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Problem 7

What is the difference in structure between an aldose and a ketose? Between an aldopentose and a ketopentose?

Megha Ramappan

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Problem 8

Of the eight $\mathrm{D}$ -aldohexoses, which is the most abundant in the biological world?

Megha Ramappan

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Problem 9

Name the three most abundant hexoses in the biological world. Which are aldohexoses, and which are ketohexoses?

Megha Ramappan

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Problem 10

Which hexose is also known as "dextrose"?

Megha Ramappan

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Problem 11

What does it mean to say that $\mathrm{D}$ - and I-glyceraldehyde are enantiomers?

Megha Ramappan

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Problem 12

Explain the meaning of the designations $D$ and $\mathrm{L}$ as used to specify the configuration of a monosaccharide.

Megha Ramappan

Numerade Educator

Problem 13

Which carbon of an aldopentose determines whether the pentose has a $\mathrm{D}$ or $\mathrm{L}$ configuration?

Ummatul Choudary

Ummatul Choudary

Numerade Educator

Problem 14

How many stereocenters are present in $\mathrm{D}$ -glucose? In $D$ -ribose? How many stereoisomers are possible for each monosaccharide?

Megha Ramappan

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Problem 15

Which of the following compounds are D-monosaccharides, and which are L-monosaccharides?

Megha Ramappan

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Problem 16

Draw Fischer projections for L-ribose and L-arabinose.

Megha Ramappan

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Problem 17

Draw a Fischer projection for a $\mathrm{D}$ - 2 -ketoheptose.

Megha Ramappan

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Problem 18

Explain why all mono- and disaccharides are soluble 20
in water.

Megha Ramappan

Numerade Educator

Problem 19

What is an amino sugar? Name the three amino sugars most commonly found in nature.

Ummatul Choudary

Ummatul Choudary

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Problem 20

Define the term anomeric carbon. Which carbon is the anomeric carbon in glucose? In fructose?

Megha Ramappan

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Problem 21

Define (a) pyranose and (b) furanose.

Ummatul Choudary

Ummatul Choudary

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Problem 22

Explain the conventions for using $\alpha$ and $\beta$ to designate the configurations of the cyclic forms of monosaccharides.

Catherine M.

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Problem 23

Are $\alpha$ -D-glucose and $\beta$ -D-glucose anomers? Explain. Are they enantiomers? Explain.

Emily Himsel

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Problem 24

Are the hydroxyl groups on carbons $1,2,3,$ and 4 of $\alpha$ -D-glucose all in equatorial positions?

Ummatul Choudary

Ummatul Choudary

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Problem 25

In what way are chair conformations a more accurate representation of the molecular shapes of hexopyranoses than Haworth projections?

Emily Himsel

Numerade Educator

Problem 26

Convert each of the following Haworth projections to an open-chain form and to a Fischer projection. Name the monosaccharides you have drawn.

Danielle Ashley

Danielle Ashley

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Problem 27

Convert each of the following chair conformations to an open-chain form and to a Fischer projection. Name the monosaccharides you have drawn.

Danielle Ashley

Danielle Ashley

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Problem 28

Explain the phenomenon of mutarotation. How is it detected?

Alexander Burbelo

Alexander Burbelo

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Problem 29

The specific rotation of $\alpha$ -D-glucose is $+112.2^{\circ} .$ What is the specific rotation of $\alpha$ -L-glucose?

Alexander Burbelo

Alexander Burbelo

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Problem 30

When $\alpha$ -D-glucose is dissolved in water, the specific rotation of the solution changes from $+112.2^{\circ}$ to $+52.7^{\circ} .$ Does the specific rotation of $\alpha$ -L-glucose also change when it is dissolved in water? If so, to what value does it change?

Alexander Burbelo

Alexander Burbelo

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Problem 31

Define the terms glycoside and glycosidic bond.

Ummatul Choudary

Ummatul Choudary

Numerade Educator

Problem 32

What is the difference in meaning between the terms glycosidic bond and glucosidic bond?

Noah Boudrie

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Problem 33

Do glycosides undergo mutarotation?

Alexander Burbelo

Alexander Burbelo

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Problem 34

Draw Fischer projections for the product formed by treating each of the following monosaccharides with sodium borohydride, $\mathrm{NaBH}_{4}$, in water
(a) D-Galactose
(b) D-Ribose

Sana Riaz

Numerade Educator

Problem 35

Reduction of D-glucose by NaBH gives D-sorbitol, a compound used in the manufacture of sugar-free gums and candies. Draw a structural formula for D-sorbitol.

Emily Himsel

Numerade Educator

Problem 36

Reduction of D-fructose by $\mathrm{NaBH}_{4}$ gives two alditols, one of which is D-sorbitol. Name and draw a structural formula for the other alditol.

Ummatul Choudary

Ummatul Choudary

Numerade Educator

Problem 37

Ribitol and $\beta$ -D-ribose 1 -phosphate are derivatives of D-ribose. Draw a structural formula for each compound.

Alexander Burbelo

Alexander Burbelo

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Problem 38

Name three important disaccharides. From which monosaccharides is each derived?

Ronald Prasad

Numerade Educator

Problem 39

What does it mean to describe a glycosidic bond as $\beta-1,4-?$ To describe it as $\alpha-1,6-?$

Sana Riaz

Numerade Educator

Problem 40

Both maltose and lactose are reducing sugars, but sucrose is a nonreducing sugar. Explain why.

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Morgan Ovil

Numerade Educator

Problem 41

Following is a structural formula for a disaccharide.
(a) Name the two monosaccharide units in the disaccharide.
(b) Describe the glycosidic bond.
(c) Is this disaccharide a reducing sugar or a nonreducing sugar?
(d) Will this disaccharide undergo mutarotation?

Ummatul Choudary

Ummatul Choudary

Numerade Educator

Problem 42

The disaccharide trehalose is found in young mushrooms and is the chief carbohydrate in the blood of certain insects.
(a) Name the two monosaccharide units in trehalose.
(b) Describe the glycosidic bond in trehalose.
(c) Is trehalose a reducing sugar or a nonreducing sugar?
(d) Will trehalose undergo mutarotation?

Sana Riaz

Numerade Educator

Problem 43

What is the difference in structure between oligosaccharides and polysaccharides?

Catherine M.

Numerade Educator

Problem 44

Name three polysaccharides that are composed of units of D-glucose. In which polysaccharide are the glucose units joined by $\alpha$ -glycosidic bonds? In which are they joined by $\beta$ -glycosidic bonds?

Sana Riaz

Numerade Educator

Problem 45

Starch can be separated into two principal polysaccharides, amylose and amylopectin. What is the major difference in structure between the two?

Sana Riaz

Numerade Educator

Problem 46

Where is glycogen stored in the human body?

Christian Daniele

Christian Daniele

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Problem 47

Why is cellulose insoluble in water?

Catherine M.

Numerade Educator

Problem 48

How is it possible that cows can digest grass but humans cannot?

Emily Himsel

Numerade Educator

Problem 49

A Fischer projection of $N$ -acetyl-D-glucosamine is given in Section $20.1 \mathrm{D}$.
(a) Draw a Haworth projection and a chair conformation for the $\beta$ -pyranose form of this monosaccharide.
(b) Draw a Haworth projection and a chair conformation for the disaccharide formed by joining two units of the pyranose form of $N$ -acetyl-Dglucosamine with a $\beta-1,4$ -glycosidic bond. If you draw them correctly, you will have a structural formula for the repeating dimer of chitin, the structural polysaccharide component of the shell of lobsters and other crustaceans.

Sana Riaz

Numerade Educator

Problem 50

Propose structural formulas for the repeating disaccharide unit in these polysaccharides.
(a) Alginic acid, isolated from seaweed, is used as a thickening agent in ice cream and other foods. Alginic acid is a polymer of D-mannuronic acid in the pyranose form joined by $\beta-1,4$ -glycosidic bonds.
(b) Pectic acid is the main component of pectin, which is responsible for the formation of jellies from fruits and berries. Pectic acid is a polymer of D-galacturonic acid in the pyranose form joined by $\alpha-1,4$ -glycosidic bonds.

Sana Riaz

Numerade Educator

Problem 51

Hyaluronic acid acts as a lubricant in the synovial fluid of joints. In rheumatoid arthritis, inflammation breaks hyaluronic acid down to smaller molecules. Under these conditions, what happens to the lubricating power of the synovial fluid?

Sana Riaz

Numerade Educator

Problem 52

The anticlotting property of heparin is partly due to the negative charges it carries.
(a) Identify the functional groups that provide the negative charges.
(b) Which type of heparin is a better anticoagulant, one with a high degree or a low degree of polymerization?

Sana Riaz

Numerade Educator

Problem 53

(Chemical Connections $20 \mathrm{A}$ ) Why does congenital galactosemia appear only in infants? Why can galactosemia be relieved by feeding an affected infant a formula containing sucrose as the only carbohydrate?

Emily Himsel

Numerade Educator

Problem 54

(Chemical Connections $20 \mathrm{B}$ ) What is the difference in structure between $\mathrm{L}$ -ascorbic acid and $\mathrm{L}$ -dehydroascorbic acid? What does the designation $\mathrm{L}$ indicate in these names?

Emily Himsel

Numerade Educator

Problem 55

(Chemical Connections $20 \mathrm{B}$ ) When L-ascorbic acid participates in a redox reaction, it is converted to L-dehydroascorbic acid. In this reaction, is L-ascorbic acid oxidized or reduced? Is L-ascorbic acid a biological oxidizing agent or a biological reducing agent?

Emily Himsel

Numerade Educator

Problem 56

(Chemical Connections $20 \mathrm{C}$ ) Why is the glucose assay one of the most common analytical tests performed in clinical chemistry laboratories?

Emily Himsel

Numerade Educator

Problem 57

(Chemical Connections 20 D) What monosaccharides do types $A, B,$ and $O$ blood have in common? In which monosaccharides do they differ?

Emily Himsel

Numerade Educator

Problem 58

(Chemical Connections $20 \mathrm{D}$ ) L-Fucose is a monosaccharide unit common to $\mathrm{A}, \mathrm{B}, \mathrm{AB},$ and $\mathrm{O}$ blood types.
(a) Is this monosaccharide an aldose or a ketose? A hexose or a pentose?
(b) What is unusual about this monosaccharide?
(c) If $t$ -fucose were to undergo a reaction in which its terminal $-\mathrm{CH}_{3}$ group was converted to a $-\mathrm{CH}_{2} \mathrm{OH}$ group, which monosaccharide would result?

Sana Riaz

Numerade Educator

Problem 59

(Chemical Connections 20 D) Why can't a person with type A blood donate to a person with type B blood?

Emily Himsel

Numerade Educator

Problem 60

(Chemical Connections $20 \mathrm{E}$ ) Low-fat and lowcarbohydrate diets can both produce weight loss. Are there any health-related differences in the outcomes of the two kinds of diets? Explain.

Emily Himsel

Numerade Educator

Problem 61

$2,6-$ Dideoxy-D-altrose, also known as D-digitoxose, is a monosaccharide obtained from the hydrolysis of digitoxin, a natural product extracted from purple foxglove (Digitalis purpurea). Digitoxin has found wide use in cardiology because it reduces pulse rate, regularizes heart rhythm, and strengthens heartbeat. Draw a structural formula for the open-chain form of 2,6 -dideoxy-D-altrose.

Sana Riaz

Numerade Educator

Problem 62

In making candy or sugar syrups, sucrose is boiled in water with a little acid, such as lemon juice. Why does the product mixture taste sweeter than the initial sucrose solution?

Emily Himsel

Numerade Educator

Problem 63

Hot-water extracts of ground willow bark are an effective pain reliever (Chemical Connections $19 \mathrm{C}$ ). Unfortunately, the liquid is so bitter that most people refuse it. The pain reliever in these infusions is salicin. Name the monosaccharide unit in salicin.

Emily Himsel

Numerade Educator

Problem 64

Show how D-sorbitol, used in "sugarless" chewing gum, is produced from D-glucose.

Emily Himsel

Numerade Educator

Problem 65

Carbohydrates in most foods have roughly the same molecular weight. True or false?

Sana Riaz

Numerade Educator

Problem 66

Ribose and fructose have an important similarity in structure in that they both have five-membered rings. How do they differ in structure?

Catherine M.

Numerade Educator

Problem 67

In Section $20.4 \mathrm{A}$, two structures are shown for sucrose. In one, both the glucose and fructose moieties are shown in the Haworth representation. In the other, the chair form of the glucose moiety is shown with a glycosidic bond to the fructose moiety shown in the Haworth form. Why does the Haworth form for the fructose moiety appear in both structures?

Sana Riaz

Numerade Educator

Problem 68

Blood samples for research or medical tests sometimes have heparin added. Why is this done?

Sam Limsuwannarot

Sam Limsuwannarot

Numerade Educator

Problem 69

What is the difference in the glycosidic bonds in starch and cellulose? How does this difference affect their biological function?

Sana Riaz

Numerade Educator

Problem 70

What are the structural differences between vita$\min \mathrm{C}$ and sugars? Do these structural differences play a role in the susceptibility of this vitamin to air oxidation?

Emily Himsel

Numerade Educator

Problem 71

A substance called laetrile is structurally related to carbohydrates. It has been suggested as a treatment for cancer, but it is not available in the United States. Its efficacy is doubtful, and it is inherently dangerous. Here is the structure. What is its relationship to carbohydrates? Do you think that the presence of the cyanide ( $-\mathrm{CN}$ ) group in the structure has a connection to the dangers associated with this compound? Explain.

Sana Riaz

Numerade Educator

Problem 72

Why are five- and six-membered rings encountered more frequently than any other possible ring size in the cyclic structures of sugars?

Sana Riaz

Numerade Educator

Problem 73

What is the structural difference between glucose and galactose? Is it possible that galactose could be converted to glucose in the body? If so, what kind of process takes place?

Sana Riaz

Numerade Educator

Problem 74

Concentrated sulfuric acid can be used as a highly effective dehydrating agent. When concentrated sulfuric acid is added to a beaker that contains sucrose, the white powder reacts, leaving behind a black substance that is mostly carbon. What sort of reaction has taken place?

Emily Himsel

Numerade Educator

Problem 75

Chitin is a polysaccharide found in shrimp and lobster shells. It is a polymer of $N$ -acetyl-Dglucosamine, where the bonding between monomer units is a $\beta-1,4$ -glycosidic bond. Propose a structure for chitin.

Sana Riaz

Numerade Educator

Problem 76

In Section $20.2,$ we saw that in glucose, all atoms other than hydrogen are in the stable equatorial position. Suggest a correlation between the structure of glucose and its central role in the structure and function of carbohydrates.

Sana Riaz

Numerade Educator

Problem 77

One pathway for the metabolism of D-glucose- 6 phosphate is its enzyme-catalyzed conversion to D-fructose- -6-phosphate. Show that this transformation can be regarded as two enzyme-catalyzed keto-enol tautomerizations (Section 17.5 ).

Sana Riaz

Numerade Educator

Problem 78

One step in glycolysis, the pathway that converts glucose to pyruvate (Section 28.2 ), involves an enzyme-catalyzed conversion of dihydroxyacetone phosphate to D-glyceraldehyde 3 -phosphate. Show that this transformation can be regarded as two enzyme-catalyzed keto-enol tautomerizations (Section 17.5 ).

Sana Riaz

Numerade Educator

Problem 79

Following is a Haworth projection and a chair conformation for the repeating disaccharide unit in chondroitin 6 -sulfate. This biopolymer acts as the flexible connecting matrix between the tough protein filaments in cartilage. It is available as a dietary supplement, often combined with $\mathrm{D}$ -glucosamine sulfate. Some believe this combination can strengthen and improve joint flexibility.
(a) From what two monosaccharide units is the repeating disaccharide unit of chondroitin 6-sulfate derived?
(b) Describe the glycosidic bond between the two units.

Sana Riaz

Numerade Educator

Problem 80

Below is the structural formula of coenzyme $A,$ an important biomolecule.
(a) Is coenzyme A chiral? (Chapter 15 )
(b) Name each functional group in coenzyme A. (Chapter $10)$
(c) Would you expect coenzyme A to be soluble in water? Explain. (Chapter 5 )
(d) Draw structural formulas for the products of complete hydrolysis of coenzyme A in aqueous HCI. Show each product as it would be ionized in this solution. (Chapter 19 )
(e) Draw structural formulas for the products of complete hydrolysis of coenzyme A in aqueous NaOH. Show each product as it would be ionized in this solution. (Chapter 19 )

Danielle Ashley

Danielle Ashley

Numerade Educator

Problem 81

Paper consists primarily of cellulose fibers with no specific orientation molded into a sheet. It is well known that paper loses most of its mechanical strength when it is wet with water. The loss of strength does not take place when the paper is wet with oil. Propose an explanation for this observation.

Jennifer Hudspeth

Jennifer Hudspeth

Numerade Educator