Biochemistry Exam 3: Chapter 7 Questions

How many nonreducing ends are possible for a disaccharide?

1 or 2

In a highly ordered theoretical polysaccharide, how many nonreducing ends would be present in a polymer consisting of 155 glucose molecules where branching occurs every five glucose residues?

16

How many chiral centers does D-ribose have?

3

How many epimers of D-glucose exist in its linear form?

3

What is the maximum possible number of stereoisomers in the set that includes the structure shown?

8

What is the structural difference between amylose and amylopectin?

Amylopectin has (α1→6) branch points; amylose only has (α1→4) linkages.

Which statement is true regarding glycogen and amylopectin?

Both are branched polymers of glucose, but glycogen is more extensively branched.

How is chitin different from cellulose?

Chitin has acetylated amino groups on C-2 of the glucose units, cellulose does not.

Why is it NOT a good idea to eat cotton?

Humans lack the enzyme that degrades (β1→4) linkages.

Which repeating disaccharide unit is mismatched with its polymer name?

Hyaluronan; GalA and Fru

What is the benefit of branching in storage polysaccharides?

It creates more nonreducing ends for rapid conversion of polysaccharides to monosaccharides.

Which statement is true about N-acetylneuraminic acid?

It is a sialic acid that occurs in glycoproteins and glycolipids on animal cell surfaces.

Why is lysozyme a useful reagent to use near the beginning of a bacterial DNA isolation protocol?

Lysozyme hydrolyzes glycosidic bonds in peptidoglycan, which aids in cell lysis.

What property of cellulose has made it useful to civilizations for millennia?

Several straight, extended chains laying side by side allows hydroxyl groups to form interchain and intrachain hydrogen bonds.

Which statement is true about natural monosaccharides?

The D-enantiomers predominate.

Consider the linear structures of an aldotetrose and a ketotetrose. Which statement is true?

The aldotetrose has more possible stereoisomers.

Monitoring HbA1c is important for diabetic patients. What does HbA1c measure?

The percent of glycated hemoglobin in the blood.

Which statement is true about glucose in aqueous solution?

There is an equilibrium mixture of the α and β anomers and a trace amount of the linear form.

Why do polysaccharides have indefinite lengths and molecular weights?

There is no specific stopping point in the synthetic process.

How are uronic acids related to the common monosaccharides?

They are monosaccharides that are oxidized to a carboxylate at C-6.

How are glycogen and amylopectin different? a. Structurally they are the same, but glycogen is more compact with more extensive branching. b. Amylopectin has more reducing ends than glycogen. c. The monosaccharide units are joined by different kinds of O-glycosidic bonds. d. Glycogen is a heteropolysaccharide; amylopectin is a homopolysaccharide.

a. Structurally they are the same, but glycogen is more compact with more extensive branching.

Why are the chiral centers found in carbohydrates biologically significant? a. The enzymes that act on sugars are stereospecific. b. Sugar-metabolizing enzymes alter their conformation depending on the stereoisomer being catabolized. c. Solubility depends upon the sugar's stereochemistry. d. Enzymes have to rearrange the stereochemistry on some sugars before metabolizing them.

a. The enzymes that act on sugars are stereospecific.

How do penicillin and related antibiotics work? a. by preventing the synthesis of peptidoglycan cross-links, thereby weakening the bacterial cell wall b. by breaking (β1→4) linkages in the outer coating of viruses c. by interfering with glucose metabolism in bacteria and effectively starving them d. by inhibiting glucose transport proteins in the plasma membrane of bacteria

a. by preventing the synthesis of peptidoglycan cross-links, thereby weakening the bacterial cell wall

α-D-Glucose and α-D-mannose are: a. epimers. b. enantiomers. c. polymers. d. anomers.

a. epimers.

Which glucose polymer(s) can be found in starch?

amylose and amylopectin

What role does chiral chemistry play in the binding of aspartame to the TAS1R2 and TAS1R3 proteins? a. (R,S)-Aspartame binds to the TAS1R2 protein to produce a sweet sensation, whereas (S,S)-aspartame binds to the TAS1R3 protein to produce a bitter sensation. b. (S,S)-Aspartame binds to the TAS1R2 protein to produce a sweet sensation, whereas (R,S)-aspartame binds to a different receptor to produce a bitter sensation. c. (R,S)-Aspartame binds to the TAS1R2 protein to produce a sweet sensation, whereas (S,S)-aspartame does not orient correctly, producing a bitter sensation. d. (S,S)-Aspartame binds to the TAS1R3 protein to produce a sweet sensation, whereas (R,S)-aspartame binds to the TAS1R2 protein to produce a bitter sensation. e. (S,S)-Aspartame binds to the TAS1R2 protein to produce a sweet sensation, whereas (R,S)-aspartame binds to the TAS1R3 protein to produce a bitter sensation.

b. (S,S)-Aspartame binds to the TAS1R2 protein to produce a sweet sensation, whereas (R,S)-aspartame binds to a different receptor to produce a bitter sensation.

Which statement is false regarding the interaction between a ketone and alcohol? a. Anomers are isomers with a configuration difference only in the hemiketal position. b. The reaction between a ketone and sugar molecule forms a glycosidic bond. c. The reaction between the ketone and one alcohol forms a hemiketal. d. The reaction between a hemiketal and one alcohol forms a ketal.

b. The reaction between a ketone and sugar molecule forms a glycosidic bond.

Which polysaccharide segment is shown? SEE PIC a. cellulose b. amylose c. amylopectin d. chitin

b. amylose

What is the difference between D-glucose, D-galactose, and D-mannose? a. the location of the carbonyl group b. the positions of the hydroxyl group on C-2 and/or C-4 c. the number of carbons in the chain d. the stereochemistry on the reference carbon e. the number of hydroxyl groups

b. the positions of the hydroxyl group on C-2 and/or C-4

Dextrans are:

bacterial polysaccharides present in high amount in extracellular adhesives, such as dental plaque.

The difference between glycogen and amylopectin is:

branching frequency

How many reducing ends are present in a molecule of glycogen? a. 2 b. none; glycogen is a nonreducing polysaccharide c. 1 d. n+1, where n equals the number of branches

c. 1

What is the main structural difference between cellulose and amylose? a. The monomer of amylose is glucose; the monomer of cellulose is fructose. b. Amylose is branched; cellulose is not branched. c. Amylose has (α1→4) linkages; cellulose has (β1→4) linkages. d. Amylose has a definite molecular weight; cellulose chains vary in molecular weight.

c. Amylose has (α1→4) linkages; cellulose has (β1→4) linkages.

What must occur for a polysaccharide to be branched? a. A phosphodiester link must join polysaccharide chains at a branch point. b. It must be a heteropolysaccharide. c. At least one monosaccharide unit must be simultaneously bonded to three other monosaccharide units by glycosidic bonds. d. The polysaccharide must contain both O-glycosidic and N-glycosidic bonds.

c. At least one monosaccharide unit must be simultaneously bonded to three other monosaccharide units by glycosidic bonds.

Which statement is false regarding cellulose? a. It is a linear, unbranched homopolysaccharide. b. The glycosidic bonds are (β1→4) linkages. c. It has an acetylated amino group at C-2. d. It contains 10,000 to 15,000 D-glucose units. e. It is a tough, fibrous, water-insoluble substance

c. It has an acetylated amino group at C-2.

Which statement is false regarding chitin? a. It is a linear, unbranched homopolysaccharide. b. It is more hydrophobic and water resistant than cellulose. c. The glycosidic bonds are (α1→4) linkages. d. It is undigestible by vertebrates. e. It has an acetylated amino group at C-2.

c. The glycosidic bonds are (α1→4) linkages.

Which statement is false regarding disaccharides? a. Although there are two monosaccharides involved, there is only one anomeric carbon. b. The disaccharide β-D-galactopyranosyl-(1→4)-β-D-glucopyranose provides sweetness to milk. c. The terminal —CH2OH group is called the reducing end. d. They consist of two monosaccharides joined by an O-glycosidic bond. e. Both anomeric carbons participate in the glycosidic bond to form sucrose.

c. The terminal —CH2OH group is called the reducing end.

Why do many paper towels (which contain high levels of cellulose) often fall apart when wet with water? a. Water protonates the —OH groups on cellulose causing them to repel. b. Water disrupts the hydrophobic interactions holding the cellulose particles together. c. Water competes for the hydrogen bonding between cellulose molecules. d. Water slowly dissolves the cellulose, making a colloidal suspension.

c. Water competes for the hydrogen bonding between cellulose molecules

Polysaccharides: a. must be homopolysaccharides. b. are never branched. c. are glycans. d. have a fixed length.

c. are glycans

What is another word for polysaccharide? a. glyceroside b. glycosylate c. glycan d. glycoside

c. glycan

What feature in the Haworth perspective indicates that a sugar is in the α conformation? a. all hydroxyls pointing down b. the anomeric hydroxyl points up c. the anomeric hydroxyl directionally positioned opposite C-6 d. the terminal —CH2OH group projects upward

c. the anomeric hydroxyl directionally positioned opposite C-6

A major constituent of cotton and linen fabrics is:

cellulose

Glycine and alanine form two possible dipeptides: Gly-Ala and Ala-Gly. How many possible disaccharides can be formed from two molecules of α-D-glucopyranose, using O-glycosidic bonds? a. 1 b. 2 c. 4 d. 5

d. 5

What is the main benefit of storing glucose in a cell as a polysaccharide (e.g., glycogen) instead of as free glucose? a. the polysaccharide has more charged groups, making it more soluble. b. The polysaccharide takes up less physical space. c. The polysaccharide is less susceptible to undesired oxidation. d. Compared to the same number of free glucose molecules, a polysaccharide has far less effect on osmolarity.

d. Compared to the same number of free glucose molecules, a polysaccharide has far less effect on osmolarity.

Which statement is false regarding bacterial cell walls? a. The peptidoglycan wall prevents cellular swelling and lysis due to the osmotic entry of water. b. Short peptides form cross-links between the linear polymers of peptidoglycan. c. Peptidoglycan consists of N-acetylglucosamine and N-acetylmuramic acid residues. d. Peptidoglycan is a homopolymer chain with (α1→4) linkages.

d. Peptidoglycan is a homopolymer chain with (α1→4) linkages.

In a proper Fischer projection, how do you recognize the D form of a monosaccharide aldose? (Note: The first carbon is highest.) a. The —OH group on the second carbon from the top points to the right. b. All of the —OH groups on all of the chiral centers point to the right. c. The carbonyl group on the first carbon points to the right. d. The —OH group on the next to the last carbon atom points to the right.

d. The —OH group on the next to the last carbon atom points to the right.

Which characteristic is NOT true of glycosaminoglycans? a. They contain disaccharide repeat units. b. They are heteropolysaccharides. c. They are found in the extracellular matrix. d. They always contain sulfates.

d. They always contain sulfates.

Which describes the water solubility of monosaccharides? a. They are sparingly soluble due to their primarily hydrophobic organic character. b. Trioses and tetroses are soluble, but the pentoses and larger monosaccharides are insoluble. c. Monosaccharides are soluble only when coupled to a soluble protein. d. They are highly soluble and easily hydrogen-bond with water.

d. They are highly soluble and easily hydrogen-bond with water.

Which statement is NOT a biological role for carbohydrates? a. Their oxidation releases energy. b. They preserve the osmolarity of the cell. c. They are important in the connective tissue of animals, cell recognition, and adhesion. d. They are the building blocks for proteins. e. They provide recognition sites for cells and proteins.

d. They are the building blocks for proteins.

What role does hydrogen bonding play in the structure of starch and glycogen? a. They stabilize straight, unbranched segments held together in layers. b. They hold I3− and I5− iodide molecules tight to the helix core in qualitative tests. c. They form the (β1→4)-linked chains between monomer subunits. d. They stabilize the tightly coiled helix. e. They form the (α1→4)-linked chains between monomer subunits.

d. They stabilize the tightly coiled helix.

What type of monosaccharide is depicted? SEE PIC a. ketopentose because the carbonyl is on an end carbon and there are five hydroxyl groups b. ketohexose because the carbonyl is on an end carbon and there are six carbons c. aldopentose because the carbonyl is on an end carbon and there are five hydroxyl groups d. aldohexose because the carbonyl is on an end carbon and there are six carbons

d. aldohexose because the carbonyl is on an end carbon and there are six carbons

Dextrans are: a. the main glucose-storing polysaccharides in liver tissue. b. heteropolysaccharides involved in plant carbohydrate degradation. c. glucose homopolysaccharides joined by (α1→4) links. d. bacterial polysaccharides present in high amount in extracellular adhesives, such as dental plaque

d. bacterial polysaccharides present in high amount in extracellular adhesives, such as dental plaque

Compare the linear structures of D-glucose and L-glucose. These two molecules have different configurations about _____ carbon atom(s). a. one b. two c. three d. four

d. four

Which heteropolysaccharides are often found in the extracellular matrix (ECM)? a. glycosphingolipids b. fibrillar collagens c. lignin d. glycosaminoglycans

d. glycosaminoglycans

Which is NOT a homopolysaccharide? a. chitin b. cellulose c. dextran d. heparin e. glycogen

d. heparin

Which polysaccharide would have the greatest number of reducing ends? a. cellulose b. glycogen c. amylose d. amylopectin e. Cellulose, glycogen, amylose, and amylopectin all have the same number of reducing ends.

e. Cellulose, glycogen, amylose, and amylopectin all have the same number of reducing ends.

When glucose cyclizes, what organic functional group is generated?

hemiacetal

Which describes the general structure of the rigid component of bacterial cell walls?

heteropolysaccharide chains cross-linked by short amino acid chains

What happens to the number of chiral centers when a monosaccharide cyclizes?

increases by 1

A monosaccharide with a ketone functional group and seven carbons:

is a ketoheptose.

In the synthesis and metabolism of carbohydrates, the intermediates are very often:

phosphorylated sugar derivatives.

A major function of the polysaccharide hyaluronan is that it:

serves as a lubricant in the synovial fluid of joints.

What common disaccharide is Glc(α1↔2β)Fru?

sucrose

What is the systematic name of the disaccharide lactose (β form)?

β-D-galactopyranosyl-(1→4)-β-D-glucopyranose