Chapter 7 Iclicker questions

Even though amylose and cellulose are made of similar homopolysaccharide chains, they have very different properties. Why? A. The β-glycosidic linkage of glucose molecules in cellulose form interchain and intrachain hydrogen bonds that produce straight, stable fibers that exclude water. B. Cellulose is composed of galactose, while amylose is composed of glucose. C. The α-glycosidic linkage of glucose molecules in amylose causes it to form helices that exclude water. D. Amylose makes a linear polymer which cannot make hydrogen bonds.

A. The β-glycosidic linkage of glucose molecules in cellulose form interchain and intrachain hydrogen bonds that produce straight, stable fibers that exclude water. The glucose residues in cellulose are linked by (β1→4) glycosidic bonds, allowing for the formation of interchain and intrachain hydrogen bonds.

Glucose is a monosaccharide with a(n): A. aldehyde functional group and six carbons. B. ketone functional group and six carbons. C. aldehyde functional group and seven carbons. D. ketone functional group and seven carbons.

A. aldehyde functional group and six carbons. Glucose is an aldohexose, a monosaccharide with an aldehyde functional group and six carbons.

Cyclization of monosaccharides: A.is the reaction of hemiketal or hemiacetal formation. B.is irreversible. C. creates α and β epimers. D. only occurs in hexoses.

A. is the reaction of hemiketal or hemiacetal formation. In aqueous solution, all monosaccharides with five or more carbon atoms in the backbone occur predominantly as cyclic (ring) structures in which the carbonyl group has formed a covalent bond with the oxygen of a hydroxyl group in the same sugar molecule. The formation of these ring structures is the result of a general reaction between alcohols and aldehydes or ketones to form derivatives called hemiacetals or hemiketals.

What term is given to carbohydrates linked by their anomeric carbons? A. nonreducing sugars B. glycosides C. anomers D. hemiketals

A. nonreducing sugars When the anomeric carbon is involved in a glycosidic bond, the easy interconversion of linear and cyclic forms is prevented. Formation of a glycosidic bond therefore renders a sugar nonreducing.

Lectins: A. often bind their ligands via multiple weak interactions. B. bind their ligands with relatively low specificity. C. prevent viruses from binding to their target cells. D. are carbohydrates that bind to receptor proteins.

A. often bind their ligands via multiple weak interactions. Many sugars have a more polar side and a less polar side; the more polar side hydrogen-bonds with the lectin, while the less polar side undergoes interactions with nonpolar amino acid residues through the hydrophobic effect. The sum of all these interactions produces high-affinity binding and high specificity of lectins for their carbohydrate ligands.

Which of these is NOT a glycoconjugate? A. trehalose B. syndecan C. glypican D. glycosphingolipid

A. trehalose A glycoconjugate is a biologically active molecule in which an informational carbohydrate is covalently joined to a protein or a lipid. Trehalose is a disaccharide of glucose.

Which of these sugars is nonreducing? A. trehalose B. glucose C. maltose D. lactose

A. trehalose When the anomeric carbon is involved in a glycosidic bond, the easy interconversion of linear and cyclic forms is prevented. Formation of a glycosidic bond therefore renders a sugar nonreducing. Trehalose is a disaccharide of D-glucose that is a nonreducing sugar

Why are chitin and cellulose hydrophobic and essentially insoluble in an aqueous media? A. Because polymers of these molecules pack so tightly together, there is no geometric space left for water. B. Because they form many internal hydrogen bonds, they leave no sites for binding to water. C. Because there are no enzymes that can break the beta linkages. D. Because the linear polymer cannot make hydrogen bonds.

B. Because they form many internal hydrogen bonds, they leave no sites for binding to water. The residues in chitin and cellulose are both linked by (β1→4) linkages, allowing for the formation of internal hydrogen bonds.

Which statement about glycoconjugates is false? A. The glycosaminoglycan chain of the proteoglycan can bind to extracellular proteins through electrostatic interactions. B. Glycolipids are found in specific organelles, such as Golgi complexes. C. Glycosphingolipids play a role in signal transduction. D. The oligosaccharide portions of glycoproteins are very heterogeneous.

B. Glycolipids are found in specific organelles, such as Golgi complexes. Inside cells, glycoproteins are found in specific organelles such as Golgi complexes (where the oligosaccharide moieties are added to the proteins), secretory granules, and lysosomes. Glycolipids are plasma membrane components in which the hydrophilic head groups are oligosaccharides.

A laboratory is studying the binding properties of a glycoprotein on the plasma membrane. What amino acids should they analyze for the presence of branched heteropolysaccharides? A. Ser, Thr, and Tyr B. Ser, Thr, and Asn C. Trp, Tyr, and Phe D. Lys, His, and Arg

B. Ser, Thr, and Asn Glycoproteins are carbohydrate-protein conjugates. The carbohydrate is attached at its anomeric carbon through a glycosidic link to the —OH of a Ser or Thr residue (O-linked), or through an N-glycosyl link to the amide nitrogen of an Asn residue (N-linked).

Using the Fischer projection of D-glucose, identify which statement is true of the Haworth perspective formula of α-D-glucopyranose. A. The terminal —CH2OH group projects downward. B. The anomeric hydroxyl is on the opposite side from C-6. C. The hydroxyl group on C-2 is placed pointing up. D. The cyclic structure is a five-membered ring.

B. The anomeric hydroxyl is on the opposite side from C-6. For an α structure, the anomeric carbon (C-1) has its hydroxyl group placed on the opposite side from C-6.

Which characteristic is NOT one that is true of glycosaminoglycans? A. found in extracellular matrix B. always contain sulfates C. are heteropolysaccharides D. are disaccharide repeat units

B. always contain sulfates The glycosaminoglycans, are a family of linear polymers composed of repeating disaccharide units. Some, but not all, glycosaminoglycans contain esterified sulfate groups.

The ________ does NOT need to be determined in fully characterizing oligosaccharides and polysaccharides. A. sequence of monosaccharides B. amino acid sequence of the protein C. location of branch points D. α-versus-β configurations of linkages

B. amino acid sequence of the protein Oligosaccharides and polysaccharides are sugar polymers containing multiple monosaccharide units. Determination of the amino acid sequence is only needed if the oligosaccharide of polysaccharide is conjugated to a protein.

Polysaccharides: A. do not fold into three-dimensional structures. B. are glycans. C. must be homopolysaccharides. D. are never branched.

B. are glycans. Polysaccharides are also called glycans.

Glycoproteins: A. contain unbranched oligosaccharides. B. are sometimes intracellular. C. have oligosaccharides covalently attached to aspartate residues. D. are a small fraction of the total number of proteins in a human cell.

B. are sometimes intracellular. Many of the proteins secreted by eukaryotic cells are glycoproteins, including most of the proteins of blood. Some of the proteins secreted by the pancreas are glycosylated, as are most of the proteins contained in lysosomes.

The glycosaminoglycan hyaluronan: A.is a homopolysaccharide. B.consists of alternating residues of D-glucuronic acid and N-acetylglucosamine. C.is covalently linked to specific proteins. D.is a much shorter polymer than heparin.

B. consists of alternating residues of D-glucuronic acid and N-acetylglucosamine. The glycosaminoglycan hyaluronan (hyaluronic acid) contains alternating residues of D-glucuronic acid and N-acetylglucosamine.

A monosaccharide with a ketone functional group and seven carbons: A.can never exist in cyclic form. B.is a ketoheptose. C.is the monosaccharide found in RNA but not DNA. D.has a single chiral center.

B. is a ketoheptose. Monosaccharides with seven carbon atoms in their backbones are called heptoses. A ketose of this chain length is a ketoheptose.

What chemical feature determines if a sugar is an aldose or a ketose? A.the direction of rotation of polarized light B.the position of the carbonyl carbon C.if the enantiomers resemble either glyceraldehyde or dihydroxyacetone D.if the epimers differ in configuration around one carbon or more than one carbon

B. the position of the carbonyl carbon The backbones of common monosaccharides are unbranched carbon chains in which all the carbon atoms are linked by single bonds. In this open-chain form, one of the carbon atoms is double-bonded to an oxygen atom to form a carbonyl group. If the carbonyl group is at an end of the carbon chain, the monosaccharide is an aldose. If the carbonyl group is at any other position, it is a ketose.

A glycogen molecule with 28 branches has how many nonreducing and reducing ends? A.28 nonreducing ends and 28 reducing ends B.29 nonreducing ends and 1 reducing end C.1 nonreducing end and 29 reducing ends D.1 nonreducing end and 1 reducing end

B.29 nonreducing ends and 1 reducing end Because each branch of glycogen ends with a nonreducing sugar unit, a glycogen molecule with n branches has n + 1 nonreducing ends, but only one reducing end. Thus, a glycogen molecule with 28 branches has 29 nonreducing ends and 1 reducing end.

Why does (R,S)-aspartame NOT stimulate the sweet receptor? A. Site AH+ cannot bind the partially negative oxygen of the carboxylic acid. B. Site B- cannot hydrogen bond with the amine nitrogen. C. Site X cannot accommodate the hydrophobic benzene ring. D. None of the sites can interact with (R,S)-aspartame.

C. Site X cannot accommodate the hydrophobic benzene ring. The steric match must be correct to stimulate the sweet receptor. Site X is oriented perpendicular to AH+ and B- and can accommodate the hydrophobic benzene ring of (S,S)-aspartame. However, Site X cannot accommodate the hydrophobic benzene ring of (R,S)-aspartame.

Which statement about proteoglycans is false? A. They contain protein. B. They can affect ligand-receptor interactions. C. They are always extracellular. D. They contain glycosaminoglycans.

C. They are always extracellular. Proteoglycans are macromolecules of the cell surface or ECM in which one or more sulfated glycosaminoglycan chains are joined covalently to a membrane protein or a secreted protein.

A(n) ________ is a(n) ________ with two monosaccharide units. A.oligosaccharide; polysaccharide B.polysaccharide; oligosaccharide C.disaccharide; oligosaccharide D.disaccharide; polysaccharide

C. disaccharide; oligosaccharide Oligosaccharides consist of short chains of monosaccharide units, or residues, joined by characteristic linkages called glycosidic bonds. The most abundant are the disaccharides, with two monosaccharide units.

Oligosaccharides are: A. never found in mucins. B. classified as a N- or O-linked when found in gangliosides. C. found in bacterial lipopolysaccharides. D. never attached to hormones.

C. found in bacterial lipopolysaccharides. The lipopolysaccharides of S. typhimurium contain six fatty acids bound to two glucosamine residues, one of which is the point of attachment for a complex oligosaccharide. E. coli has similar but unique lipopolysaccharides.

Which item is NOT associated with disaccharides? A. O-glycosidic linkages B. formation of a ketal or acetal C. never having free anomeric carbons D. sucrose

C. never having free anomeric carbons In describing disaccharides and polysaccharides, the end of a chain with a free anomeric carbon (one not involved in a glycosidic bond) is called the reducing end. There are a number of disaccharides with free anomeric carbons, including glucose and lactose.

Following the convention for naming reducing oligosaccharides, what is the name of lactose, as shown. A. α-L-glucopyranose-(1→6)-α-L-galactopyranosyl B. β-D-glucopyranose-(1→4)-β-D-galactopyranosyl C. β-D-galactopyranosyl-(1→4)-β-D-glucopyranose D. α-L-galactopyranosyl-(1→6)-α-L-glucopyranose

C. β-D-galactopyranosyl-(1→4)-β-D-glucopyranose The image is drawn with the nonreducing end on the left. The anomeric carbon joining the first unit to the second is β and the nonreducing unit is the six-membered ring D-galactose. A (1→4)-glycosidic bond links the two monosaccharides together. The second residue is the six-membered ring D-glucose.

Which statement is false regarding homopolysaccharides and heteropolysaccharides? A.Homopolysaccharides contain a single monomeric sugar species. B.Some homopolysaccharides serve as structural elements in animal exoskeletons. C.Heteropolysaccharides serve as storage forms of monosaccharides that are used as fuel. D.In animal tissues, the extracellular space is occupied by several types of heteropolysaccharides.

C.Heteropolysaccharides serve as storage forms of monosaccharides that are used as fuel. Some homopolysaccharides serve as storage forms of monosaccharides that are used as fuels; starch and glycogen are homopolysaccharides of this type

What O-glycosidic bond is commonly found in amylose, amylopectin, and glycogen? A.(β1"4) B.(α1"6) C.(β1"6) D.(α1"4)

D. (α1"4) Amylose, amylopectin, and glycogen all contain (α1→4) linkages joining successive glucose residues.

Which statement is false regarding the enantiomers of glyceraldehyde? A. The enantiomers of glyceraldehyde are mirror images of each other. B. Because glyceraldehyde contains one chiral center, it has two enantiomers. C. In the Fischer projection formula for D-glyceraldehyde, the hydroxyl group is on the right. D. Glyceraldehyde does not occur in optically active isomeric forms.

D. Glyceraldehyde does not occur in optically active isomeric forms. All the monosaccharides except dihydroxyacetone contain one or more asymmetric (chiral) carbon atoms and thus occur in optically active isomeric forms. The simplest aldose, glyceraldehyde, contains one chiral center (the middle carbon atom) and therefore has two different optical isomers, or enantiomers.

Which statement about selectins is false? A. They mediate cell-cell recognition. B. They are involved in the movement of immune system cells. C. They can be involved in the process rejection of transplanted organs. D. They are intracellular.

D. They are intracellular. Selectins are a family of plasma membrane lectins that mediate cell-cell recognition and adhesion in a wide range of cellular processes.

What name is given to monosaccharides that differ in configuration about the hemiacetal carbon atom? A. enantiomers B. isomers C. epimers D. anomers

D. anomers Isomeric forms of monosaccharides that differ only in their configuration about the hemiacetal or hemiketal carbon atom are called anomers.

Which reaction is one that is NOT common of glucose? A .mutarotation B. oxidation to an aldonic acid C .oxidation to an uronic acid D. oxidation by reducing sugars

D. oxidation by reducing sugars Glucose does not undergo oxidation by reducing sugars. Glucose itself is a reducing sugar. Free aldehyde groups in glucose undergo a characteristic redox reaction with Cu2+ under alkaline conditions. As glucose is oxidized from aldehyde to carboxylic acid, Cu2+ is reduced to Cu+, which forms a brick-red precipitate

Why is it logical for sugars to be added to only one end of glycogen, making them excellent molecules for glucose storage? A. Because the other end of the molecule is anchored to a membrane with a lipid. B. Because it is the reducing end, and a reduction reaction is the mechanism for adding the sugar. C. Because it has the hemiacetal carbon, the one carbon to which more sugars can be attached. D. Because there are many nonreducing ends on one molecule, allowing rapid glucose storage and release.

D.Because there are many nonreducing ends on one molecule, allowing rapid glucose storage and release. A glycogen molecule with n branches has n + 1 nonreducing ends. When glycogen is used as an energy source, glucose units are removed one at a time from the nonreducing ends. Degradative enzymes that act only at nonreducing ends can work simultaneously on the many branches, speeding the conversion of the polymer to monosaccharides.