Chapter 7- Carbohydrates

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

Compare the linear structures of D-glucose and L-glucose. These two molecules have different configurations about _____ carbon atom(s).

4

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?

5

How many stereoisomers does D-ribose, an aldopentose, have?

8 --> The aldopentoses have three chiral centers; therefore, eight (2^3) different stereoisomers are possible

What is the structural difference between amylose and amylopectin?

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

What role do oligosaccharides play in the recognition events of bacterial toxins like cholera at the cell surface?

Binding to cell surface glycolipids before entering the cell.

What effect does lectin have on the blood levels of luteinizing hormone and thyrotropin?

Blood levels undergo a periodic rise and fall due to pulsatile pituitary secretion and constant hepatocyte destruction, respectively.

Which statement is true regarding glycogen and amylopectin? -Glycogen is a form of energy storage in plants, whereas starch is an energy storage form in animals. -Both are polymers of (α1→6)-linked subunits of glucose with (β1→4)-linked branches. -Both are branched polymers of glucose, but glycogen is more extensively branched. -Amylopectin is more compact than glycogen.

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

Which polysaccharide would have the greatest number of reducing ends?

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

How is chitin different from cellulose?

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

What is the main benefit of storing glucose in a cell as a polysaccharide (e.g., glycogen) instead of as free glucose?

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

Which statement is false regarding the structure of monosaccharides? -Cyclization of a ketohexose forms a pyranose. -The orientation of the hydroxyl attack on the carbonyl during the cyclization process determines the α or β configuration. -The chiral carbon farthest from the carbonyl determines the D, L stereochemistry of the carbohydrate. -Cyclization creates one additional chiral carbon.

Cyclization of a ketohexose forms a pyranose.

Which statement is false regarding fibronectin? -Integrins bind to fibronectin to mediate signaling between the cell's interior and the network of molecules in the extracellular matrix. -Integrins bind to the fibronectin conserved AGD sequence (Ala-Gly-Asp). -Fibronectin cross-links with aggrecan to provide strength and resilience to the extracellular matrix. -Separate domains on fibronectin bind fibrin, heparan sulfate, and collagen.

Integrins bind to the fibronectin conserved AGD sequence (Ala-Gly-Asp).

What distinguishes proteoglycans from glycoproteins?

Proteoglycans contain glycosaminoglycans; glycoproteins contain oligosaccharides.

How can a biochemist determine whether or not the monosaccharide sequence is correct?

Synthesize the oligonucleotide and test whether it has the same function as the original.

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

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

Which statement is false regarding the interaction between an aldehyde and alcohol? -The reaction between an aldehyde and sugar molecule forms a glycosidic bond. -The reaction between the aldehyde and one alcohol forms a hemiacetal. -Anomers are isomers with a configuration difference only in the hemiacetal position. -The reaction between a hemiacetal and one alcohol forms an acetal.

The reaction between an aldehyde and sugar molecule forms a glycosidic bond.

How does exhaustive methylation followed by acid hydrolysis aid glycosidic bond position determinations?

The resulting monosaccharides only have free hydroxyl groups where the glycosidic bond existed.

Why do polysaccharides have indefinite lengths and molecular weights?

There is no specific stopping point in the synthetic process.

What is the biological role of oligosaccharides attached to proteins?

They act as destination labels for newly synthesized proteins and also target misfolded proteins for degradation.

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

They always contain sulfates.

Which oligosaccharide characteristic is NOT one of the factors that make analysis complicated?

They bind to proteins or lipids within cells or on the cell surface.

Which statement is false regarding ceruloplasmin? -This is a copper-containing lectin. -Sialic acid protects ceruloplasmin from hepatic degradation. -Endocytosis and destruction result when ceruloplasmin interacts with asialoglycoprotein receptors. -The mechanism that removes sialic acid residues from ceruloplasmin is unclear.

This is a copper-containing lectin.

How might a researcher determine the overall monosaccharide composition of an oligosaccharide?

acid hydrolysis followed by high-performance liquid chromatography

Polysaccharides:

are glycans

Dextrans are:

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

What information do cells encode in oligosaccharides?

cell differentiation and tissue development, intracellular targeting of proteins, cell-cell interactions, and extracellular signals

Which type of bond joins together two monosaccharides?

covalent, glycosidic

How are the positions of the glycosidic bonds determined for amylose?

exhaustive methylation

A furanose ring can be described as a _____-membered ring containing _____.

five; oxygen

What eukaryotic cellular component has a polar head group that forms the outer surface of membranes and an oligosaccharide portion that contains a sialic acid and other monosaccharide residues?

gangliosides

Which macromolecule contains one or more oligosaccharides covalently joined to a protein?

glycoproteins

Which heteropolysaccharides are often found in the extracellular matrix (ECM)?

glycosaminoglycans

Which macromolecule is NOT a glycoconjugate?

glycosaminoglycans

Which macromolecule contains complex oligosaccharide components that act as lectin recognition sites?

glycosphingolipids

Which proteoglycan attaches to the cell membrane by a GPI anchor?

glypicans

When glucose cyclizes, what organic functional group is generated?

hemiacetal

Which proteins "read" the oligosaccharide chains on cells?

lectins

Which cellular component is NOT found in plants or animals? glycolipids proteoglycans glycosphingolipids lipopolysaccharides mucins

lipopolysaccharides

Lectins:

often bind their ligands via multiple weak interactions.

Which molecule contains the sugar code?

oligosaccharide chains

Where are glycolipids and glycoproteins found on the plasma membrane?

on the outer face of the plasma membrane

What type of molecule is integrin?

protein

Protein and nucleic acid sequencing is often less complex than polysaccharide sequencing because:

proteins and nucleic acids are linear polymers, whereas polysaccharides may be branched.

What are lectins?

proteins that bind carbohydrates

Which components comprise the lipid A region of a lipopolysaccharide?

six fatty acid residues and two phosphorylated glucosamines

A carbohydrate chemist synthesizes a glycosaminoglycan to study the biological function of the native compound. What aspect of the newly synthesized structure does the chemist need to verify in order to confirm that it is an exact copy of the native compound?

stereochemistry, chain length, and sulfation pattern

What can be determined by exhaustive methylation of an oligosaccharide with CH3I followed by acid hydrolysis?

the position(s) of glycosidic bonds

How are oligosaccharides released from glycoproteins for analysis?

treatment with either glycosidases or hydrazine

Which feature is consistently observed in glycoproteins?

type of biomolecule attached to the oligosaccharide