Question 1

(a)Define "reducing sugar." 
(b)Show the reaction product of glucose after it is used as a reducing sugar.
(c)Explain why fructose is also considered a reducing sugar.(Hint: It must first undergo a chemical conversion. )
(d)Sucrose is a disaccharide composed of glucose and fructose
(Glc($\beta$1 $\rightarrow$ 2)Fru).Explain why sucrose is not a reducing sugar,even though both glucose and fructose are.

Accepted Answer

The answer of (a)Define "reducing sugar." 
(b)Show the reaction product...

Question 2

Which of the following statements concerning sialic acid residues on glycoproteins is true?
A)Sialic residues on erythrocytes are recognized by lectins,leading to removal of the erythrocytes.
B)Sialic residues on ceruloplasmin are recognized by lectins,leading to removal of ceruloplasmin.
C)Sialic residues are removed by neuraminidases.
D)The anti-viral drug oseltamavir accelerates the removal of sialic acid residues.
E)Both A and B above

Accepted Answer

Sialic residues are removed by neuraminidases. Lectins do recognize sialic residues on erythrocytes and other cells, but this does not lead to removal of the cells. The anti-viral drug oseltamavir inhibits neuraminidase activity and thus slows down the removal of sialic acid residues. Option A and B are incorrect.

Question 3

The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to:
A)amphipathic molecules.
B)hydrophobic molecules.
C)specific lipids.
D)specific oligosaccharides.
E)specific peptides.

Accepted Answer

Lectins are proteins that have the ability to selectively bind carbohydrates, specifically oligosaccharides. This property allows them to participate in a variety of biological processes, including cell-cell interactions, cell signaling, and pathogen recognition.

Question 4

In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues: 
A)asparagine,serine,or threonine.
B)aspartate or glutamate.
C)glutamine or arginine.
D)glycine,alanine,or aspartate.
E)tryptophan,aspartate,or cysteine.

Accepted Answer

Carbohydrate moieties in glycoproteins are typically attached to the amino acid residues asparagine, serine, or threonine through an N-glycosidic bond. This is the most common type of glycosylation in glycoproteins.

Question 5

Why is it surprising that the side chains of tryptophan residues in lectins can interact with sugars?
A)Because the side chain of tryptophan is hydrophilic and sugars are hydrophobic
B)Because the side chain of tryptophan is (-)charged and sugars are generally (+)charged or neutral
C)Because the side chain of tryptophan can make hydrogen bonds and sugars cannot.
D)Because the side chain of tryptophan is hydrophobic and sugars are generally hydrophilic
E)None of the above

Accepted Answer

The side chain of tryptophan is typically considered hydrophobic, while sugars are generally hydrophilic. This makes it surprising that the side chains of tryptophan residues in lectins interact with sugars.

Question 6

Which of the following is not a reason that it is difficult to study oligosaccharide composition from biological systems?
A)Oligosaccharides are often branched.
B)Oligosaccharides often have a high negative charge density.
C)Oligosaccharides have a variety of linkages .
D)Oligosaccharides have too much conformational flexibility.
E)There are no specific glycosidase enzymes that can be used to selectively digest oligosaccharides.

Accepted Answer

The other options are all reasons why it is difficult to study oligosaccharide composition from biological systems, but not option D. Oligosaccharides have a significant amount of conformational flexibility, which can make it difficult to determine their exact composition and structure.

Question 7

Which of the following statements about heparan sulfate is not true?
A)Sulfation of heparan sulfate to form NS domains is important for its role as an anti-coagulant.
B)Heparan sulfate can promote protein-protein interactions via the NS domains.
C)The secondary structure of heparan sulfate is completely random.
D)The NA domains of heparan sulfate contain no sulfation.
E)The core repeating structure of heparan sulfate is made up of alternating GlcNAc and GlcA.

Accepted Answer

The secondary structure of heparan sulfate is not completely random. It has a specific unbranched structure with alternating sulfated and non-sulfated regions.

Question 8

Define each in 20 words or fewer:
(a)anomeric carbon
(b)enantiomers
(c)furanose
(d)pyranose
(e)glycoside
(f)epimers
(g)aldose
(h)ketose

Accepted Answer

The answer of Define each in 20 words or fewer:
(a)anomeric...

Question 9

The number of structurally different polysaccharides that can be made with 20 different monosaccharides is far greater than the number of different polypeptides that can be made with 20 different amino acids if both polymers contain an equal number (say 100)of total residues.Explain why.

Accepted Answer

The answer of The number of structurally different polysaccharides that...

Question 10

Categorize each of the following as an aldose,a ketose,or neither.

Accepted Answer

The answer of Categorize each of the following as an...

Question 11

Which of the following techniques is not commonly used to study oligosaccharide structures?
A)X-ray crystallography
B)Matrix-assisted laser desorption/ionization mass spectroscopy (MALDI-MS)
C)Nuclear magnetic resonance (NMR)
D)Complete chemical synthesis
E)Oligosaccharide microarrays

Accepted Answer

The answer of Which of the following techniques is not...

Question 12

In the following structure:  (a)How many of the monosaccharide units are furanoses and how may are pyranoses? 
(b)What is the linkage between the two monosaccharide units? 
(c)Is this a reducing sugar?

Accepted Answer

The answer of In the following structure:  (a)How many...

Question 13

This compound is l-glyceraldehyde.Draw a stereochemically correct representation of C-1 and C-2 of d-glucose.

Accepted Answer

The answer of This compound is l-glyceraldehyde.Draw a stereochemically correct...

Question 14

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

Accepted Answer

The answer of Explain why all mono- and disaccharides are...

Question 15

Which of the following is a dominant feature of the outer membrane of the cell wall of gram negative bacteria?
A)Amylose
B)Cellulose
C)Glycoproteins
D)Lipopolysaccharides
E)Lipoproteins

Accepted Answer

Lipopolysaccharides are a major component of the outer membrane of gram negative bacteria and play a key role in the pathogenicity of these organisms. They can trigger a strong immune response in humans, leading to fever, shock and even death.

Question 16

Explain how it is possible that a polysaccharide molecule,such as glycogen,may have only one reducing end,and yet have many nonreducing ends.

Accepted Answer

The answer of Explain how it is possible that a...

Question 17

Describe one biological advantage of storing glucose units in branched polymers (glycogen,amylopectin)rather than in linear polymers.

Accepted Answer

The answer of Describe one biological advantage of storing glucose...

Question 18

(a)Draw the structures of both anomers of glucose in the pyranose ring form.
(b)How many asymmetric carbons (chiral centers)does each of these structures have? 
(c)How many stereoisomers of the glucose are theoretically possible?

Accepted Answer

The answer of (a)Draw the structures of both anomers of...

Question 19

In measuring long-term glucose levels in the bloodstream,glycated hemoglobin must be separated from unmodified hemoglobin to determine the percentage of glycated hemoglobin.Suggest a simple chromatographic method by which this separation can be performed.

Accepted Answer

The answer of In measuring long-term glucose levels in the...

Question 20

Identify all the epimeric pairs in the structures shown below.

Accepted Answer

The answer of Identify all the epimeric pairs in the...

Quiz 7: Carbohydrates and Glycobiology

Which of the following statements concerning sialic acid residues on glycoproteins is true?

The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to:

In glycoproteins, the carbohydrate moiety is always attached through the amino acid residues:

Why is it surprising that the side chains of tryptophan residues in lectins can interact with sugars?

Which of the following is not a reason that it is difficult to study oligosaccharide composition from biological systems?

Which of the following statements about heparan sulfate is not true?

Define each in 20 words or fewer: (a)anomeric carbon (b)enantiomers (c)furanose (d)pyranose (e)glycoside (f)epimers (g)aldose (h)ketose

The number of structurally different polysaccharides that can be made with 20 different monosaccharides is far greater than the number of different polypeptides that can be made with 20 different amino acids if both polymers contain an equal number (say 100)of total residues.Explain why.

Categorize each of the following as an aldose,a ketose,or neither.

Which of the following techniques is not commonly used to study oligosaccharide structures?

In the following structure: (a)How many of the monosaccharide units are furanoses and how may are pyranoses? (b)What is the linkage between the two monosaccharide units? (c)Is this a reducing sugar?