CARBOHYDRATES

1. D-glucose and L-glucose are

a. diasteroisomers.

b. enantiomers.

c. epimers.

2. Complete the statement: The furanose form of fructose is generated by formation of a hemiketal involving the attack of the hydroxyl group on carbon ____ with carbon ____ .

a. 5, 2

b. 2, 6

c. 6, 1

3. Formation of pyranose and furanose forms of sugar result in the generation of a new asymmetric carbon giving rise to α- and β- forms of the sugars. The carbon at which this newly created asymmetric center is generated is referred to as

a. the anomeric carbon.

b. the epimeric carbon.

c. carbon number 1 in the numbering scheme for sugars.

4. The most stable conformation of the pyranose for six-carbon sugars is the

a. planar conformation

b. boat conformation

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c. chair conformation

5. Once formed, the α and β forms of D-glucose are

a. not capable of interconversion.

b. interconvertible directly with no intermediate and are in equilibrium with one another.

c. interconvertible only through a linear, noncyclic intermediate with which they are both in equilibrium.

6. Glycosidic bonds

a. connect sugar molecules in both linear and branches of complex carbohydrates.

b. only connect carbon-1 of one sugar to carbon-4 of another.

c. destroy the asymmetric character of the participating carbons.

7. Human blood groups (ABO) are

a. the result of the same oligosaccharides being attached to different proteins.

b. the result of differing glycotransferases.

c. the result of the presence or absence of certain sugars.

8. Glycoproteins are proteins to which carbohydrates have been covalently attached. The amino acid R groups that serve as the sites for such attachment include

a. negatively charged amino acid R-groups.

b. cysteine.

c. hydroxyl-containing R-groups.

9. The processes of N-linked and O-linked glycosylation

a. both take place in the endoplasmic reticulum.

b. both take place in the Golgi apparatus.

c. both occur while the protein is being synthesized on the ribsosome.

10. Glycoproteins are targeted to different parts of the cell for secretion. This sorting, which targets the glycoproteins to their correct destination, is done in what organelle?

a. the lysozome

b. the endoplasmic reticulum

c. the Golgi apparatus

ANSWERS

1. D-glucose and L-glucose are

a. diasteroisomers.

b. enantiomers.

c. epimers.

1 out of 1Correct. D- and L-glucose are mirror images of one another and thus enatiomers.

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2. Complete the statement: The furanose form of fructose is generated by formation of a hemiketal involving the attack of the hydroxyl group on carbon ____ with carbon ____ .

a. 5, 2

b. 2, 6

c. 6, 1

1 out of 1Correct. This generates the five-member furanose ring typical of fructose.

3. Formation of pyranose and furanose forms of sugar result in the generation of a new asymmetric carbon giving rise to α- and β- forms of the sugars. The carbon at which this newly created asymmetric center is generated is referred to as

a. the anomeric carbon.

b. the epimeric carbon.

c. carbon number 1 in the numbering scheme for sugars.

1 out of 1Correct. The anomeric position is defined as the newly generated asymmetric carbon.

4. The most stable conformation of the pyranose for six-carbon sugars is the

a. planar conformation

b. boat conformation

c. chair conformation

1 out of 1Correct. The chair conformation is the least strained and most stable pyranose structure

5. Once formed, the α and β forms of D-glucose are

a. not capable of interconversion.

b. interconvertible directly with no intermediate and are in equilibrium with one another.

c. interconvertible only through a linear, noncyclic intermediate with which they are both in equilibrium.

1 out of 1Correct. Although present in only a small amount, the linear form of glucose is in equilibrium with both anomers.

6. Glycosidic bonds

a. connect sugar molecules in both linear and branches of complex carbohydrates.

b. only connect carbon-1 of one sugar to carbon-4 of another.

c. destroy the asymmetric character of the participating carbons.

1 out of 1Correct. Glycogen, for example, has both linear and branch glycosidic linkages.

7. Human blood groups (ABO) are

a. the result of the same oligosaccharides being attached to different proteins.

b. the result of differing glycotransferases.

c. the result of the presence or absence of certain sugars.

1 out of 1Correct. The A and B transferases differ in which monosaccharide is added to the O antigen

8. Glycoproteins are proteins to which carbohydrates have been covalently attached. The amino acid R groups that serve as the sites for such attachment include

a. negatively charged amino acid R-groups.

b. cysteine.

c. hydroxyl-containing R-groups.

1 out of 1Correct. The O-linked glycoproteins involve ether linkages between sugars and hydroxyl groups of serine and threonine.

9. The processes of N-linked and O-linked glycosylation

a. both take place in the endoplasmic reticulum.

b. both take place in the Golgi apparatus.

c. both occur while the protein is being synthesized on the ribsosome.

1 out of 1Correct. Although N-linked glycosylation begins in the endoplasmic reticulum, it continues in the Golgi apparatus. O-linked glycosylation occurs exclusively in the Golgi apparatus.

10. Glycoproteins are targeted to different parts of the cell for secretion. This sorting, which targets the glycoproteins to their correct destination, is done in what organelle?

a. the lysozome

b. the endoplasmic reticulum

c. the Golgi apparatus

1 out of 1Correct. In addition to continuing the glycosylation process, the Golgi apparatus is the major site where glycoproteins are sorted and targeted to their final destination.