100 MCQs on Carbohydrates
Section I: Basics and Classification of Carbohydrates
1. What is the general definition of carbohydrates?
Correct Answer: B. Polyhydroxy aldehydes or ketones, or compounds that yield them on hydrolysis
Explanation: Carbohydrates are broadly defined as polyhydroxy aldehydes or ketones and their derivatives, or compounds that produce such molecules upon hydrolysis.
2. Which three elements are primarily present in carbohydrates?
Correct Answer: B. C, H and O
Explanation: Most carbohydrates contain carbon, hydrogen and oxygen. Many simple carbohydrates approximately follow the empirical formula Cₙ(H₂O)ₙ, although this formula has important exceptions.
3. Which of the following is a monosaccharide?
Correct Answer: C. Glucose
Explanation: Glucose is a monosaccharide, meaning it cannot be hydrolyzed into a simpler carbohydrate.
4. Which of the following is a disaccharide?
Correct Answer: D. Sucrose
Explanation: Sucrose consists of two monosaccharides—glucose and fructose—linked by a glycosidic bond.
5. Which of the following is a polysaccharide?
Correct Answer: C. Glycogen
Explanation: Glycogen is a highly branched polysaccharide composed of numerous glucose units.
6. Carbohydrates containing one sugar unit are called:
Correct Answer: B. Monosaccharides
Explanation: Monosaccharides are the simplest carbohydrates and cannot be hydrolyzed into smaller carbohydrate molecules.
7. Carbohydrates containing two monosaccharide units are called:
Correct Answer: B. Disaccharides
Explanation: Disaccharides consist of two monosaccharide residues connected through a glycosidic linkage.
8. Oligosaccharides generally contain:
Correct Answer: C. A small number of monosaccharide units
Explanation: Oligosaccharides contain a relatively small number of monosaccharide residues, commonly 3–10, although definitions can vary.
9. Polysaccharides are composed of:
Correct Answer: B. A large number of monosaccharide units
Explanation: Polysaccharides are high-molecular-weight carbohydrates consisting of many monosaccharide residues joined by glycosidic bonds.
10. Which of the following is NOT a carbohydrate?
Correct Answer: D. Cholesterol
Explanation: Cholesterol is a sterol/lipid, not a carbohydrate.
Section II: Monosaccharides
11. The simplest aldose is:
Correct Answer: B. Glyceraldehyde
Explanation: Glyceraldehyde is the simplest aldose and contains three carbon atoms.
12. The simplest ketose is:
Correct Answer: B. Dihydroxyacetone
Explanation: Dihydroxyacetone is the simplest ketose and contains three carbon atoms.
13. A monosaccharide containing an aldehyde group is called:
Correct Answer: B. Aldose
Explanation: Aldoses contain an aldehyde functional group, usually at carbon 1 in their open-chain form.
14. A monosaccharide containing a ketone group is called:
Correct Answer: B. Ketose
Explanation: Ketoses contain a ketone functional group, commonly at carbon 2.
15. Glucose is classified as a:
Correct Answer: B. Aldohexose
Explanation: Glucose contains six carbon atoms and an aldehyde group, making it an aldohexose.
16. Fructose is classified as a:
Correct Answer: B. Ketohexose
Explanation: Fructose is a six-carbon sugar containing a ketone group, so it is a ketohexose.
17. Ribose is a:
Correct Answer: A. Aldopentose
Explanation: Ribose has five carbon atoms and an aldehyde group, making it an aldopentose.
18. Ribulose is a:
Correct Answer: B. Ketopentose
Explanation: Ribulose contains five carbon atoms and a ketone group, making it a ketopentose.
19. Galactose is an:
Correct Answer: A. Aldohexose
Explanation: Galactose is a six-carbon aldose and is therefore classified as an aldohexose.
20. Mannose is an:
Correct Answer: A. Aldohexose
Explanation: Mannose is an aldohexose and is closely related stereochemically to glucose.
Section III: Carbon Number and Structure
21. A monosaccharide containing three carbon atoms is called:
Correct Answer: C. Triose
Explanation: Monosaccharides are classified by carbon number: triose = 3, tetrose = 4, pentose = 5, hexose = 6.
22. A four-carbon monosaccharide is called:
Correct Answer: B. Tetrose
Explanation: Tetroses contain four carbon atoms.
23. A five-carbon monosaccharide is called:
Correct Answer: C. Pentose
Explanation: Pentoses contain five carbon atoms. Ribose is an important biological pentose.
24. A six-carbon monosaccharide is called:
Correct Answer: D. Hexose
Explanation: Hexoses contain six carbon atoms. Glucose, fructose, galactose and mannose are examples.
25. How many carbon atoms are present in glucose?
Correct Answer: C. 6
Explanation: Glucose is a hexose, meaning it contains six carbon atoms.
26. How many carbon atoms are present in fructose?
Correct Answer: C. 6
Explanation: Fructose is a ketohexose and therefore contains six carbon atoms.
27. How many carbon atoms are present in ribose?
Correct Answer: C. 5
Explanation: Ribose is a pentose sugar containing five carbon atoms.
28. Which monosaccharide is an important component of RNA?
Correct Answer: B. Ribose
Explanation: RNA contains β-D-ribose as its pentose sugar.
29. Which sugar is present in DNA?
Correct Answer: C. 2-Deoxyribose
Explanation: DNA contains 2-deoxyribose, which lacks the hydroxyl group at the 2′ carbon found in ribose.
30. The molecular formula of glucose is:
Correct Answer: B. C₆H₁₂O₆
Explanation: Glucose has the molecular formula C₆H₁₂O₆.
Section IV: Fischer Projection and D/L Configuration
31. The Fischer projection is commonly used to represent:
Correct Answer: A. Three-dimensional configuration of sugars
Explanation: Fischer projections provide a convenient two-dimensional representation of the stereochemistry of carbohydrates.
32. In a Fischer projection of a monosaccharide, the carbonyl carbon is generally placed:
Correct Answer: B. At the top
Explanation: In the conventional Fischer projection of an aldose, the most oxidized carbon is placed at the top.
33. D/L configuration of a monosaccharide is determined by the configuration of:
Correct Answer: C. The chiral carbon farthest from the carbonyl group
Explanation: In Fischer projections, a sugar is D when the hydroxyl group on the highest-numbered chiral carbon is on the right and L when it is on the left.
34. Most naturally occurring sugars in humans belong predominantly to the:
Correct Answer: B. D-series
Explanation: Many biologically important sugars, including glucose, fructose and galactose, occur predominantly in the D-configuration.
35. D- and L-glucose are:
Correct Answer: C. Enantiomers
Explanation: D- and L-glucose are non-superimposable mirror images and therefore are enantiomers.
36. D- and L-glyceraldehyde are:
Correct Answer: B. Enantiomers
Explanation: D- and L-glyceraldehyde are mirror images and are therefore enantiomers.
37. A carbon atom attached to four different groups is called:
Correct Answer: B. Chiral carbon
Explanation: A carbon attached to four different substituents is generally a chiral/asymmetric carbon center.
38. How many chiral centers are present in open-chain D-glucose?
Correct Answer: C. 4
Explanation: Open-chain glucose has chiral centers at C2, C3, C4 and C5, giving four stereogenic centers.
39. How many stereoisomers are theoretically possible for an aldohexose with four chiral centers?
Correct Answer: C. 16
Explanation: The number of stereoisomers is 2ⁿ, where n is the number of chiral centers. For four centers: 2⁴ = 16.
40. How many stereoisomers are theoretically possible for an aldopentose with three chiral centers?
Correct Answer: C. 8
Explanation: An aldopentose has three chiral centers in its open-chain form. Therefore, 2³ = 8 stereoisomers.
Section V: Anomers and Anomeric Carbon
41. What are anomers?
Correct Answer: B. Sugars differing only at the anomeric carbon
Explanation: Anomers are stereoisomers that differ specifically in configuration at the anomeric carbon.
42. The anomeric carbon of glucose is:
Correct Answer: A. C1
Explanation: Glucose is an aldose. When it cyclizes, its aldehyde carbon, C1, becomes the anomeric carbon.
43. The anomeric carbon of fructose is:
Correct Answer: B. C2
Explanation: Fructose is a ketose. Its ketone carbon at C2 becomes the anomeric carbon during cyclization.
44. In α-D-glucose, the anomeric OH group is:
Correct Answer: B. Trans to the CH₂OH group
Explanation: In the common Haworth representation of D-sugars, the α anomer has the anomeric OH group opposite to the CH₂OH group.
45. In β-D-glucose, the anomeric OH group is:
Correct Answer: B. Cis to CH₂OH
Explanation: In β-D-glucose, the anomeric OH and CH₂OH groups are on the same side in the conventional Haworth projection.
46. α-D-glucose and β-D-glucose are:
Correct Answer: C. Anomers
Explanation: α- and β-D-glucose differ only in configuration at C1, the anomeric carbon, so they are anomers.
47. Which process describes the interconversion of α and β forms of a reducing sugar in solution?
Correct Answer: B. Mutarotation
Explanation: Mutarotation is the change in optical rotation resulting from interconversion between α and β anomers through the open-chain form.
48. Mutarotation occurs because cyclic sugars can:
Correct Answer: B. Open to their linear form and reclose
Explanation: In solution, reducing sugars can transiently open into their linear form and then cyclize again, producing either α or β anomer.
49. Which sugar generally does NOT undergo mutarotation in its glycosidic form?
Correct Answer: C. Sucrose
Explanation: Sucrose has both anomeric carbons involved in its glycosidic linkage. Therefore, neither anomeric center is free to undergo the usual mutarotation process.
50. The cyclic form of glucose is produced by formation of a:
Correct Answer: B. Hemiacetal
Explanation: Intramolecular reaction between the aldehyde group at C1 and the hydroxyl group at C5 produces a cyclic hemiacetal in glucose.
Section VI: Epimers
51. What are epimers?
Correct Answer: B. Sugars differing at one specific chiral center other than the anomeric carbon
Explanation: Epimers are diastereomers that differ in configuration at one, and only one, specific stereogenic center. When that center is the anomeric carbon, the sugars are specifically called anomers.
52. D-glucose and D-galactose are:
Correct Answer: C. Epimers
Explanation: Glucose and galactose differ in configuration only at C4, making them C4 epimers.
53. D-glucose and D-mannose differ at:
Correct Answer: B. C2
Explanation: D-mannose is the C2 epimer of D-glucose.
54. D-glucose and D-galactose differ at:
Correct Answer: C. C4
Explanation: Galactose differs from glucose specifically at carbon 4.
55. Which pair represents C2 epimers?
Correct Answer: B. Glucose and mannose
Explanation: Glucose and mannose differ only at the configuration of C2.
56. Which pair represents C4 epimers?
Correct Answer: B. Glucose and galactose
Explanation: D-glucose and D-galactose are C4 epimers.
57. Anomers are a special type of:
Correct Answer: B. Diastereomers
Explanation: Anomers differ at one stereogenic center and are therefore diastereomers, specifically differing at the anomeric carbon.
58. Epimers are a type of:
Correct Answer: A. Diastereomers
Explanation: Epimers are stereoisomers that differ at only one stereocenter, making them a special class of diastereomers.
59. Which statement is correct?
Correct Answer: B. All anomers are epimers in the broad stereochemical sense
Explanation: Anomers differ at one stereogenic center—the anomeric carbon. However, carbohydrate terminology generally treats anomers as a distinct category from epimers because the differing center is specifically anomeric.
60. Which pair is NOT an example of epimers?
Correct Answer: C. α-D-glucose and β-D-glucose
Explanation: α- and β-D-glucose are anomers, because they differ at the anomeric C1 carbon.
Section VII: Important Monosaccharides and Their Structures
61. Which sugar is commonly known as blood sugar?
Correct Answer: B. Glucose
Explanation: Glucose is the principal circulating sugar in human blood and is an important energy source.
62. Which sugar is commonly known as fruit sugar?
Correct Answer: B. Fructose
Explanation: Fructose occurs naturally in many fruits and is often referred to as fruit sugar.
63. Which monosaccharide is a major component of milk sugar?
Correct Answer: B. Galactose
Explanation: Lactose, the principal sugar in milk, consists of galactose + glucose.
64. Which monosaccharide is a component of glycoproteins and glycolipids?
Correct Answer: A. Mannose
Explanation: Mannose is an important monosaccharide in the biosynthesis and structure of many glycoproteins and glycolipids.
65. Which sugar has a ketone functional group in its open-chain form?
Correct Answer: C. Fructose
Explanation: Fructose is a ketose, with its carbonyl group at C2 in the open-chain form.
66. Which of the following is an aldose?
Correct Answer: C. Glucose
Explanation: Glucose contains an aldehyde group in its open-chain structure and is therefore an aldose.
67. Which of the following is a ketose?
Correct Answer: D. Fructose
Explanation: Fructose contains a ketone group and is classified as a ketohexose.
68. The cyclic form of glucose is predominantly:
Correct Answer: B. Pyranose
Explanation: Glucose predominantly exists in solution as a six-membered glucopyranose ring.
69. A five-membered cyclic sugar ring is called:
Correct Answer: B. Furanose
Explanation: A five-membered ring containing one oxygen atom is called a furanose ring.
70. A six-membered cyclic sugar ring is called:
Correct Answer: B. Pyranose
Explanation: Pyranose forms contain a six-membered ring consisting of five carbons and one oxygen.
Section VIII: Disaccharides
71. Sucrose is composed of:
Correct Answer: B. Glucose + fructose
Explanation: Sucrose consists of glucose and fructose joined through their anomeric carbons.
72. Lactose is composed of:
Correct Answer: C. Galactose + glucose
Explanation: Lactose contains β-D-galactose linked to D-glucose.
73. Maltose is composed of:
Correct Answer: A. Glucose + glucose
Explanation: Maltose contains two glucose residues connected by an α(1→4) glycosidic linkage.
74. Cellobiose consists of:
Correct Answer: C. Glucose + glucose
Explanation: Cellobiose contains two glucose molecules linked by a β(1→4) glycosidic bond.
75. Which disaccharide is commonly called milk sugar?
Correct Answer: C. Lactose
Explanation: Lactose is the major carbohydrate found in mammalian milk and is therefore called milk sugar.
76. Which disaccharide is commonly called table sugar?
Correct Answer: C. Sucrose
Explanation: Sucrose is the common dietary sugar obtained from sugarcane and sugar beet.
77. Which disaccharide is called malt sugar?
Correct Answer: B. Maltose
Explanation: Maltose is commonly called malt sugar and consists of two glucose units.
78. Which disaccharide is a reducing sugar?
Correct Answer: B. Lactose
Explanation: Lactose has a free anomeric carbon on its glucose residue, allowing it to act as a reducing sugar.
79. Sucrose is considered a:
Correct Answer: B. Non-reducing sugar
Explanation: In sucrose, the anomeric carbons of both glucose and fructose participate in the glycosidic bond, leaving no free anomeric carbon.
80. The glycosidic linkage in maltose is:
Correct Answer: A. α(1→4)
Explanation: Maltose contains two glucose units joined by an α(1→4) glycosidic bond.
81. The glycosidic linkage in lactose is:
Correct Answer: B. β(1→4)
Explanation: Lactose contains β-D-galactose-(1→4)-D-glucose.
82. Cellobiose contains which linkage?
Correct Answer: B. β(1→4)
Explanation: Cellobiose consists of two glucose units connected by a β(1→4) linkage.
83. Sucrose contains which glycosidic linkage?
Correct Answer: C. α(1→2)β
Explanation: Sucrose contains an α-D-glucopyranosyl-(1→2)-β-D-fructofuranoside linkage, involving both anomeric carbons.
84. Which enzyme hydrolyzes lactose?
Correct Answer: C. Lactase
Explanation: Lactase hydrolyzes lactose into glucose and galactose.
85. Which enzyme hydrolyzes sucrose?
Correct Answer: B. Sucrase
Explanation: Sucrase hydrolyzes sucrose into glucose and fructose.
Section IX: Reducing and Non-Reducing Sugars
86. A reducing sugar must generally possess:
Correct Answer: A. A free anomeric carbon
Explanation: A free anomeric carbon can allow a cyclic sugar to open into a form containing a reactive carbonyl group, enabling reducing activity.
87. Which of the following is a reducing sugar?
Correct Answer: B. Glucose
Explanation: Glucose has a free anomeric carbon and therefore behaves as a reducing sugar.
88. Which of the following is a non-reducing sugar?
Correct Answer: C. Sucrose
Explanation: Sucrose is non-reducing because both anomeric carbons participate in its glycosidic bond.
89. Which test is commonly used to detect reducing sugars?
Correct Answer: B. Benedict's test
Explanation: Benedict's reagent can be reduced by reducing sugars, producing a colored precipitate of copper(I) oxide under suitable conditions.
90. Which of the following is generally NOT a reducing sugar?
Correct Answer: D. Sucrose
Explanation: Sucrose lacks a free anomeric carbon because both anomeric centers are involved in the glycosidic linkage.
Section X: Polysaccharides
91. Starch is primarily a storage polysaccharide in:
Correct Answer: B. Plants
Explanation: Starch is the major storage polysaccharide of plants.
92. Glycogen is primarily a storage polysaccharide in:
Correct Answer: B. Animals
Explanation: Glycogen is the major carbohydrate storage form in animals, especially in liver and skeletal muscle.
93. The major storage polysaccharide in animals is:
Correct Answer: C. Glycogen
Explanation: Animals store glucose mainly as glycogen, a highly branched glucose polymer.
94. The major structural polysaccharide of plant cell walls is:
Correct Answer: B. Cellulose
Explanation: Cellulose is a major structural component of plant cell walls.
95. Cellulose is composed of:
Correct Answer: B. β-D-glucose units
Explanation: Cellulose consists of glucose residues linked by β(1→4) glycosidic bonds.
96. The glycosidic linkage in cellulose is:
Correct Answer: B. β(1→4)
Explanation: β(1→4) linkages produce long, straight cellulose chains capable of extensive hydrogen bonding.
97. Starch consists primarily of:
Correct Answer: B. Amylose and amylopectin
Explanation: Starch has two major components: amylose, which is predominantly linear, and amylopectin, which is branched.
98. Which component of starch is predominantly unbranched?
Correct Answer: A. Amylose
Explanation: Amylose consists mainly of glucose units linked by α(1→4) bonds and is largely unbranched.
99. Which component of starch is branched?
Correct Answer: B. Amylopectin
Explanation: Amylopectin contains α(1→4) linkages in the main chains and α(1→6) linkages at branch points.
100. Which statement correctly compares cellulose and glycogen?
Correct Answer: B. Cellulose is a structural polymer with β(1→4) linkages, whereas glycogen is a highly branched storage polymer with α linkages
Explanation: Cellulose is a structural glucose polymer with β(1→4) linkages, whereas glycogen is a highly branched glucose storage polymer containing α(1→4) chains and α(1→6) branch points.
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