1. What is the general empirical chemical formula for most simple carbohydrates (monosaccharides)?
Correct Answer: A ((CH2O)n)
Monosaccharides typically follow the empirical formula (CH2O)n, representing “hydrates of carbon.”
Monosaccharides typically follow the empirical formula (CH2O)n, representing “hydrates of carbon.”
2. Which functional group is present in an aldose sugar?
Correct Answer: A (Aldehyde group (-CHO))
Aldoses are monosaccharides containing an aldehyde group on the terminal carbon (C1), such as glucose and galactose.
Aldoses are monosaccharides containing an aldehyde group on the terminal carbon (C1), such as glucose and galactose.
3. Which of the following is an example of a ketohexose sugar?
Correct Answer: C (Fructose)
Fructose has 6 carbon atoms (hexose) with a ketone group at carbon 2, making it a ketohexose.
Fructose has 6 carbon atoms (hexose) with a ketone group at carbon 2, making it a ketohexose.
4. What is the simplest ketotriose monosaccharide that lacks a chiral center?
Correct Answer: B (Dihydroxyacetone)
Dihydroxyacetone is the only naturally occurring monosaccharide that does not have an asymmetric (chiral) carbon atom.
Dihydroxyacetone is the only naturally occurring monosaccharide that does not have an asymmetric (chiral) carbon atom.
5. What covalent bond links two monosaccharide units together?
Correct Answer: C (Glycosidic bond)
A glycosidic bond forms through a condensation reaction between the anomeric hydroxyl of a sugar and a functional group of another molecule.
A glycosidic bond forms through a condensation reaction between the anomeric hydroxyl of a sugar and a functional group of another molecule.
6. Table sugar (Sucrose) is a disaccharide composed of which two monosaccharides?
Correct Answer: A (Glucose + Fructose)
Sucrose is formed by an alpha-D-glucopyranosyl-(1→2)-beta-D-fructofuranoside glycosidic linkage.
Sucrose is formed by an alpha-D-glucopyranosyl-(1→2)-beta-D-fructofuranoside glycosidic linkage.
7. Why is sucrose classified as a non-reducing sugar?
Correct Answer: B (Both anomeric carbons are involved in the glycosidic bond)
The linkage between C1 of glucose and C2 of fructose ties up both reducing ends, leaving no free anomeric carbon to open into a reactive aldehyde or ketone.
The linkage between C1 of glucose and C2 of fructose ties up both reducing ends, leaving no free anomeric carbon to open into a reactive aldehyde or ketone.
8. Lactose (milk sugar) consists of which two monosaccharides joined by a beta-(1→4) glycosidic bond?
Correct Answer: B (Galactose + Glucose)
Lactose is a reducing disaccharide synthesized from beta-D-galactose and D-glucose.
Lactose is a reducing disaccharide synthesized from beta-D-galactose and D-glucose.
9. Maltose is produced by the enzymatic hydrolysis of starch and consists of:
Correct Answer: A (Two Glucose units joined by an alpha-(1→4) bond)
Maltose is a disaccharide made of two D-glucose molecules linked via an alpha-(1→4) glycosidic bond.
Maltose is a disaccharide made of two D-glucose molecules linked via an alpha-(1→4) glycosidic bond.
10. Two sugars that differ in configuration only around a single specific carbon atom (e.g., Glucose and Galactose at C4) are called:
Correct Answer: C (Epimers)
Epimers are diastereomers that differ in stereochemical configuration at only one chiral center. D-Galactose is the C-4 epimer of D-Glucose.
Epimers are diastereomers that differ in stereochemical configuration at only one chiral center. D-Galactose is the C-4 epimer of D-Glucose.
11. Which carbon in D-Glucose is the C-2 epimer partner to D-Mannose?
Correct Answer: A (Carbon-2)
D-Mannose differs from D-Glucose solely in the spatial orientation of the -OH group at the C-2 position.
D-Mannose differs from D-Glucose solely in the spatial orientation of the -OH group at the C-2 position.
12. Alpha-D-glucose and Beta-D-glucose are examples of:
Correct Answer: A (Anomers)
Anomers differ only in configuration at the anomeric carbon (C1 for aldoses, C2 for ketoses) created upon cyclic hemiacetal/hemiketal ring closure.
Anomers differ only in configuration at the anomeric carbon (C1 for aldoses, C2 for ketoses) created upon cyclic hemiacetal/hemiketal ring closure.
13. The spontaneous change in the specific optical rotation of an optically active sugar solution until reaching equilibrium is called:
Correct Answer: B (Mutarotation)
Mutarotation occurs as alpha and beta anomers interconvert via the transient open-chain intermediate in aqueous solution.
Mutarotation occurs as alpha and beta anomers interconvert via the transient open-chain intermediate in aqueous solution.
14. What is the primary storage polysaccharide found in animals and humans?
Correct Answer: C (Glycogen)
Glycogen is a highly branched homopolymer of glucose stored primarily in liver and skeletal muscle tissues.
Glycogen is a highly branched homopolymer of glucose stored primarily in liver and skeletal muscle tissues.
15. What type of glycosidic linkages form the branch points in glycogen and amylopectin?
Correct Answer: B (Alpha-(1→6))
Linear chains contain alpha-(1→4) bonds, while branch points occur via alpha-(1→6) glycosidic bonds every 8-12 residues in glycogen.
Linear chains contain alpha-(1→4) bonds, while branch points occur via alpha-(1→6) glycosidic bonds every 8-12 residues in glycogen.
16. Plant starch is composed of which two structural polysaccharides?
Correct Answer: A (Amylose (unbranched) and Amylopectin (branched))
Starch is a mixture of linear helical amylose (~20%) and branched amylopectin (~80%).
Starch is a mixture of linear helical amylose (~20%) and branched amylopectin (~80%).
17. Why cannot humans digest cellulose as a nutrient?
Correct Answer: C (Humans lack the enzyme cellulase to hydrolyze beta-(1→4) bonds)
Human digestive enzymes (amylases) only cleave alpha-(1→4) linkages, so cellulose passes through as dietary fiber.
Human digestive enzymes (amylases) only cleave alpha-(1→4) linkages, so cellulose passes through as dietary fiber.
18. What is the universal chemical screening test used to detect all carbohydrates in a solution?
Correct Answer: A (Molisch’s Test)
Molisch’s reagent (alpha-naphthol with sulfuric acid) dehydrates carbohydrates to furfurals, producing a distinctive purple/violet ring at the interface.
Molisch’s reagent (alpha-naphthol with sulfuric acid) dehydrates carbohydrates to furfurals, producing a distinctive purple/violet ring at the interface.
19. Which qualitative test specifically differentiates reducing monosaccharides from reducing disaccharides based on reaction speed?
Correct Answer: B (Barfoed’s Test)
Barfoed’s reagent (copper acetate in acidic solution) is reduced rapidly by monosaccharides within 2-3 minutes, while disaccharides react much slower.
Barfoed’s reagent (copper acetate in acidic solution) is reduced rapidly by monosaccharides within 2-3 minutes, while disaccharides react much slower.
20. Seliwanoff’s test is used biochemically to distinguish:
Correct Answer: A (Ketoses from Aldoses)
Seliwanoff’s test uses resorcinol and HCl; ketohexoses dehydrate rapidly to yield a deep cherry-red color, whereas aldohexoses react much more slowly.
Seliwanoff’s test uses resorcinol and HCl; ketohexoses dehydrate rapidly to yield a deep cherry-red color, whereas aldohexoses react much more slowly.
21. Bial’s test uses orcinol and ferric chloride to selectively detect which class of sugars?
Correct Answer: B (Pentoses)
Bial’s reagent reacts with furfurals produced from pentose sugars (like ribose and xylose) to yield a characteristic blue-green condensation product.
Bial’s reagent reacts with furfurals produced from pentose sugars (like ribose and xylose) to yield a characteristic blue-green condensation product.
22. What characteristic color develops when an aqueous solution of amylose reacts with Lugol’s iodine reagent?
Correct Answer: A (Deep Blue-Black)
Iodine (polyiodide ions) slips inside the helical coils of unbranched amylose chains to form a deep blue-black charge-transfer complex.
Iodine (polyiodide ions) slips inside the helical coils of unbranched amylose chains to form a deep blue-black charge-transfer complex.
23. Inulin is a storage homopolysaccharide composed entirely of which monomeric sugar units?
Correct Answer: C (D-Fructose)
Inulin is a fructan (polymer of beta-D-fructose) used clinically to assess renal glomerular filtration rate (GFR).
Inulin is a fructan (polymer of beta-D-fructose) used clinically to assess renal glomerular filtration rate (GFR).
24. Chitin, which forms the exoskeleton of arthropods and fungal cell walls, is a linear polymer of:
Correct Answer: A (N-Acetylglucosamine (NAG))
Chitin is a structural homopolymer of N-acetyl-D-glucosamine residues connected by beta-(1→4) glycosidic bonds.
Chitin is a structural homopolymer of N-acetyl-D-glucosamine residues connected by beta-(1→4) glycosidic bonds.
25. A six-membered carbohydrate ring structure is structurally designated as a:
Correct Answer: A (Pyranose ring)
Six-membered cyclic sugars containing five carbons and one oxygen atom are named pyranoses due to resemblance to pyran.
Six-membered cyclic sugars containing five carbons and one oxygen atom are named pyranoses due to resemblance to pyran.
26. A five-membered carbohydrate ring structure (such as in cyclic ribose) is called a:
Correct Answer: B (Furanose ring)
Five-membered cyclic hemiacetals/hemiketals containing four carbons and one oxygen atom are called furanoses due to resemblance to furan.
Five-membered cyclic hemiacetals/hemiketals containing four carbons and one oxygen atom are called furanoses due to resemblance to furan.
27. Which form of stereoisomerism is determined by the configuration of the asymmetric carbon farthest from the carbonyl group?
Correct Answer: A (D- and L- stereoisomerism)
For hexoses, the configuration of the -OH group at C-5 (penultimate carbon) defines whether the sugar is D (right) or L (left), referenced against D-glyceraldehyde.
For hexoses, the configuration of the -OH group at C-5 (penultimate carbon) defines whether the sugar is D (right) or L (left), referenced against D-glyceraldehyde.
28. Most naturally occurring and physiologically active monosaccharides in human metabolic pathways belong to the:
Correct Answer: A (D-configuration)
Virtually all mammalian enzymes have evolved absolute stereospecificity for D-sugars (in contrast to L-amino acids for proteins).
Virtually all mammalian enzymes have evolved absolute stereospecificity for D-sugars (in contrast to L-amino acids for proteins).
29. Non-superimposable mirror-image isomers of a chiral carbohydrate (e.g., D-Glucose and L-Glucose) are termed:
Correct Answer: C (Enantiomers)
Enantiomers are optical isomers that are exact, non-superimposable mirror reflections of each other with inverted stereocenters at every chiral carbon.
Enantiomers are optical isomers that are exact, non-superimposable mirror reflections of each other with inverted stereocenters at every chiral carbon.
30. What is the total number of optical stereoisomers possible for an aldohexose with 4 chiral centers?
Correct Answer: B (16)
Using van ‘t Hoff’s rule (2^n, where n is chiral carbons): 2^4 = 16 distinct stereoisomers (8 D-aldoses and 8 L-aldoses).
Using van ‘t Hoff’s rule (2^n, where n is chiral carbons): 2^4 = 16 distinct stereoisomers (8 D-aldoses and 8 L-aldoses).
31. What sugar alcohol is formed by the enzymatic reduction of D-Glucose?
Correct Answer: A (Sorbitol (Glucitol))
Aldose reductase reduces glucose to sorbitol; excess intracellular accumulation of sorbitol contributes to diabetic cataracts and neuropathy.
Aldose reductase reduces glucose to sorbitol; excess intracellular accumulation of sorbitol contributes to diabetic cataracts and neuropathy.
32. Oxidation of only the terminal carbon (C6) of D-glucose yields which biologically important uronic acid?
Correct Answer: B (D-Glucuronic acid)
Oxidizing the C6 primary alcohol of glucose yields D-glucuronic acid, which participates in hepatic phase II detoxification/conjugation reactions.
Oxidizing the C6 primary alcohol of glucose yields D-glucuronic acid, which participates in hepatic phase II detoxification/conjugation reactions.
33. Trehalose, a disaccharide found in insect hemolymph and yeast, consists of:
Correct Answer: A (Two Glucose molecules linked by an alpha-(1→1) glycosidic bond)
Trehalose links both anomeric carbons (alpha-1,1), making it a non-reducing disaccharide that protects against desiccation.
Trehalose links both anomeric carbons (alpha-1,1), making it a non-reducing disaccharide that protects against desiccation.
34. Which of the following is a structural heteropolysaccharide (Glycosaminoglycan) acting as a natural anticoagulant?
Correct Answer: B (Heparin)
Heparin is a heavily sulfated glycosaminoglycan (GAG) that activates antithrombin III to inhibit coagulation proteases.
Heparin is a heavily sulfated glycosaminoglycan (GAG) that activates antithrombin III to inhibit coagulation proteases.
35. Hyaluronic acid is an unsulfated glycosaminoglycan composed of repeating disaccharide units of:
Correct Answer: A (D-Glucuronic acid and N-Acetylglucosamine)
Hyaluronan provides synovial joint lubrication, shock absorption, and tissue hydration in extracellular matrices.
Hyaluronan provides synovial joint lubrication, shock absorption, and tissue hydration in extracellular matrices.
36. The bacterial cell wall consists of a mesh-like macromolecule called peptidoglycan (murein), which features alternating units of:
Correct Answer: A (NAG (N-acetylglucosamine) and NAM (N-acetylmuramic acid))
Peptidoglycan consists of alternating beta-(1→4)-linked NAG and NAM cross-linked by short peptide chains.
Peptidoglycan consists of alternating beta-(1→4)-linked NAG and NAM cross-linked by short peptide chains.
37. Which pentose sugar forms the carbohydrate backbone of Ribonucleic Acid (RNA)?
Correct Answer: A (D-Ribose)
D-ribose is an aldopentose forming the furanose ribosyl rings in RNA, ATP, NAD+, and CoA.
D-ribose is an aldopentose forming the furanose ribosyl rings in RNA, ATP, NAD+, and CoA.
38. How does 2-deoxy-D-ribose in DNA differ structurally from D-ribose?
Correct Answer: A (It lacks an oxygen atom at Carbon-2 (-H instead of -OH))
Deoxyribose has a hydrogen atom instead of a hydroxyl group at C2, making DNA more resistant to alkaline hydrolysis than RNA.
Deoxyribose has a hydrogen atom instead of a hydroxyl group at C2, making DNA more resistant to alkaline hydrolysis than RNA.
39. When reducing sugars react with phenylhydrazine, characteristic crystalline derivatives are formed called:
Correct Answer: A (Osazones)
Reaction of reducing sugars with excess phenylhydrazine at C1 and C2 produces insoluble, yellow crystalline osazones with distinct crystal structures.
Reaction of reducing sugars with excess phenylhydrazine at C1 and C2 produces insoluble, yellow crystalline osazones with distinct crystal structures.
40. Which trio of sugars yields identical needle-shaped osazone crystals due to having identical stereochemistry from C3 to C6?
Correct Answer: A (Glucose, Fructose, and Mannose)
Because phenylhydrazine masks differences at C1 and C2, D-glucose, D-fructose, and D-mannose form the exact same glucosazone crystals.
Because phenylhydrazine masks differences at C1 and C2, D-glucose, D-fructose, and D-mannose form the exact same glucosazone crystals.
41. What is “Invert Sugar”?
Correct Answer: A (An equimolar mixture of glucose and fructose formed by hydrolyzing sucrose)
Hydrolysis changes the optical rotation from dextrorotatory (+66.5°) to levorotatory (-22°) due to the strong levorotation of free fructose (-92°).
Hydrolysis changes the optical rotation from dextrorotatory (+66.5°) to levorotatory (-22°) due to the strong levorotation of free fructose (-92°).
42. Which transport protein facilitates insulin-dependent glucose uptake into skeletal muscle and adipose cells?
Correct Answer: D (GLUT4)
GLUT4 is the regulated glucose transporter that translocates to the plasma membrane in response to insulin signaling.
GLUT4 is the regulated glucose transporter that translocates to the plasma membrane in response to insulin signaling.
43. What is the sweetest naturally occurring sugar among standard dietary carbohydrates?
Correct Answer: C (Fructose)
Fructose has the highest relative sweetness score (~170 relative to sucrose at 100), making it the sweetest natural monosaccharide.
Fructose has the highest relative sweetness score (~170 relative to sucrose at 100), making it the sweetest natural monosaccharide.
44. Glycoproteins possess oligosaccharide chains covalently attached to polypeptide side chains via which two linkages?
Correct Answer: A (N-linked (Asparagine) and O-linked (Serine/Threonine))
N-glycosylation attaches to the amide nitrogen of asparagine; O-glycosylation attaches to the hydroxyl oxygen of serine or threonine.
N-glycosylation attaches to the amide nitrogen of asparagine; O-glycosylation attaches to the hydroxyl oxygen of serine or threonine.
45. Blood group antigen specificity (A, B, O) on human erythrocytes is determined by unique oligosaccharide sequences terminating in:
Correct Answer: A (Specific terminal monosaccharides added to the H-antigen core)
Type A adds N-acetylgalactosamine, Type B adds D-galactose, and Type O has unmodified H-antigen.
Type A adds N-acetylgalactosamine, Type B adds D-galactose, and Type O has unmodified H-antigen.
46. Which structural polysaccharide is extracted from red marine algae and used widely in laboratories as a solidifying culture medium?
Correct Answer: A (Agar (Agarose))
Agar is a sulfated galactan polymer derived from Rhodophyta algae, highly valued for its inert gelling properties in microbiological media and electrophoresis.
Agar is a sulfated galactan polymer derived from Rhodophyta algae, highly valued for its inert gelling properties in microbiological media and electrophoresis.
47. Dextrans are high-molecular-weight branched glucose polymers synthesized by dental bacteria (like Streptococcus mutans) via:
Correct Answer: A (Predominantly alpha-(1→6) linkages with alpha-(1→3) branches)
Dextrans form sticky dental plaque and are also used clinically as plasma volume expanders.
Dextrans form sticky dental plaque and are also used clinically as plasma volume expanders.
48. Which digestive enzyme present in saliva and pancreatic juice initiates starch breakdown into maltose and dextrins?
Correct Answer: A (Alpha-Amylase (Ptyalin))
Alpha-amylase is an endoglycosidase that hydrolyzes internal alpha-(1→4) glycosidic bonds in starch and glycogen.
Alpha-amylase is an endoglycosidase that hydrolyzes internal alpha-(1→4) glycosidic bonds in starch and glycogen.
49. Galactosemia is an inherited metabolic disease most commonly caused by a congenital deficiency of which enzyme?
Correct Answer: A (Galactose-1-phosphate uridylyltransferase (GALT))
Classic galactosemia results from GALT deficiency, causing toxic accumulation of galactose-1-phosphate and galactitol leading to cataracts and liver damage.
Classic galactosemia results from GALT deficiency, causing toxic accumulation of galactose-1-phosphate and galactitol leading to cataracts and liver damage.
50. Which high-energy phosphorylated carbohydrate intermediate enters the first step of the glycolytic pathway?
Correct Answer: A (Glucose-6-phosphate (G6P))
Hexokinase/glucokinase phosphorylates free D-glucose into glucose-6-phosphate (G6P), trapping it inside the cell for glycolysis or glycogenesis.
Hexokinase/glucokinase phosphorylates free D-glucose into glucose-6-phosphate (G6P), trapping it inside the cell for glycolysis or glycogenesis.