Lecture 5

Fill in the Blanks

1. Carbohydrates are composed of carbon, hydrogen, and __________.

Answer: oxygen
2. The bond between the anomeric carbon of one sugar and any –OH group of another
sugar is called a __________ bond.
Answer: glycosidic
3. A 1→4' glycosidic linkage means the anomeric carbon of the first sugar is bonded to the
__________ carbon of the second sugar.
Answer: C4
4. A 1→6' glycosidic linkage involves the anomeric carbon of the first sugar and the
__________ carbon of the second sugar.
Answer: C6
5. A 1→1' glycosidic linkage joins the __________ carbons of both sugars.
Answer: anomeric
6. Maltose is commonly known as __________ sugar.
Answer: malt
7. Maltose is found in __________ grain, especially barley.
Answer: germinating
8. Maltose is a __________ sugar.
Answer: reducing
9. Sucrose is commonly known as __________ sugar.
Answer: table
10. Sucrose is abundant in __________ and sugar beets.
Answer: sugarcane
11. In sucrose, glucose and fructose are joined by a __________ linkage.
Answer: glycosidic
12. Sucrose is a __________ sugar because it has no free anomeric carbon.
Answer: non-reducing
13. Under acidic conditions, sucrose is hydrolyzed to form __________ and __________.
Answer: glucose, fructose
14. The hydrolysis product of sucrose is known as __________ sugar.
Answer: invert
15. Invert sugar is __________ than sucrose.
Answer: sweeter
16. Lactose is commonly called __________ sugar.
Answer: milk
17. The enzyme that digests lactose is called __________.
Answer: lactase
18. Oligosaccharides contain __________ to __________ monosaccharide units.
Answer: 3, 10
19. Raffinose is an example of a(n) __________.
Answer: oligosaccharide
20. Raffinose is made up of galactose, glucose, and __________.
Answer: fructose
21. Starch is a polymer of __________.
Answer: D-glucose
22. The two main components of starch are __________ and __________.
Answer: amylose, amylopectin
23. Amylose has a __________ structure.
Answer: linear
24. Amylose is linked by __________ glycosidic bonds.
Answer: α(1→4)
25. Amylopectin is __________ in structure.
Answer: branched
26. Amylopectin contains both α(1→4) and α(1→__) glycosidic bonds.
Answer: 6
27. Glycogen is a storage polysaccharide in __________.
Answer: animals
28. Glycogen is structurally similar to __________.
Answer: amylopectin
29. Glycogen has more frequent __________ than amylopectin.
Answer: branching
30. In ring formation of sugars, an aldehyde reacts with an alcohol to form a __________.
Answer: hemiacetal
31. A ketone reacts with an alcohol to form a __________.
Answer: hemiketal
32. A glycosidic bond can occur via __________ or __________ linkages.
Answer: O-, N-
33. The difference between α- and β-glycosidic bonds lies in the configuration at the
__________ carbon.
Answer: anomeric
34. α-linkages are generally __________ by humans.
Answer: digestible
35. β-linkages are generally __________ by humans.
Answer: indigestible
36. Cellulose contains __________(1→4) glycosidic bonds.
Answer: β
37. Amylose is __________ in water but forms thick colloidal suspensions.
Answer: insoluble
38. The glycosidic bond between two sugars is a __________ bond.
Answer: covalent
39. Melibiose is a disaccharide composed of galactose and __________.
Answer: glucose
40. The glycosidic bond in melibiose is an example of an α(1→__) linkage.
Answer: 6
41. In glycosidic bond formation, a molecule of __________ is eliminated.
Answer: water
42. Hydrolysis of starch produces __________.
Answer: maltose
43. The enzyme that hydrolyzes starch is called __________.
Answer: amylase
44. Glycogen is stored in the __________ and muscles.
Answer: liver
45. Glycogen is also called __________ starch.
Answer: animal
46. Invert sugar is commonly used in __________ production.
Answer: confectionery
47. Lactose is a __________ sugar.
Answer: reducing
48. In disaccharides, the bond between sugars is called a __________ bond.
Answer: glycosidic
49. Oligosaccharides may be found in legumes like __________.
Answer: beans
 50. α-glycosidic bonds cause a __________ configuration of the sugar chain.
Answer: helical
51. β-glycosidic bonds result in a __________ chain structure.
Answer: linear
52. Amylopectin branches occur at every __________ glucose units.
Answer: 24–30
53. Glycogen branches occur every __________ glucose units.
Answer: 8–12
54. Starch is a major carbohydrate in the human __________.
Answer: diet
55. The digestion of carbohydrates begins in the __________.
Answer: mouth
56. The general formula of carbohydrates is __________.
Answer: Cn(H2O)n
57. Sugars with five carbon atoms are called __________.
Answer: pentoses
58. Sugars with six carbon atoms are called __________.
Answer: hexoses
59. Glucose is a(n) __________ sugar.
Answer: aldohexose
60. Fructose is a(n) __________ sugar.
Answer: ketohexose

Multiple Choice Questions

1. What type of glycosidic linkage connects glucose units in amylose?

a) α(1→6)
b) β(1→4)
c) α(1→4)
d) β(1→6)
✔ Answer: c) α(1→4)

2. Which disaccharide is a non-reducing sugar?

a) Maltose
b) Lactose
c) Sucrose
d) Cellobiose
✔ Answer: c) Sucrose

3. Raffinose is an example of a(n):

a) Monosaccharide
b) Disaccharide
c) Oligosaccharide
d) Polysaccharide
✔ Answer: c) Oligosaccharide
4. The enzyme that digests lactose is:

a) Amylase
b) Sucrase
c) Lactase
d) Maltase
✔ Answer: c) Lactase

5. Which sugar yields glucose and fructose on hydrolysis?

a) Lactose
b) Maltose
c) Sucrose
d) Cellulose
✔ Answer: c) Sucrose

6. Which sugar is a reducing sugar?

a) Sucrose
b) Lactose
c) Amylose
d) Amylopectin
✔ Answer: b) Lactose

7. Glycogen is stored mainly in:

a) Blood
b) Brain
c) Liver and muscle
d) Kidney and pancreas
✔ Answer: c) Liver and muscle

8. Which glycosidic bond is found in cellulose?

a) α(1→4)
b) α(1→6)
c) β(1→4)
d) β(1→6)
✔ Answer: c) β(1→4)

9. What kind of bond is a glycosidic bond?

a) Ionic
b) Peptide
c) Covalent
d) Hydrogen
✔ Answer: c) Covalent
10. What makes invert sugar sweeter than sucrose?

a) Higher molecular weight

b) Presence of maltose
c) Presence of free monosaccharides
d) Presence of cellulose
✔ Answer: c) Presence of free monosaccharides

11. Which component of starch is branched?

a) Amylose
b) Amylopectin
c) Glycogen
d) Cellulose
✔ Answer: b) Amylopectin

12. What is the product of hydrolysis of maltose?

a) Sucrose
b) Fructose
c) Glucose
d) Galactose
✔ Answer: c) Glucose

13. Glycogen has branches every:

a) 6–8 glucose units

b) 12–14 glucose units
c) 8–12 glucose units
d) 20–25 glucose units
✔ Answer: c) 8–12 glucose units

14. A 1→6 glycosidic linkage is responsible for:

a) Linear structure
b) Sweet taste
c) Branching
d) Reduction
✔ Answer: c) Branching

15. The glycosidic bond between two glucose units is formed by:

a) Hydrolysis
b) Condensation
c) Oxidation
d) Reduction
✔ Answer: b) Condensation
16. Which sugar polymer is digestible by humans?

a) Cellulose
b) Amylose
c) Chitin
d) β-glucan
✔ Answer: b) Amylose

17. Which of the following is the sweetest sugar?

a) Glucose
b) Sucrose
c) Fructose
d) Galactose
✔ Answer: c) Fructose

18. Which polysaccharide is most similar in structure to glycogen?

a) Cellulose
b) Amylopectin
c) Amylose
d) Raffinose
✔ Answer: b) Amylopectin

19. What type of sugar is fructose?

a) Aldohexose
b) Ketohexose
c) Ketopentose
d) Aldopentose
✔ Answer: b) Ketohexose

20. In disaccharides, the bond formed is usually between the anomeric carbon and:

a) Hydrogen
b) Carbonyl group
c) Hydroxyl group
d) Amide group
✔ Answer: c) Hydroxyl group

21. What type of sugar is glucose?

a) Ketopentose
b) Aldopentose
c) Ketohexose
d) Aldohexose
✔ Answer: d) Aldohexose
22. Which of the following is NOT a disaccharide?

a) Sucrose
b) Lactose
c) Raffinose
d) Maltose
✔ Answer: c) Raffinose

23. The difference between α- and β-glycosidic bonds is based on the configuration of the:

a) C2 carbon
b) C4 carbon
c) Anomeric carbon
d) C6 carbon
✔ Answer: c) Anomeric carbon

24. The bond between a sugar and an amine group is called a:

a) O-glycosidic bond
b) N-glycosidic bond
c) Ester bond
d) Peptide bond
✔ Answer: b) N-glycosidic bond

25. Which of the following carbohydrates is highly branched?

a) Amylose
b) Amylopectin
c) Cellulose
d) Raffinose
✔ Answer: b) Amylopectin

26. A sugar that contains a ketone group is called a:

a) Ketose
b) Aldose
c) Reductose
d) Ketopentane
✔ Answer: a) Ketose

27. The glycosidic linkage in sucrose is between:

a) Glucose C1 and Fructose C4

b) Glucose C1 and Fructose C6
c) Glucose C1 and Fructose C2
d) Fructose C1 and Glucose C6
✔ Answer: c) Glucose C1 and Fructose C2
28. Which disaccharide gives a positive test for reducing sugars?

a) Sucrose
b) Lactose
c) None of these
d) Cellulose
✔ Answer: b) Lactose

29. What type of reaction breaks glycosidic bonds in carbohydrates?

a) Reduction
b) Hydrolysis
c) Oxidation
d) Hydrogenation
✔ Answer: b) Hydrolysis

30. What type of linkage is found at the branch points in glycogen?

a) α(1→4)
b) β(1→4)
c) α(1→6)
d) β(1→6)
✔ Answer: c) α(1→6)

31. Cellulose differs from starch because:

a) It contains α-glycosidic bonds

b) It is branched
c) It is composed of ketoses
d) It contains β(1→4) glycosidic bonds
✔ Answer: d) It contains β(1→4) glycosidic bonds

32. What happens during the formation of a glycosidic bond?

a) Water is added
b) A peptide is formed
c) Water is removed
d) A ketone group is introduced
✔ Answer: c) Water is removed

33. In which food would you most likely find raffinose?

a) White bread
b) Chicken
c) Legumes
d) Dairy products
✔ Answer: c) Legumes
34. What enzyme breaks down starch into maltose?

a) Lactase
b) Sucrase
c) Amylase
d) Cellulase
✔ Answer: c) Amylase

35. Which carbohydrate is commonly referred to as “milk sugar”?

a) Maltose
b) Lactose
c) Sucrose
d) Galactose
✔ Answer: b) Lactose

36. The enzyme that breaks β(1→4) linkages in lactose is:

a) Sucrase
b) Amylase
c) Lactase
d) Invertase
✔ Answer: c) Lactase

37. In humans, the enzyme cellulase is:

a) Active in the stomach

b) Found in saliva
c) Not produced
d) Found in the liver
✔ Answer: c) Not produced

38. Which of the following carbohydrates has the highest degree of branching?
a) Amylose
b) Cellulose
c) Amylopectin
d) Glycogen
✔ Answer: d) Glycogen

39. Which test distinguishes between reducing and non-reducing sugars?

a) Benedict’s test
b) Biuret test
c) Sudan III test
d) Iodine test
✔ Answer: a) Benedict’s test

40. Which carbohydrate is typically stored in plants?

a) Glycogen
b) Glucose
c) Amylose
d) Starch
✔ Answer: d) Starch
 Descriptive Questions

1. Define carbohydrates. Classify them with suitable examples.

Answer:
Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, generally in
the ratio Cn(H₂O)n. They are also known as saccharides and serve as energy sources,
structural materials, and signaling molecules.

Classification:

1. Monosaccharides – Single sugar unit (e.g., glucose, fructose)

2. Disaccharides – Two sugar units (e.g., sucrose, lactose, maltose)
3. Oligosaccharides – 3–10 sugar units (e.g., raffinose)
4. Polysaccharides – More than 10 units (e.g., starch, glycogen, cellulose)

2. Describe the structure and function of maltose, lactose, and sucrose.

Answer:

 Maltose: Composed of two glucose units linked by an α(1→4) glycosidic bond. It is a

reducing sugar, formed during starch digestion.
 Lactose: Composed of glucose and galactose joined by a β(1→4) glycosidic bond. Found
in milk; it is a reducing sugar.
 Sucrose: Composed of glucose and fructose linked by an α(1→β2) bond (both anomeric
carbons involved). It is a non-reducing sugar and is common in sugarcane.

3. What is a glycosidic bond? Explain types with examples.

Answer:
A glycosidic bond is a covalent bond formed between the anomeric carbon of a sugar and a
hydroxyl group of another molecule (another sugar, alcohol, or base).

Types:

 O-glycosidic bond: Anomeric carbon binds to –OH (e.g., maltose – α(1→4) linkage)
 N-glycosidic bond: Anomeric carbon binds to a nitrogen atom (e.g., nucleotide sugars)

Examples:

 Maltose: α(1→4) O-glycosidic bond

 Lactose: β(1→4) O-glycosidic bond
 Sucrose: α(1→β2) O-glycosidic bond
4. Differentiate between reducing and non-reducing sugars.

Answer:

Reducing Sugars Non-Reducing Sugars

Have a free anomeric carbon Anomeric carbons are involved in glycosidic bond

Can reduce metal ions (e.g., Cu²⁺) Cannot reduce metal ions

Give positive Benedict’s/Fehling’s test Do not give positive tests

Examples: glucose, maltose, lactose Example: sucrose

5. What is invert sugar? How is it formed and why is it sweeter than sucrose?

Answer:
Invert sugar is a mixture of glucose and fructose formed by acid or enzymatic hydrolysis of
sucrose. The process inverts the optical rotation from dextrorotatory to levorotatory, hence the
name.

Reaction:
Sucrose + H₂O → Glucose + Fructose

It is sweeter than sucrose due to the higher sweetness of fructose. It is used in the
confectionery industry to improve sweetness and moisture retention.

6. Describe the structure and biological significance of starch.

Answer:
Starch is a plant storage polysaccharide made of D-glucose units.

Components:

 Amylose: Linear polymer with α(1→4) linkages

 Amylopectin: Branched polymer with α(1→4) and α(1→6) linkages

Biological Significance:

 Major energy source in the human diet

 Digested by amylase enzymes to form glucose
 Stored in plant tissues like seeds, tubers, and roots
7. Compare amylose, amylopectin, and glycogen.

Answer:

Feature Amylose Amylopectin Glycogen

Structure Linear Branched Highly branched

Linkages α(1→4) α(1→4) and α(1→6) α(1→4) and α(1→6)

Solubility Low Higher than amylose Very high

Occurrence Plants Plants Animals (liver, muscle)

Branching freq. – Every 24–30 glucose units Every 8–12 glucose units

8. Explain the role and structure of glycogen in animals.

Answer:
Glycogen is the storage form of glucose in animals, primarily in the liver and muscles.

 It is a highly branched polysaccharide with α(1→4) chains and α(1→6) branches every
8–12 units.
 Allows rapid mobilization of glucose when energy is needed.
 Maintains blood glucose levels and supports muscle activity.

9. Why can humans digest starch but not cellulose?

Answer:
Humans can digest starch (amylose, amylopectin) because they have amylase, which breaks
α(1→4) bonds.

Humans cannot digest cellulose because:

 Cellulose contains β(1→4) glycosidic bonds

 Human digestive enzymes cannot hydrolyze β-linkages
 Thus, cellulose acts as dietary fiber
10. What are oligosaccharides? Mention their significance.

Answer:
Oligosaccharides are carbohydrates containing 3–10 monosaccharide units, joined by
glycosidic bonds.

Examples:

 Raffinose (galactose + glucose + fructose)

 Found in legumes, whole grains

Significance:

 Support gut microbiota

 May cause gas formation (fermented in colon)
 Contribute to cell recognition on surfaces (e.g., glycoproteins)

11. Describe the hydrolysis of disaccharides and name the enzymes involved.

Answer:

Disaccharide Products Enzyme

Sucrose Glucose + Fructose Sucrase/invertase

Maltose Glucose + Glucose Maltase

Lactose Glucose + Galactose Lactase

Hydrolysis is the addition of water to break the glycosidic bond using specific enzymes.

12. Explain the difference between homo- and heteropolysaccharides with examples.

Answer:

 Homopolysaccharides: Composed of one type of monosaccharide

o Examples: Starch, glycogen, cellulose (all from glucose)
 Heteropolysaccharides: Composed of more than one type of monosaccharide
o Examples: Hyaluronic acid, chondroitin sulfate (glucuronic acid + N-
acetylglucosamine)