Tutorial 12 — Carbohydrates

Note: This tutorial PDF consists primarily of scanned images. The questions below are reconstructed based on typical FAD1018 Tutorial 12 content on Carbohydrates.

Learning Outcomes

Classify carbohydrates (monosaccharides, disaccharides, polysaccharides)
Understand stereochemistry of sugars (D/L, α/β)
Learn ring structures (Haworth projections)
Identify reducing vs non-reducing sugars
Understand carbohydrate reactions

Part A: Classification of Carbohydrates

Question 1

a) Define carbohydrate and give the general formula.

b) Classify carbohydrates based on the number of carbon atoms:

Trioses (3C)
Tetroses (4C)
Pentoses (5C)
Hexoses (6C)

c) Give one example of each type with its structure.

Question 2

a) Distinguish between:

Aldoses and ketoses
Monosaccharides, disaccharides, and polysaccharides

b) Classify the following:

Glucose
Fructose
Sucrose
Starch
Ribose
Maltose

Part B: Stereochemistry of Monosaccharides

Question 3

a) What is the difference between D- and L- sugars?

b) How do you determine if a sugar is D- or L- configuration?

c) Draw the Fischer projection of D-glucose and L-glucose.

d) Identify the number of stereoisomers possible for:

Aldotetroses
Aldopentoses
Aldohexoses

Question 4

a) Define epimers. Give examples.

b) D-glucose and D-mannose are epimers at which carbon?

c) D-glucose and D-galactose are epimers at which carbon?

d) Draw the structures showing these relationships.

Part C: Cyclic Structures (Haworth Projections)

Question 5

a) Explain mutarotation using glucose as an example.

b) Draw the Haworth projection for:

α-D-glucopyranose
β-D-glucopyranose

c) What is the anomeric carbon? How does it differ in α and β forms?

d) What are the approximate percentages of α and β forms at equilibrium?

Question 6

a) Draw the Haworth structure of:

α-D-fructofuranose
β-D-fructofuranose

b) Why does fructose form a furanose ring while glucose prefers pyranose?

c) Convert the following Fischer projection to Haworth:

   CHO
    |
H-C-OH
    |
HO-C-H
    |
H-C-OH
    |
H-C-OH
    |
   CH2OH

(D-mannose)

Part D: Disaccharides

Question 7

a) Define glycosidic bond.

b) Draw the structure of maltose showing:

The monosaccharide units
The glycosidic linkage (α-1,4)
Whether it is a reducing sugar

c) Explain why maltose is a reducing sugar.

Question 8

a) Draw the structure of sucrose.

b) Identify the glycosidic linkage in sucrose.

c) Why is sucrose a non-reducing sugar?

d) What products are formed when sucrose is hydrolyzed?

Question 9

a) Compare and contrast lactose, maltose, and sucrose:

Monosaccharide units
Glycosidic linkages
Reducing/non-reducing
Sources

b) What is lactose intolerance?

Part E: Reactions of Carbohydrates

Question 10

a) What is the Benedict's test? Which sugars give a positive result?

b) Write the reaction of glucose with Benedict's reagent.

c) What color change indicates a positive test?

Question 11

a) Describe the iodine test for starch.

b) What color is observed with:

Starch
Glycogen
Cellulose

c) Explain the structural basis for the iodine-starch complex.

Question 12

a) What is the Osazone formation? What is its significance?

b) Which sugars form the same osazone?

c) Why is glucose and fructose said to form identical osazones?

Part F: Polysaccharides

Question 13

a) Compare starch and cellulose:

Monomer units
Glycosidic linkages
Function in nature
Digestibility by humans

b) Draw a segment of:

Amylose (showing α-1,4 linkages)
Cellulose (showing β-1,4 linkages)

c) Why can't humans digest cellulose?

Question 14

a) Compare glycogen and starch:

Structure
Function
Location in organisms

b) Why is glycogen more highly branched than amylopectin?

Key Concepts

Monosaccharide — Simple sugar (single unit)
Disaccharide — Two monosaccharide units linked
Polysaccharide — Many monosaccharide units
Aldose — Sugar with aldehyde group
Ketose — Sugar with ketone group
Pyranose — Six-membered ring sugar
Furanose — Five-membered ring sugar
Anomeric Carbon — Carbon that becomes chiral in cyclic form
Glycosidic Bond — Linkage between sugar units
Reducing Sugar — Sugar that can reduce other compounds
Mutarotation — Interconversion of α and β anomers

Summary Table: Common Carbohydrates

Carbohydrate	Type	Units	Linkage	Reducing?
Glucose	Monosaccharide	-	-	Yes
Fructose	Monosaccharide	-	-	Yes
Maltose	Disaccharide	Glu+Glu	α-1,4	Yes
Lactose	Disaccharide	Gal+Glu	β-1,4	Yes
Sucrose	Disaccharide	Glu+Fru	α,β-1,2	No
Starch	Polysaccharide	Glucose	α-1,4; α-1,6	-
Cellulose	Polysaccharide	Glucose	β-1,4	-
Glycogen	Polysaccharide	Glucose	α-1,4; α-1,6	-

FAD1018 Tutorial 12 — Carbohydrates