CHAPTER 1 : BIOLOGY 1 SB015
SEMESTER 1
MOLECULE OF LIFE
1.2 : CARBOHYDRATES
LEARNING OUTCOMES
a) State the classes of carbohydrates such as
monosaccharides, disaccharides and
polysaccharides.
b) Illustrate the formation and
breakdown of maltose.
c) Compare the structures and
functions of starch, glycogen and
cellulose.
1
MACROMOLECULES
• Are called macromolecules because all are
large size molecules.
• Consist of many repeating units forming
polymer.
• Each repeating unit is monomer.
Macromolecules Monomer Polymer
Carbohydrates Monosaccharide Polysaccharide
Proteins Amino acid Polypeptide
Nucleic acids Nucleotide Polynucleotide
CLASSIFICATION OF CARBOHYDRATES
⮚ Composed of Carbon (C), Hydrogen (H) & Oxygen (O) atoms
in ratio of 1:2:1
⮚ Molecular formula is (CH2O)n ; n = number of carbon atom
CLASSES
Single/simple sugars units (monomers)
which make up all other carbohydrates;
Monosaccharides cannot be further hydrolyzed into
smaller units.
Consists of two monosaccharides joined
by a glycosidic bond in condensation
Disaccharides
reaction
Polymers of many monosaccharides
joined by glycosidic bonds in
Polysaccharides
condensation reaction
Carbohydrates
Monosaccharide Disaccharide Polysaccharide
(monomer) (dimer) (polymer)
Glucose Maltose Starch
Fructose Sucrose Glycogen
Galactose Lactose Cellulose
CLASS OF CARBOHYDRATES
1) Monosaccharides
⮚ Molecular formula is (CH2O)n ;
n = number of carbon (3 < n < 6)
⮚ e.g. the molecular formula for glucose that
has six carbon is C6H12O6
Importance of monosacharide:
Monomer for disaccharide and
polysaccharide.
Characteristics of Monosaccharide
⮚ Sweet taste
⮚ Soluble in water
⮚ Can be crystallized
⮚ Cannot be broken down to
simpler molecule
⮚ Reducing sugar
⮚ Isomeric molecule (e.g.
glucose and fructose)
Monosaccharide as Reducing Sugar
• All monosaccharides are reducing sugars
because they have free functional / carbonyl
group.
Figure: Free aldehyde group in glucose molecule
Monosaccharide is Isomeric Molecule
Isomers are molecules that have the same
chemical formula (C6H12O6) but with different
molecular structures.
CLASSIFICATION OF MONOSACCHARIDE
Location of the Number of
carbonyl group carbon
Aldose Ketose Triose Pentose Hexose
Carbonyl Carbonyl
group at C1 group at C2
n=3 n=5 n=6
Linear Chain of MONOSACCHARIDES
**Though often drawn as linear skeletons,
in aqueous solutions many sugars form rings
Example Of Monosaccharides :
Glucose
⮚ The MOST common monosaccharides.
⮚ MORE stable in ring form.
Importance of glucose:
i. Main respiratory substrate in plants and
animal.
ii. Main source of energy for cells.
Two Types of Glucose
α-glucose β-glucose
Position of -OH differ on carbon number 1
Other Examples of Monosaccharides
Fructose Galactose
CLASS OF CARBOHYDRATES
2) Disaccharides
⮚ Molecular formula C12H22O11
⮚ Consists of TWO monosaccharides joined
by glycosidic linkage
⮚ Formation of glycosidic linkage through
condensation (loss / removal of water)
⮚ Breakdown of glycosidic linkage through
hydrolysis (addition of water)
CONDENSATION
Energy is absorbed
New bond is formed
One water
molecule is lost /
removed
Hydrolysis
Existing bond is broken down
One water
molecule is
required
Energy is released
Characteristics of Disaccharides
⮚Sweet taste
⮚Soluble in water
⮚Can be crystallized
⮚Some are:
• reducing sugar
(e.g. maltose, lactose)
• non reducing sugar
(e.g. sucrose)
Three Examples of Disaccharides
Disaccharide Monomers Chemical bond between
monomers
Maltose α-glucose + α-1,4 glycosidic linkage
(Malt sugar) α-glucose
Sucrose α-glucose + α-1,2 glycosidic linkage
(Cane sugar) fructose
Lactose β-galactose + β-1,4 glycosidic linkage
(Milk sugar) α-glucose
Formation & Breakdown of Maltose
Condensation
α−glucose + α−glucose Maltose + Water
Hydrolysis
Condensation
+ H2O
Hydrolysis
α-1,4 glycosidic linkage
Formation of Maltose
Condensation
α−glucose + α−glucose Maltose + Water
Condensation
+ H2O
α-1,4 glycosidic linkage
Breakdown of Maltose
Hydrolysis
Maltose + Water α−glucose + α−glucose
Hydrolysis
α-1,4 glycosidic linkage
CLASS OF CARBOHYDRATES
3) Polysaccharides
⮚Molecular formula (C6H10O5)n;
n = number of monosaccharides / monomers
⮚Polymers with hundreds to thousands of
monosaccharides joined by glycosidic
linkages through polymerization
Polymerization refers to condensation
of many monosaccharides
Characteristics of Polysaccharides
⮚ Has no sweet taste
⮚ Insoluble in water
⮚ Cannot be crystallized
⮚ Non-reducing sugar
⮚ Can be hydrolyzed to simpler molecule
(e.g. starch, glycogen)
Examples of Polysaccharides
Polysaccharides
monomer is
α-glucose β-glucose
Cellulose
Plant Animal
storage sugar storage sugar
Starch Glycogen
unbranched branched
Amylose Amylopectin
Function of Starch
⮚Main carbohydrate storage in plants
Characteristics of Starch
⮚Insoluble in water.
⮚Easily breakdown to the simplest form.
⮚Does not affect water potential.
⮚High energy molecule because it is large
size molecule.
Why is starch suitable as storage material ?
Structure of Starch
⮚Monomer for starch is α-glucose
⮚Consist of amylose and amylopectin
(1) Amylose
⮚Consist of short chain of α-glucose which
contains 200-15000 monomers.
⮚Each α-glucose is joined by α-1,4 glycosidic
linkage.
⮚Form unbranched helical chain.
⮚Helical structure is maintained by hydrogen
bond.
⮚Soluble in hot water.
(1) Amylose
α-1,4 glycosidic
linkage
hydrogen bond can
form with other
monomer at these
points.
(2) Amylopectin
⮚Consist of short chain of α-glucose which
contains 2000-200000 monomers.
⮚Each α-glucose is joined by α-1,4 glycosidic
linkage.
⮚Form branched helical chain.
Branching occurs at 25 – 30 unit of α-glucose
held by α-1,6 glycosidic linkage.
⮚Helical structure is maintained by hydrogen
bond.
⮚Not water soluble.
(2) Amylopectin
α-1,4 glycosidic
linkage
α-1,6 glycosidic
linkage
(2) Amylopectin
α-1,6 glycosidic
linkage
α-1,4 glycosidic linkage
Function of Glycogen
⮚Main carbohydrate storage in animals
*Mostly found in liver cells and muscle cells
Glycogen
Accumulation of glycogen in hepatocytes.
Characteristics of Glycogen
⮚Insoluble in water.
⮚Does not affect water potential.
⮚Large/compact/highly branched molecule.
Why do animals cell store energy in form of
glycogen not glucose?
Structure of Glycogen
⮚Consist of α-glucose monomer
⮚Each α-glucose joined by α-1,4 glycosidic
linkage (linear) and α-1,6 glycosidic linkage
(branch)
⮚Highly branched chain.
Branching occurs at every 8 – 10 units of
α-glucose.
⮚Not water soluble.
Structure of Glycogen
α-1,6 glycosidic
linkage
α-1,4 glycosidic
linkage
α-1,6 glycosidic
linkage
Structure of Glycogen
Branching occurs at every 8
– 10 units of α-glucose.
Function of Cellulose
⮚Major component of plant cell wall that
provide the structural support.
Structure of Cellulose
⮚Made up of β-glucose monomer.
⮚ Long, straight and unbranched chain.
⮚Each β-glucose monomer is joined by β-1,4
glycosidic linkage.
⮚Each chain is arranged parallel to other
chain by hydrogen bond.
Structure of Cellulose
Hydrogen bond *Between O atom on C3 and H
atom on C6
β-1,4 glycosidic
linkage
Polysaccharides in plants and animals
41
(SUMMARY)
linkage
42
QUESTION :
Think about it?
• How ruminant/herbivorous animals
obtain nutrients from cellulose they
eat?
• How about human?
