Biomole
cules
Pt II: Carbohydrates
Carbohydrates
 Are
made from just three elements:
carbon, hydrogen and oxygen CHO
Functions of Carbohydrates
 Are
an important source of chemical
energy for organisms.
 Are used as energy reserves in plants
and animals.
 Form structural components such as
cell walls
 Form part of both DNA and RNA
 Combine with other macromolecules
to form glycoproteins and
glycolipids.
 Found
on the surface of EVERY CELL IN THE
BODY.
 Eg. Membrane glycoproteins identify cells and
are involved in cell-cell communication.
Classes of Carbohydrates

Carbohydrates are classified into classes
depending upon the number of linked sugar
molecules they contain.

Classes of Carbohydrates




Monosaccharides
Disaccharides
Polysaccharides
*diagram on boarf
Carbohydrates containing one or two sugar units
are often referred to as simple carbohydrates;
those containing many sugar molecules are called
complex carbohydrates
Simple Carbohydrates
Monosaccharides
General formula:
(CH2O)n
n=3, triose
n=5, pentose
n=6, hexose
Glucose
Fuel molecule
Fructose
Fuel molecule
Ribose
Component of the
nucleotide for RNA
Disaccharides
(common dietary
components)
Sucrose
(a glucose + b fructose)
Transport sugar in
vascular plants
Lactose
Component of milk
(b galactose + a glucose)
Maltose
(a glucose + a glucose)
Obtained in the
breakdown of
starch
Complex Carbohydrates
Polysaccharides
(insoluble
macromolecules)
Starch
Storage molecule in
plants
Glycogen
Storage molecule in
animals
Cellulose
Component of the
plant cell wall
Chitin
Component of the
exoskeletons of
insects and
crustaceans
Peptidoglycan
Component of
bacterial cell wall
More about monosaccharides
 Very
soluble.
 The most common and biologically
important simple sugar is glucose.
What’s so good about glucose?


Fuel molecule for the cell.
Building block for many
other important
carbohydrates.
Linking monosaccharides
 Linking
two monosaccharides results in
a disaccharide molecule.
 Repetitive linking of many
monosaccharides results in a
polysaccharide.
 The process of linking monosaccharide
monomers is referred to as
condensation reaction.
Condensation reaction


Disaccharides are formed via the condensation reaction.
Meaning water is produced as a by-product.
More about Polysaccharides
 Polysaccharides
categories:

are divided into two
Storage polysaccharides
 Starch
 Glycogen

Structural polysaccharides
 Cellulose
More about storage
polysaccharides

Starch

Fuel storage
polysaccharide in plants.
More about storage
polysaccharides

Glycogen

Fuel storage
polysaccharide in animals.
More about structural
polysaccharides

Cellulose

Major component of plant cell walls.