Carbohydrates are biomolecules composed of carbon, hydrogen, and oxygen. They are classified as monosaccharides, oligosaccharides, or polysaccharides depending on the number of monomer units present. Monosaccharides include simple sugars like glucose and fructose. Disaccharides are formed from two monosaccharides joined by a glycosidic bond, examples being sucrose and lactose. Polysaccharides are polymers of monosaccharides and include starch, glycogen, and cellulose. Carbohydrates serve important functions as energy sources, structural components of cells and organisms, and precursors for other biomolecules.

1. CARBHOHYDRATES
Dr. P. SUGANYA
ASSISTANT PROFESSOR
Department of Biotechnology
SRI KALISWARI COLLEGE (Autonomous),Sivakasi

2. Definition
• Carbohydrates are most abundant biomolecules in the
nature
• Carbohydrates are molecules that contain carbon,
hydrogen, and oxygen.
• There are twice as many hydrogen atoms as carbon or
oxygen atoms.
• The general formula for a carbohydrate can be written
as Cx(H2O)y.
• They act as the source of energy (e.g. glucose), as a
store of energy (e.g. starch and glycogen) and as
structural units (e.g. cellulose in plants and chitins in
insects).

3. Functions
• Carbohydrates are involved in various functions:
• They also act as precursor for many organic compounds.
• It also involved in structural components of many
organisms.
• It also involves in immediate source of energy demands
of the body by serving as the storage form of energy
(glycogen).
• They also involved in the structural and cellular functions
of cell such as- fertilization, cell growth and adhesion.

4. Classifications

5. • Carbohydrates are commonly referred to as
a saccharides (greek: sakcharon means sugar).
• Carbohydrates are classified into three major groups
depending upon whether these undergo hydrolysis and if
so on then the number of products formed by them.
o Monosaccharides
o Oligosaccharides
o Polysaccharides

7. • Most carbohydrates are polymers.
• Polymers are large, complex molecules composed of
long chains of monomers.
• Monomers are small, basic molecular units.
• Carbohydrates can be divided into three groups:
monosaccharides, disaccharides, and polysaccharides.

8. Monosaccharides – Structure,
Properties, and Examples

10. • Greek: mono means one.
• Monosaccharides are simple sugars in which there are
one oxygen atom and two hydrogen atoms for each
carbon atom present in the molecule.
• They have general formula as (CH2O)n.
• Monosaccharides are reducing sugars.
• The test for reducing sugar is called Benedict’s test.
• They are sugars, which taste sweet, are soluble in water
and are insoluble in non-polar solvents.
• They exist in straight chains or in the ring or cyclic
forms.

11. • They are classified according to the number of carbon
atoms in each molecule as trioses (3C), tetroses (4C),
pentoses (5C), hexoses (6C), heptoses (7) and so on.
• The names of all sugars end with -ose.
• Examples: Glyceraldehyde (triose), Erythrose (tetrose),
Ribose (pentose), Glucose (hexose), Fructose (hexose),
Galactose (hexose), Sedoheptulose (heptose), etc.
• They are used as a source of energy in respiration.
• They are important building blocks for large molecules.
•

12. Disaccharides – Structure,
Properties, and Examples

13. • Disaccharides are made up of two monosaccharides
joined together by a condensation reaction.
• The condensation reaction is the joining of two
molecules with the formation of a new chemical bond
and a water molecule is released when the bond is
formed.
• A glycosidic bond is formed between two
monosaccharides. If carbon 1 on one monosaccharide
joins to carbon 4 on another monosaccharide, it is called
a 1,4-glycosidic bond.
• Disaccharides are the most common, among
oligosaccharides.
• It consists of two monosaccharides units which is held
together by glycosidic bond.
• It is crystalline, soluble in water and sweet in taste.

15. • Examples: Maltose is formed from two α-glucose
molecules joined together by a glycosidic
bond. Sucrose is formed from a condensation reaction
between a glucose molecule and a fructose
molecule. Lactose is formed from glucose and a
galactose molecule.
• Sucrose is a non-reducing sugar.
• Disaccharides can be split apart into two
monosaccharides by breaking the glycosidic bond by
adding water molecules, which is known as hydrolysis
reaction. The water provides a hydroxyl group (-OH)
and hydrogen (-H), which helps the glycosidic bond to
break.
• Sucrose is the transport sugar and Lactose is the sugar
found in milk which an important constituent of the diet of
young mammals.

16. Polysaccharides –
Structure, Properties, and
Examples
• Polysaccharides are polymers formed by combining many
monosaccharide molecules (more than two) by
condensation reactions.
• Molecules with 3-10 sugar units are known
as oligosaccharides while molecules containing 11 or more
monosaccharides are true polysaccharides.
• Polysaccharides do not taste sweet.
• Because their molecules are so enormous, the majority of
polysaccharides do not dissolve in water.
• Polysaccharides made solely from one kind of
monosaccharides are
called homopolysaccharides (Starch) while those made of
more than one monomer are
called heteropolysaccharides (Hyaluronic acid).

17. • Greek: poly means many.
• They are generally polymers of monosaccharide units
with high molecular weight.
• They are tasteless and most often form colloids with
water.
• It is linear as well as branched polymer.
• It is of two types:
o Homopolysaccharides: it yields only a single type of monosaccharide on
hydrolysis.
o Heteropolysaccharides: it yields a mixture of a few monosaccharides or their
derivatives on hydrolysis

19. • Starch is made up of long chains of α-glucose (Amylose
and Amylopectin). Glycogen is made of α-glucose linked
together by glycosidic bonds. Cellulose is also made of
many β-glucose molecules linked by glycosidic bonds
between carbon 1 and carbon 4.
• Starch is the main energy storage materials in
plants. Glycogen is the main energy storage materials in
animals. Cellulose is the major component of cell walls
in plants.
• The test for starch is called an Iodine test.

21. References
• CGP. 2015. A-Level Biology Exam Board: AQA.
Complete Revision and Practice. Original material by
Richard Parsons.
• Glenn Toole and Susan Toole. 2015. AQA Biology for A-
Level. 2nd Edition. Oxford University Press.
• https://microbenotes.com/carbohydrates/