This document discusses carbohydrates including monosaccharides, disaccharides, and polysaccharides. It explains that monosaccharides have formulas of C5H10O5 or C6H12O6 and exist as pentoses or hexoses like glucose. Monosaccharides can form ring structures and optical isomers. Disaccharides like sucrose form from monosaccharide condensation, while polysaccharides like starch are made of many monosaccharide units and provide structure or energy storage. Polysaccharides serve important functions in the body including energy provision, energy storage as glycogen, and as dietary fiber.

1. Carbohydrates

2. Monosaccharides
• All monosaccharides have the empirical
formula CH2O.
• They contain a carbonyl group in addition to
this and at least two –OH groups.
• They have between 3 and 6 carbon atoms.

3. Types of Monosaccharides
• Monosaccharides with the formula C5H10O5
are generally known as pentoses (ribose is an
example of this).
• Monosaccharides with the formula C6H12O6
are known as hexoses (glucose is an example
of this).

4. Monosaccaharides Structures
• Many structural isomers are possible.
• In addition several carbon atoms are chiral
(asymmetric) and give rise to optical
isomerism.
• Open chain structures and ring structures are
also possible.

5. • The form of natural glucose
is known as D-glucose.
• The picture on the left is of
a straight chain formation
of D-glucose.

6. Ring Structure of D-glucose
The ring structure of D-glucose can exist in two separate
crystalline forms known as α-D-glucose and β-D-glucose.
The only difference is the the –OH group on the first
carbon atom is inverted.

7. Monosaccharides cont.
• Six-membered ring monosaccharides are
known as pyranoses.
• Hexoses can also have a furanose structure
where they have a five-membered ring
containing an oxygen atom.

8. Polysaccharides
• Monosaccharides can undergo condensation
reactions to form disaccharides and eventually
polysaccharides.

9. Sucrose
• Sucrose is a disaccharides formed from the
condensation of α-D-glucose in the pyranose
form and β-D-frutose in the furanose form.
• The bond formed is known as a glycosidic link.

10. Sucrose continued
• In the case of sucrose the link is between the
C-1 atom of glucose in the α-configuration and
the C-2 atom of frutose. The links is known as
a β-1,2 bond.

11. • Maltose, another disaccharide is formed from
two glucose molecules condensing to form an
α-1,4 bond.

12. • Lactose is a disaccharide in which the β-D-
galactose is linked at the C-1 atom to the C-4
atom of β-D-glucose. This is called a β-1,4
bond.

13. Starch
• Starch is one of the most important
polysaccharides.
• Starch exists in two forms: amylose, which is
water soluble and amylopectin, which is
insoluble in water.

14. Amylose
• Amylose is a straight chain polymer of α-D-
glucose units with α-1,4 bonds.

15. Amylopectin
• Amylopectin also contains α-D-glucose units
but it has a branched structure with both α-
1,4 and α-1,6 bonds.

16. • Most plants use starch as a store of carbohydrates
and their energy.
• Cellulose, a polymer of β-D-glucose contains β-1,4
links. Cellulose, together with lignin, provides the
structure to the cell wall of green plants.
• most animals, including all mammals, do not have
the enzyme cellulase so are unable to digest cellulose
or other dietary fiber polysaccharides.

17. Functions of Polysaccharides in the
Body
• To provide energy
– Food such as
bread, biscuits, cake, potatoes, pasta, and cereals
are all high in carbohydrates.
• To store energy
– Starch is stored in the livers of animals in the form
of glycogen. Glycogen has almost the same
chemical structure as amylopectin.

18. (cont.)
• As precursors
– For other important biological molecules they are
components of nucleic acids and thus play an
important role in the biosynthesis of proteins.
• As dietary fiber
– Dietary fiber is mainly plant material that is not
hydrolysed by enzymes secreted by the human
digestive tract by may be digested by microflora in the
gut.
– It may be helpful in preventing conditions such as
diverticulosis, irritable bowel
syndrome, obesity, Crohn’s disease, haemerrhoids and
diabetes mellitus.