Carbohydrates are made of carbon, hydrogen, and oxygen. Monosaccharides like glucose are simple sugars that provide energy. Glucose can exist as an open chain or ring structure. Disaccharides like sucrose are formed by joining two monosaccharides. Polysaccharides such as starch, glycogen, and cellulose are made of many monosaccharide units and function as energy stores. Starch is made of amylose and amylopectin. Cellulose is an unbranched polymer of glucose units linked by beta bonds that provides structure to plant cells.

1. Carbohydrates
Saccharides

2. The basic formula is:
Cx
(H2
0)y
or (CH2
O)n
All carbohydrates are Aldehydes or ketones
Aldehydes oxidise easily and make good reducing
agents.
They have many –OH groups

3. MONOSACCHARIDES
These are simple sugars
They are used to release energy or as monomers
in larger molecules.
They are sweet
They are soluble in water
e.g. glucose: C6
H12
O6

4. TEST FOR REDUCING SUGARS
Reducing sugars are able to
Reduce Copper II Sulfate to Copper I oxide
(Blue, soluble) (red,
insoluble)
Benedict’s solution is made
using Copper II sulfate
which is a blue solution

5. Benedict’s test

6. This solution tested
positive for
reducing sugars
This solution is
negative for reducing
sugars

7. Ring Structures
Glucose can exist as a chain or fold around to form a 6
sided ring structure

8. Note the
carbons are
numbered 1-6
Carbon 6 is
outside of the
ring attached to
carbon 5

9. Note carbon 6 is
above the ring
Some OH and some H
groups are below the
ring
Carbon 1 is
asymmetrical
It has 4 different groups
attached
H
OH
O and
C

10. In nature glucose exists in two forms
In beta glucose the OH is above the
ring structure
Alpha glucose Beta glucose

11. ALPHA GLUCOSE BETA GLUCOSE

12. Disaccharides
These are formed by condensation – removing water
These are both molecules of -∝ glucose
A bond is formed by removing OH from carbon 1 on one
molecule
And an H on carbon 4 of the adjacent molecule

13. This is an
∝-1.4 glycosidic bond
Water is made
Maltose is the disaccharide formed

14. Lactose a disaccharide formed by joining
Galactose and Glucose

15. Sucrose
This is a disaccharide that is a non-reducing
sugar

16. Test for Non-Reducing Sugar
1. Carry out Benedict's test: negative result so
no reducing sugars
2. Hydrolyse the unknown to split the sugar into
monosaccharides:

Add hydrochloric acid

Heat in a water bath

neutralise using hydrogen carbonate
3. Repeat Benedict's test
If it goes Brick red this time there is non-reducing
sugar present

17. POLYSACCHARIDES
e.g. starch, glycogen, cellulose
Polysaccharides are food and energy stores
They are large and insoluble so do not affect
water potential or influence chemistry of cell
They can fold into compact shapes
Polysaccharides are easily converted by
hydrolysis to sugars when required

18. STARCH
Starch is a polymer of α-glucose
This is the main storage compound in plants
Has two components:
Amylose and
amylopectin

19. AMYLOSE
Straight chain of -glucose molecules joined by 1,4α α
glycosidic bonds
Helically coiled making it compact.
200-1500 residues

20. AMYLOPECTIN
Makes up about 70% starch
Many more residues, 2000-200-000
Some residues joined with 1,4 glycosidic bonds andα
helically coiled
Some branched with 1,6 glycosidic bondsα

21. Alpha 1,6, glycosidic bond
Alpha 1,4 glycosidic bond

22. GLYCOGEN
Glycogen is the storage polysaccharide in animal
cells (particularly in liver and muscle cells) and
many fungi
Similar in structure to amylopectin but has more
branching and is larger

24. CELLULOSE
50% of Carbon in a plant is cellulose
It is the most abundant organic molecule on earth
Cellulose is an unbranched polymer of 2000-
3000 β-glucose molecules
Held by β 1,4-glycosidic bonds

25. Beta glucose
Cannot form glycosidic bonds like this
The OH of the first molecule is above
the ring structure

26. If one molecule flips through 180
degrees then the OH groups align on
carbon 1 and 4 and condensation can
occur

27. Beta 1,4,glycosidic bond

28. The next glucose molecule will need to be the same as
the first one
This time the beta-1,4 glycosidic bond is formed below
the ring structure

29. And so on…
Cellulose is a long, straight molecule

30. Cellulose molecules lie next to each other and are
held together by weak hydrogen bonds
There are many of these bonds which makes the
overall structure strong

31. These molecules are bundled into microfibrils which are
in turn bundled into cellulose fibres
These fibres have a high tensile strength