Carbohydrates are polyhydroxyaldehydes or polyhydroxyketones that can be hydrolyzed into monosaccharides like glucose or fructose. They include monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Glucose is a key monosaccharide that circulates in the blood and is an important energy source for cells. Starch and cellulose are important polysaccharides used for energy storage in plants and structural support in plant cell walls. Carbohydrates serve critical roles as energy sources and structural components in both plants and animals.

1. Carbohydrates
Archana Soni
archi22ss@gmail.com

2. Carbohydrates – polyhydroxyaldehydes or polyhydroxy-
ketones of formula (CH2O)n, or compounds that can be
hydrolyzed to them. (aka sugars or saccharides)
Monosaccharides – carbohydrates that cannot be hydrolyzed
to simpler carbohydrates; eg. Glucose or fructose.
Disaccharides – carbohydrates that can be hydrolyzed into
two monosaccharide units; eg. Sucrose, which is hydrolyzed
into glucose and fructose.
Oligosaccharides – carbohydrates that can be hydrolyzed into
a few monosaccharide units.
Polysaccharides – carbohydrates that are are polymeric
sugars; eg Starch or cellulose.

3. Aldose – polyhydroxyaldehyde, eg glucose
Ketose – polyhydroxyketone, eg fructose
Triose, tetrose, pentose, hexose, etc. – carbohydrates that
contain three, four, five, six, etc. carbons per molecule
(usually five or six); eg. Aldohexose, ketopentose, etc.

4. Reducing sugar – a carbohydrate that is oxidized by Tollen’s,
Fehling’s or Benedict’s solution.
Tollen’s: Ag+
 Ag (silver mirror)
Fehling’s or Benedict’s: Cu3+
(blue)  Cu2+
(red ppt)
These are reactions of aldehydes and alpha-hydroxyketones.
All monosaccharides (both aldoses and ketoses) and most*
disaccharides are reducing sugars.
*
Sucrose (table sugar), a disaccharide, is not a reducing sugar.

5. Glucose (a monosaccharide)
Plants:
photosynthesis
chlorophyll
6 CO2 + 6 H2O C6H12O6 + 6 O2
sunlight (+)-glucose
(+)-glucose starch or cellulose
respiration
C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy

6. Animals
plant starch (+)-glucose
(+)-glucose glycogen
glycogen (+)-glucose
(+)-glucose fats or aminoacids
respiration
(+)-glucose + 6 O2 6 CO2 + 6 H2O + energy

7. OH
CHO
H
CH2OH
H
CHO
HO
CH2OH
D-(+)-glyceraldehyde L-(-)-glyceraldehyde
glyceraldehyde
an aldotriose
CH2CHCH O
OH OH
*
D & L are used to relate configuration of the chiral center
most removed from the reducing group ( C=O ). If the -OH
is on the right in the Fischer projection, then it is D, if the -OH
is on the left, then it is L

8. CHO
H OH
CH2OH
H OH
aldotetroses
CH2CHCHCH O
OH OHOH
* *
CHO
HO H
CH2OH
HO H
CHO
H OH
CH2OH
HO H
CHO
HO H
CH2OH
H OH
D-erythrose L-erythrose
L-threose D-threose

9. (+)-glucose? An aldohexose
Emil Fischer (1902)
Four chiral centers, 24
= 16 stereoisomers
CHO
CH2OH
OH?
CH2CHCHCHCHCH O
OH OHOHOHOH
* * * *

10. CHO
OHH
OHH
OHH
OHH
CH2OH
CHO
HHO
OHH
OHH
OHH
CH2OH
CHO
OHH
HHO
OHH
OHH
CH2OH
CHO
HHO
HHO
OHH
OHH
CH2OH
CHO
OHH
OHH
HHO
OHH
CH2OH
CHO
HHO
OHH
HHO
OHH
CH2OH
CHO
OHH
HHO
HHO
OHH
CH2OH
CHO
HHO
HHO
HHO
OHH
CH2OH
CHO
HO H
HO H
HO H
HO H
CH2OH
CHO
H OH
HO H
HO H
HO H
CH2OH
CHO
HO H
H OH
HO H
HO H
CH2OH
CHO
H OH
H OH
HO H
HO H
CH2OH
CHO
HO H
HO H
H OH
HO H
CH2OH
CHO
H OH
HO H
H OH
HO H
CH2OH
CHO
HO H
H OH
H OH
HO H
CH2OH
CHO
H OH
H OH
H OH
HO H
CH2OH

11. Ruff degradation – a series of reactions that removes the
reducing carbon ( C=O ) from a sugar and decreases the
number of chiral centers by one; used to relate configuration.
CHO
H OH
CH2OH
H OH
CO2H
H OH
CH2OH
H OH
Br2
H2O
CO2
H OH
CH2OH
H OH
Ca2+
H2O2
Fe3
+
CHO
CH2OH
H OH
D-(+)-glyceraldehyde

12. Kiliani-Fischer synthesis. A series of reactions that extends the
carbon chain in a carbohydrate by one carbon and one chiral
center.
CHO
H OH
CH2OH
HCN
C
H OH
CH2OH
H OH
C
HO H
CH2OH
H OH+
N N
H+,H2O
COOH
H OH
CH2OH
H OH
COOH
HO H
CH2OH
H OH
diastereomers
separable
C
H OH
H2C
H OH
O
O
lactone
Na(Hg)
CHO
H OH
CH2OH
H OH
-H2O

13. Epimers – stereoisomers that differ only in configuration about
one chiral center.
CHO
OHH
HHO
OHH
OHH
CH2OH
D-glucose
CHO
HHO
HHO
OHH
OHH
CH2OH
D-mannose
epimers

14. CHO
OHH
HHO
OHH
OHH
CH2OH
(+)-glucose
Exists only in solution. There are two
solids:
α-glucose m 146o
[α] = +112.2
β-glucose m 150o
[α] = +17.5
In water each mutarotates to an
equilibrium with [α] = +52.7
(63.6% β / 36.4% α)

15. CHO
OHH
HHO
OHH
OHH
CH2OH
O
H
HO
H
HO
H
OH
OHH
H
OH
O
H
HO
H
HO
H
H
OHH
OH
OH
alpha-(+)-glucose beta-(+)-glucose
OH
OH
OH
H
H
OHH
OH
CH2OH
OH
OH
H
OH
H
OHH
OH
CH2OH

16. R
C
H
O
+ R'OH R C H
OH
OR'
R C H
OR'
OR'
hemiacetal
geminal
ether/alcohol
reducing!
acetal
geminal
diether
non-reducing!
Addition of alcohols to aldehydes/ketones:

17. CHO
OHH
HHO
OHH
OHH
CH2OH
O
H
HO
H
HO
H
OH
OHH
H
OH
O
H
HO
H
HO
H
H
OHH
OH
OH
nucleophilic addition of -OH on carbon 5 to the aldehyde functional group
CHO
OHH
HHO
OHH
OHH
CH2OH
CH
OHH
HHO
OHH
HHOH2C
OH
O
H
HO
H
HO
H
OH
OHH
H
OH
O
O
H
HO
H
HO
H
H
OHH
OH
OH
α
β
rotate C-5 OH to rear

18. O
H
HO
H
HO
H
H
OHH
OH
OH
O
H
HO
H
HO
H
OH
OHH
H
OH
hemiacetal
4H-Pyran
O
D-glucopyranoses
alpha beta

19. OH
H
H
H OH
HO H
O
H
HOHO
H
OH
H
H OH
HO H
O
H
HOHO
O
furan
alpha furanose form beta furanose form
D-glucofuranoses

20. O
H
HO
H
HO
H
H
OHH
OH
OH
O
H
HO
H
HO
H
OH
OHH
H
OH
alpha beta
anomers - epimers at C-1
chair conformations - alpha has one group axial
beta has all groups equatorial
mutarotation in solution to 63.6% beta/36.4% alpha

21. CH2OH
O
HHO
OHH
OHH
CH2OH
D-fructose
CH2OH
OH
H
CH2OH
OH H
H OH
O
beta-D-fructofuranose
OH
CH2OH
H
CH2OH
OH H
H OH
O
alpha-D-fructofuranose

22. O
H
HO
H
HO
H
H
OHH
OH
OH
CH3OH
HCl
O
H
HO
H
HO
H
H
OHH
OCH3
OH
acetal
(glucoside - glucose acetal)
non-reducing, does not muta-
rotate
methyl beta-D-glucoside

23. Disaccharides:
(+)-maltose “malt sugar”
two glucose units (alpha)
(+)-cellobiose
two glucose units (beta)
(+)-lactose “milk sugar”
galactose & glucose
(+)-sucrose “table sugar”
glucose & fructose

24. (+)-maltose
O
H
H
HO
H
H
OHH
OH
OH
O
H
HO
H
HO
H
OHH
H
OH
O
two glucose units
alpha C-1 to C-4
reducing sugar
O
H
HO
H
HO
H
H
OHH
OH
O
H
O
H
HO
H
H
OHH
OH
OH
(+)-cellobiose
two glucose units
beta C-1 to C-4
reducing sugar

25. O
H
HO
H
HO
H
OHH
H
OH
glucose alpha C-1
to beta C1 fructose
O
HO
H
H
HO
H
H
OHH
OH
O
H
O
H
HO
H
H
OHH
OH
OH galactose beta C-1
to C-4 glucose
reducing sugar(+)-lactose
O
O
CH2OH
CH2OH
H
H
OH
HO
H
(+)-sucrose
acetal
non-reducing

26. Polysaccharides
starch
cellulose
Starch 20% amylose (water soluble)
80% amylopectin (water insoluble)
amylose + H2O  (+)-maltose
(+)-maltose + H2O  (+)-glucose
starch is a poly glucose (alpha-glucoside to C-4)
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O

27. O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
CH2
O
Amylopectin + H2O  (+)-maltose
(+)-maltose + H2O  (+)-glucose
Also a polyglucose, but branched every 20-25 units:

28. Cellulose is a polyglucose with a beta-linkage:
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O

29. Biological significance of carbohydrates in living organisms is as
follows:
Carbohydrates are energy stores of animals and plants.
Carbohydrates are immediate source of energy while lipids are long-term source
of energy.
Glucose is a free sugar which circulates in blood and is an important substance
for normal cell functioning.
Regulation of glucose metabolism is vital for survival. Carbohydrates make up
most of the plant of about 60-80% of its dry mass.
In plants they are used as energy source and for storage in the form of starch.
Cellulose which is a polysaccharide is an important structural component in the
cell wall of plants.
Sucrose, a disaccharide is a product of photosynthesis and is transported
internally.
Carbohydrates are an important component of diet in animals.
Carbohydrates are main source of energy and are essential to all animal life.
Carbohydrates act as fuel to physical body parts on daily basis.

30. Within the body carbohydrates
have six major functions:
They provide energy and regulate
blood glucose.
Help in breakdown of fatty acids
and prevents ketosis.
Aid in biological recognition
processes.
They minimize the use of proteins
for energy.
They also act as flavor and
sweeteners.