CARBOHYDRATES
LECTURE OUTLINE
By the end of the lecture, the student
should know:
 The
Importance of carbohydrates.
 The
Definition of Carbohydrates.
 The
Classification of Carbohydrates.
 The
Difference between various
Isomers..
CARBOHYDRATE:
IMPORTANCE
 Most
Abundant Class of
Biomolecules.
 An
Important Macronutrient.
 Performs
important physiological
functions in the body.
 Associated
with Pathological
Conditions (Diabetes Mellitus,
Lactose Intolerance).
DEFINING CARBOHYDRATES
Carbohydrates or Saccharides
(Greek Sakcharon meaning
"Sugar")
 Organic
compounds composed of
Carbon, Hydrogen and oxygen.
 Many
Carbohydrates also contain
Nitrogen and other elements.
Carbohydrates derive their name
from a Misleading Concept
'Hydrates of Carbon’
 Hydrogen
and Oxygen in Carbohydrates
were found to be present in the same
proportion as in water. (2:1).(E.g.
Glucose C6H12O6 or C6 (H2O)6).
 It
is due to this fact that compounds
derived their name “Carbon Hydrate”.
GLUCOSE
H-C=O

H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
This term is not a perfect derivation
as many carbohydrates do not have
the same proportion as water.
Example: DEOXYRIBOSE (C5H10O4)
H-C=O

H-C-H

H-C-OH

H-C-OH

CH2OH
CHEMICAL DEFINITION OF
CARBOHYDRATES
 Polyhydroxyl:
Having more than one
hydroxyl group.
(-OH)
 Functional
Group: It is a specific
group of atoms or bonds which are
part of a larger hydrocarbon
chain.(Provide a specific chemical
behaviour).

For carbohydrates, the functional group is
the carbonyl group which may be either
Aldehyde Group (H-C=O)
Or
Keto Group (C=O)
WHAT IS SIMILAR &
DIFFERENT
IN THESE TWO STRUCTURES?
H-C=O
CH2OH


H-C-OH
C=O
 one hydroxylgroup in both
More than
OH-C-H
OH-C-H


H-C-OH
H-C-OH


CH2OH
CH2OH
WHAT IS COMMON &
DIFFERENT
IN THESE TWO STRUCTURES?
H-C=O
CH2OH


H-C-OH
C=O

Carbonyl
Group inboth But?
OH-C-H
OH-C-H


H-C-OH
H-C-OH


CH2OH
CH2OH
WHAT IS COMMON & DIFFERENT
IN THESE TWO STRUCTURES?
H-C=O
CH2OH


H-C-OH
C=O


Aldehyde
in 1 and Ketone
in 2
OH-C-H
OH-C-H


H-C-OH
H-C-OH


CH2OH
CH2OH
Carbohydrates are
Polyhydroxy Alcohols
with Carbonyl groups
Which May Either Be
Aldehyde (H-C=O) or
Keto (C=O) Groups.
H-C
CH2OH
CAN YOU


O
VISUALIZE
C
H-C-OH
EITHER


ALDEHYDE
OH-C-H
OH-C-H

OR

H-C-OH
KETONE
H-C-OH


GROUP IN
H-C-OH
H-C-OH
THIS


POLYHYDROX
CH2OH
CH2OH
Y ALCOHOL?
NO! BUT
HYDROLYSIS
OF THIS
COMPOUND
YIELDS TWO
COMPOUNDS
WITH
ALDEHYDE
OR KETONE
GROUPS
H-C
CH2OH
HOH 

O
C
H-C-OH


OH-C-H
OH-C-H


H-C-OH
H-C-OH


H-C-OH
H-C-OH


CH2OH
CH2OH
NO! BUT
HYDROLYSIS
OF THIS
COMPOUND
YIELDS TWO
COMPOUNDS
WITH
ALDEHYDE
OR KETONE
GROUPS
H-C =O
CH2OH
HOH 

O
O=C
H-C-OH


OH-C-H
OH-C-H


H-C-OH
H-C-OH


H-C-OH
H-C-OH


CH2OH
CH2OH
MANY POLYHYDROXY ALCOHOLS MAY
NOT HAVE AN ACTIVE ALDEHYDE OR
KETONE GROUP BUT THEY MAY YIELD
THEM ON HYDROLYSIS. THEY
ARE ALSO DESIGNATED AS
CARBOHYDRATES.
THEREFORE, THE COMPLETE
DEFINITION OF CARBOHDRATES IS:
CARBOHYDRATES ARE
POLYHYDROXYL ALCOHOLS
WITH POTENTIALLY ACTIVE
CARBONY GROUPS WHICH MAY
BE EITHER AN ALDEHYDE OR
KETONE GROUP. THEY ALSO
CONTAIN THOSE COMPOUNDS,
WHICH YIELD THEM ON
HYDROLYSIS.
CLASSIFICATION OF CARBOHYDRATES
Carbohydrates are mainly classified
into four different groups:
 Monosachharides
 Disaccharides
 Oligosaccharides
 Polysaccharides
MONOSACCHARIDES
 Monosaccharides are those carbohydrates
which Cannot be Hydrolyzed further into
more simple carbohydrates.
 Thus,
they are the Simplest form of
Carbohydrates.
 Familiar
examples are:
Glucose, Fructose, Ribose & Galactose.
MONOSACCHARIDES ARE FURTHER
CLASSIFIED ON THE BASIS OF:
Aldehyde or Ketone Group:
Aldomonosaccharides (Aldoses).
Ketomonosaccharides (Ketoses).
 Carbon Chain Length.
Trioses.
Tetroses.
Pentoses.
Hexoses.
Heptoses.

CARBONYL GROUP
H-C=O

H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
GLUCOSE
FRUCTOSE-->
CH2OH

C=O

OH-C-H

H-C-OH

H-C-OH

CH2OH
CARBON CHAIN
H-C=O

H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
GLUCOSE
ARABINOSE-->
H-C=O

OH-C-H

H-C-OH

H-C-OH

CH2OH
EXAMPLES OF
MONOSACCHARIDES
NO. OF CARBON
ATOMS
ALDO
KETO
3C TRIOSE
GLYCERALDEHYD
E
DIHYDROXYACET
ONE
4C TETROSE
ERYTHROSE
ERYTHRULOSE
5C PENTOSE
RIBOSE, XYLOSE
RIBULOSE,
XYLULLOSE
6C HEXOSE
GLUCOSE,
GALACTOSE,
MANNOSE
FRUCTOSE
GLYCERALDEHYDE




GLYCERALDEHYDE IS THE SIMPLEST
MONOSACCHARIDE(PARTICULARLY
ALDOSES)
IT CANNOT BE HYDROLYZED FURTHER.
IT IS THE SMALLEST POSSIBLE
STRUCTURE THAT IS A CARBOHYDRATE
CANNOT HAVE LESS THAN 3 CARBON
ATOMS.
GENERAL FORMULA OF
MONOSACCHARIDE: (C•H2O)N
(WHERE N IS ANY NUMBER OF THREE OR
GREATER)
ISOMERISM
 Isomers
are basically molecules that
have the same chemical formula but
they differ in their chemical
structures.
 Asymmetric
Carbon is an important
determinant of Isomerism.
 Asymmetric
Carbon is that Carbon
which is attached with four different
groups.
STRAIGHT CHAIN STRUCTURE OF TYPICAL
MONOSACCHARIDE (GLUCOSE)
Anomeric
Carbon
Epimeric
Carbons
Penultimate
Carbon
Terminal
Alcohol Carbon
THE ASSIGNMENT OF D OR L IS MADE ACCORDING
TO THE ORIENTATION OF THE PENULTIMATE
CARBON
If the Hydroxyl Group is on the right
the molecule is a D sugar,
Otherwise It is an L sugar.
OH
H L-Sugar : D-Sugar
D AND L ISOMERISM PRODUCE MIRROR
IMAGES
EPIMERISM
 Isomers
which differ from each other
only with regard to oh group on a
single asymmetric carbon atom.
OPTICAL ISOMERS
 When
a beam of polarized light is
passed through sugars, they will be
rotated either towards right or left.
 Right
Rotation (dextrorotatory) E.g.
D- Glucose
 Left
Rotation (levorotatory) E.g. DFructose
MONOSACCHARIDE DERIVATIVES OF
BIOLOGICAL IMPORTANCE
 Oxidation
Products (Sugar Acids)
 Reduction
Products (Sugar Alcohols).
 Amino
 Sugar
Sugars.
Phosphates.
OXIDATION PRODUCTS (SUGAR ACIDS)
 When
oxidized under proper conditions,
Aldoses may form three types of acids
(Sugar Acids):

Uronic Acids.

Aldonic acids.

Saccharic Acids.
 Type
of sugar Acid produced depends on
which carbon is oxidized.
H-C=O

H-C-OH

OH-C-H

H-C-OH

H-C-OH

COOH
CH2OH
URONIC ACID
Oxidation Of Aldose
At Primary Alcohol
(Terminal Carbon)
COOH
H-C=O

H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
ALDONIC ACID
Oxidation Of Aldose
At
Carbonyl Carbon
(Aldehyde Group)
COOH
H-C=O

H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
COOH
Saccharic Acid
Oxidation Of Aldose
At Both Aldehyde &
Terminal Carbons
EXAMPLES OF ALDOSES WITH THEIR
CORRESPONDING URONIC ACIDS ARE:
Sugar
Glucose
Uronic Acids
Glucuronic acid,
Iduronic acid
------------- ---------------------Mannose Mannuronic acid
------------- ---------------------Galactose Galacturonic acid
------------- ------------------------
EXAMPLES OF ALDOSES WITH THEIR
CORRESPONDING ALDONIC ACIDS ARE:
Sugar
Glucose
------------Mannose
------------Galactose
-------------
Aldonic Acids
Gluconic acid
---------------------Mannonic acid
---------------------Galactonic acid
------------------------
Amino Sugar:
H-C=O

NH2
H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
Substitution of
Amino Group for a
Hydroxyl Group of a
Sugar Results in the
Formation of an
Amino Sugar.
The Amino Group
is attached to
Carbon 2.
COMMON EXAMPLES OF AMINO SUGARS
(AMINOSACCHARIDES)
 Galactosamine
 Glucosamine
SUGAR ALCOHOLS; REDUCTION PRODUCTS
 Sugar
Alcohols are obtained by reduction
of Monosaccharides (Both Aldoses and
Ketoses) and disaccharides.
 Sugar
alcohols, also known as Polyols,
Polyhydric Alcohols, or Polyalcohols.
SUGAR ALCOHOLS ARE THE HYDROGENATED
FORMS OF THE ALDOSES OR KETOSES
H- C=O + H2

H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
Glucose
CH2OH

H-C-OH

OH-C-H

H-C-OH

H-C-OH

CH2OH
Sorbitol
Sugars with their Corresponding Alcohols
Glyceraldehyde &
Dihydroxyacetone
Glucose
Mannose
Fructose
Galactose
Ribose
Erythrose
Xylose
Lactose
Maltose
Glycerol
Sorbitol (Glucitol)
Mannitol
Sorbitol & Mannitol
Dulcitol
Ribitol
Erythritol
Xylitol
Lactitol
Maltitol
Sugar Phosphates
Phosphate Esters formed by various
Monosaccharides are of Great Importance
in Metabolic Reactions.
Sugar phosphates of biological importance.
Ribose and Deoxyribose in Nucleic Acids
are Phosphate Esters of these
monosaccharides.
Phosphates of Glucose, Fructose and
Glyceraldehyde etc. are important
intermediate compounds in carbohydrate
metabolism of almost all the cells.
DISACCHARIDES
Two
Joined Monosaccharides.
Sucrose: Glucose + Fructose

Maltose: Glucose + Glucose

Lactose: Glucose + Galactose

OLIGOSACCHARIDES
Composed Of:
 Three To Ten
Monosaccharide
Units.
 E.g.
Fructooligosaccharides
POLYSACCHARIDES
Larger Than Ten Monosaccharide
Units.

Can
Reach Many Thousands Of Units.
 Homopolysaccharides.
 Heteropolysaccharides.
HOMOPOLYSACCHARIDES

Similar Types of Monosaccharide
Units.
Starch

Glycogen

Cellulose

HETEROPOLYSACCHARIDES
Different Types of Monosaccharide
Units.

Mucopolysaccharides
(Glycosaminoglycans that contain
galactose and amine sugars)

Agar (Contains various sugars like
Glucose, Galactose)
