Carbohydrates are aldehydes or ketones with multiple hydroxyl groups and are abundant biomolecules that serve various functions, including energy sources and structural components. They are classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides, with examples such as glucose and fructose exhibiting isomerism. Key properties of carbohydrates include their optical activity and reactions such as oxidation and reduction, which result in different sugar derivatives and functional roles in biological systems.

1. SIDRA
MAHMOOD
BS chemistry
MS
biochemistry

3. General Aspects

4.  Carbohydrates are aldehydes or ketone
compounds with multiple hydroxyl groups.
 It is found in relatively in all animals and
plants.
 They are the most abundant biomolecule on
earth.
 But in human they form only 1%of body mass.

5.  Word carbohydrate is derived from the fact
that the first compound of carbohydrate had an
empirical formula C1H2O1.
 This formula was showing hydrogen and
oxygen in same ratio as in water 2:1.
 But now it is known that many carbohydrate
hydrogen and oxygen not in same proportion
as in water. E.g. Deoxyribose whose molecular
formula is C5H10O4.

6.  Carbohydrate is derived from two words
Carbo which means Carbon and Hydrate
which means Water.
 So simply it signifies hydrate of water.

7.  Carbohydrate is define as “the
polyhydroxylated compound with at least
three carbon atom with potentially active
carbonyl group.
 This carbonyl group may be aldehyde or
ketone.
 Carbohydrate contain carbon , hydrogen and
water.
 But some also contain nitrogen, phosphorus, or
sulfur.

8.  Carbohydrate including sugar are called
saccharide.
 “Saccharides "is from Greek word saccharon
which means sugar.

9.  Carbohydrates have a wide range of functions.
The following of them are:
 Source of energy for living beings, e.g. glucose
 Storage form of energy, e.g. glycogen in animal
tissue and starch in plants
 Carbohydrates serve as structural component,
e.g. glycosaminoglycan's in humans,
 Cellulose in plants and chitin in insects
 Non-digestible carbohydrates like cellulose,
serve as dietary fibers.

10.  Constituent of nucleic acids RNA and DNA,
e.g. ribose and deoxyribose sugar.
 Play a role in lubrication, cellular
intercommunication and immunity.
 Carbohydrates are also involved in
detoxification, e.g. glucuronic acid.

11.  Carbohydrate are divided into following
classes
 Monosaccharide
 Disaccharide
 Oligosaccharide
 Polysaccharide
 Derived carbohydrate
 Lets explain them one by one

12.  These include simple sugar which consist of a
single polyhydroxylated aldehyde or ketone
units.
 They cannot be further hydrolyzed into simple
carbohydrate as they are the simplest form of
the carbohydrate.
 with few exception it has the empirical formula
(CH2O)n where n=3 or larger number

13.  When aldehyde is present in monosaccharide
then it always occur at the end of carbon chain.
 But when ketone is present then it never occur
at the end but at some other place.
 For example glucose contain aldehyde while
fructose contain ketone group.
 The most abundant monosaccharide in nature
is six carbon sugar D-glucose.

16.  May be subdivided into two groups as follows:
 Depending upon the number of carbon atom
they posses
 For example ;trioses, tortoises , pentose's ,
hexoses , heptodes.
 Depending upon the functional aldehyde
(CHO) or ketone (C=O) group present:
 Aldoses and ketoses

17.  Classification of monosaccharide's based on the
number of carbon and the type of functional
group present examples are given in table;

18.  It is given in the table;

19.  The compounds possessing identical molecular
formula but different structures are referred to
as isomers.
 The phenomenon of existence of isomers is
called isomerism.
 (Greek “isos” means equal, “meros” means
parts).

20.  The five types of isomerism exhibited by sugar
are as follows:
1. Ketose-aldose isomerism
2. D and L isomerism
3. Optical isomerism
4. Epimerism
5. Anomerism

21.  Glucose and fructose are isomers of each other
having the same chemical (molecular) formula
C6H12O6.
 But they differ in structural formula with
respect to their functional groups.
 There is a keto group in position two of
fructose and an aldehyde group in position one
of glucose.
 This type of isomerism is known as ketose-
aldose isomerism.

23.  D and L isomerism depends on the orientation
of the H and OH groups around the
asymmetric carbon atom adjacent to the
terminal primary alcohol carbon,
 e.g. carbon atom number 5 in glucose
determines whether the sugar belongs to D or
L isomer.
 D stand for dextrorotatory designated as (+)
 L stand for levorotatory designated as (-)

24.  When OH group on this carbon atom is on the
right, it belongs to D-series, when it is on the
left; it is the member of the L-series.
 The structures of D and L-glucose based on the
reference monosaccharide, D and L
glyceraldehyde, a three carbon sugar.
 • D and L isomers are mirror images of each
other. These two forms are called enantiomers.

26.  These are the pair of stereoisomer that are the
mirror image of each other in regard to
asymmetric carbon atom present in the
molecule.
 For example D and L form of glucose isomer.
 The D and L monosaccharide are metabolized
by a specific enzymes.
 The D enzymes will not work on L enzymes
and vice versa.
 In mammals mostly D-type of monosaccharide
are present.

27.  The presence of asymmetric carbon atoms exhibits
optical activity on the compound.
 Optical activity is the capacity of a substance to rotate
the plane polarized light passing through it.
 When a beam of plane-polarized light is passed
through a solution of an optical isomer, it will be
rotated either to the right and is said to be
dextrorotatory (d) or (+) or to the left and is said to be,
levorotatory (l) or (-).
 • When equal amount of D and L isomers are present,
the resulting mixture has no optical activity.
 Since the activity of each isomer cancel one another,
such a mixture is said to be a racemic or dl mixture

28.  Naturally occurring glucose is dextro while
fructose is levorotatory.
Optical activity in monosaccharide:
 Light being an electromagnetic radiation vibrates in
plane which are perpendicular to its direction od
propagation.
 If light is made to pass through a certain media then
the light leaving these media possess only one plane of
oscillation.
 In other words light becomes polarized in one plane
and such a light is called plane-polarized light.

29.  Plane-polarized light is measured in a Polari
meter or Polaris cope.
 Principle of instrument:
 A beam of light of known wave length is passed
through a nicol prism.
 This prism is acting as the polarizer converts it into a
plane polarized light.
 This beam is then passes through a solution of a
chemical substance contained in a glass tube of known
length.
 A 2nd nicol prism acts as analyzer it can be rotated to
find out degree of rotation.

30.  When two monosaccharide's differ from each other
in their configuration around a single asymmetric
carbon (other than anomeric carbon) atom, they
are referred to as epimers of each other.
 For example, galactose and mannose are two
epimers of glucose.
 They differ from glucose in the configuration of
groups (H and OH) around C-4 and C-2
respectively.
 Galactose and mannose are not epimers of each
other as they differ in configuration at two
asymmetric carbon atoms around C-2 and C-4.

32. α and β Anomerism:
 The predominant form of glucose and fructose in a solution are
not an open chain. Rather, the open chain form of this sugar in
solution cyclize into rings.
 An additional asymmetric center is created when glucose cyclizes.
 Carbon-1 of glucose in the open chain form becomes an
asymmetric carbon in the ring form and two ring structures can be
formed.
 These are:
• a-D-glucose
• b-D-glucose
 The designation a means that the hydroxyl group attached to C-1
is below the plane of the ring, b means that it is above the plane of
the ring. The C-1 carbon is called the anomeric carbon atom and
so, a and b forms are anomers.

34.  Some of the important chemical properties of
monosaccharide's are:
 1. Action of strong acids: Furfural formation
 2. Action of alkalis: Enolization
 3. Oxidation: Sugar acid formation
 4. Reduction: Sugar alcohol formation
 5. Action of phenyl hydrazine: Osazone
formation.

35.  On heating a sugar with mineral acids (H2SO4
or HCl), the sugar loses water and forms
furfural derivatives.
 These may condense with a-naphthol, thymol,
or resorcinol to produce
 colored complexes. This is the basis of the:
 • Molisch’s test
 • Seliwanoff’s test
 • Bial’s test
 • Tollen’s-phloroglucinol-HCl test.

36.  On treatment with dilute aqueous alkalis, both
aldoses and ketoses are changed to enediols.
 Enediol is the enol form of sugar because two OH
groups are attached to the double bonded carbon.
 • Enediols are good reducing agents and form
basis of the
 Benedict’s test and Fehling’s test.
 • Thus, alkali enolizes the sugar and thereby
causes them to be strong reducing agents.
 • Through the formation of a common 1, 2-enediol,
glucose, fructose, and mannose may isomerize into
each other in a dilute alkaline solution

38.  When aldoses oxidize under proper conditions they
may form:
 –– Aldonic acid
 –– Saccharic acids
 –– Uronic acid.
 • Oxidation of an aldose with hypobromous acid
(HOBr), which acts as an oxidizing agent gives aldonic
acid.
 Thus, glucose is oxidized to gluconic acid.
 • Oxidation of aldoses with nitric acid under proper
conditions converts both aldehyde and terminal
primary alcohol groups to carboxyl groups, forming
saccharic acid.

39.  Both aldoses and ketoses may be reduced by
enzymes or non-enzymatically to the
corresponding polyhydroxy alcohols.
 Manitol, the sugar alcohol derived from
mannose, is frequently used medically as an
osmotic diuretic to reduce cerebral edema.
 • Sorbitol, the sugar alcohol derived from
glucose, often accumulates in the lenses of
diabetics and produces cataracts.

40.  Osazones are yellow or orange crystalline derivatives of reducing
sugars with phenylhydrazine and have a characteristic crystal
structure, which can be used for identification and
characterization of different sugars having closely similar
properties (like maltose and lactose).
 Osazone formed from glucose, mannose, and fructose are identical
because these are identical in the lower four carbon atoms.
 The osazone crystals of glucose and of the reducing disaccharides,
lactose and maltose differ in forms
 –– Glucosazone is needle shaped
 –– Lactosazone is powder puff or tennis ball shaped
 –– Maltosazone is sunflower shaped.
 Non-reducing sugars like the disaccharide sucrose cannot form
osazone due to the absence of a free carbonyl (CHO or C = O)
group in them.

41.  Some important sugar derivatives of
monosaccharide's are:
 • Phosphoric acid ester of monosaccharide's
 • Amino sugar
 • Deoxy sugars
 • Sugar acids
 • Sugar alcohols
 • Neuraminic acid
 • Sialic acid.

42.  Phosphorylation of sugar within cells is
essential to
 prevent the diffusion of the sugar out of the
cell.
 • Nucleic acids (RNA and DNA) of cell nuclei
also contain sugar phosphates of ribose and
deoxyribose.

44.  • Amino sugars are components of glycolipid
(ganglioside), glycoprotein, and proteoglycans
(glycosaminoglycan's).
 • Several antibiotics, e.g. erythromycin,
carbomycin contain amino sugar.

45. Deoxy sugars possess a hydrogen atom in place of
one of
 their hydroxy groups e.g. 2-deoxyribose found
in nucleic acid DNA.

46. Sugar acids are produced by oxidation of the
monosaccharide's,
 for example:
 • Ascorbic acid or vitamin C (not synthesized by
human
 beings) is required for the synthesis of collagen. It
acts
 as water soluble antioxidant.
 • Glucuronic acid (uronic acid) (see properties of
monosaccharide:
 oxidation).

47. Neuraminic acid is a nine carbon sugar derived
from mannosamine (an epimer of glucosamine)
and pyruvate.
 Mannosamine + Pyruvate ————>
Neuraminic acid

48. Sialic acids are constituents of both glycoproteins
and glycolipids (ganglioside).

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