3. • Carbohydrates are the most abundant organic
molecule in nature.
• They are also called saccharides.
• The general molecular formula Cn(H2O)n
• For example glucose – C6H12O6
4. DEFINITION
• CARBOHYDRATES ARE DEFINED AS
POLYHYDROXY ALDEHYDES OR KETONES
OR COMPOUNDS WHICH PRODUCE THESE
DERIVATIVES ON HYDROLYSIS
6. • Main source of energy in the body(brain cells
and RBCs are dependent on carbohydrates),
• Energy production from carbohydrates will be
4 kilo calories /gram
• They are the precursors for many organic
compounds(fats and amino acids)
7. • Carbohydrates (glycoproteins and glycolipids)
participate in the structure of cell membrane
• Storage form of energy(starch and glycogen)
8. • They are the structural components of many
organisms.
• These include the fiber(cellulose) of plants,
exoskeleton of some insects and the cell wall of
microorganisms
11. Monosaccharides are the simple sugars.
They cannot be hydrolyzed in to simple forms
Monosaccharides are subdivided in to different
group as follows.
12. ALDOSES AND KETOSES
• Aldoses ;when the functional group in monosaccharides is an
aldehyde group(CHO), they are known as aldoses eg. Glucose
• Ketoses; when the functional group in monosaccharides is a
keto group (C=O) , they are ketoses, eg. fructose
13. • Based on the number of carbon atom ,monosaccharides are
regarded as trioses(3C), tetroses(4C), pentoses(5C),
hexoses(6C) etc
• These term along with functional groups are used while
naming monosaccharides
• Eg. Glucose is an aldohexose while fructose is a ketohexose
16. OLIGOSACCAHRIDES
• Oligosaccahrides contain 2-10 monosaccahride
molecules joined together by a bond called
GLYCOSIDIC BOND which on hydrolysis gives
two to ten molecules of simple sugars.
• Based on the number of monosaccharides units
present, the oligosaccharides are subdivided in to
DISACCHARIDES and TRISACCHARIDES
17. EXAMPLES FOR DISACCAHRIDES
• Sucrose- glucose and fructose
• Lactose –glucose and galactose
• Maltose –glucose and glucose
Trisaccharides–
• Raffinose-galactose+ fructose+ glucose
• Maltotriose- 3 glucose units
18. POLYSACCHARIDES
• Polymers of monosaccharides ,more than 10
monosaccharides are combined to form
polysaccharides. They are also called glycans.
• They are of 2 types
• Homopolysaccharides(homoglycans)
• Heteropolysaccharides(hetereoglycans)
19. • Homopolysaccharides (homoglycans)-
composed of same type of monosaccharides
• They are named based on the nature of
monosaccharide unit
• Thus Glucans are polymers of glucose
• Fructosans are polymers of fructose
24. PROPERTIES OF MONOSACCHARIDES
• Stereoisomerism
• Assymetric carbon
• D and L isomers
• Optical activity
• Racemic mixtures
• Epimerism
• Anomerism
25. STEREOISOMERISM
• Important character of monosaccharides
• Stereoisomers are Compounds having same
structural formula but differ in their spatial
configuration
• While writing the molecular formula of
monosaccharides, the spatial arrangements of
H and OH groups are important , since they
contain assymetric carbon
26. ASSYMETRIC CARBON
• Means that 4 different groups are attached to the same
carbon
• Glyceraldehyde is the simplest monosaccharide with one
assymetric carbon
27. A compound having one assymetric carbon may exists in
two forms , which are mirror images of each other.
The number of stereoisomers depends on the number of
asymmetric carbon atoms. This is given by a formula 2n.,
where n is the number of asymmetric carbon atoms
Glucose contain 4 asymmetric carbon, 16 isomers
28. Stereo isomers occur either D or L form.
This is based on the position of –OH group on the
reference carbon
In a glyceraldehyde, If the –OH is on right side of the
assymetric carbon, sugar is D series(D-Glyceraldehyde)
and if on left side , it belongs to L series(L-
Glyceraldehyde)
D and L isomers are mirror images of each other
D AND L ISOMERS
29. The penultimate carbon atom is used as reference
carbon while naming other higher monosacchrides.
The refernce carbon of glucose is C5.
30. OPTICAL ACTIVITY
Optical activity is exhibited by the compounds
having assymetric carbon atoms.
When a plane polarized light is passed through a
sugar solution, the light will be rotated either to the
right or to the left.
If the light is rotated to the right (clock wise), then
the molecule is said to be dextro rotatory rep: as ‘d’
or ‘+’.
If the light is rotated to the left (anticlock wise) then
the molecule is said to be levo rotatory rep: as ‘l’ or
‘-’.
31. Do not confuse D form and d form
D glucose is dextrorotatory, D fructose is
levorotatory
32. RACEMIC MIXTURES
Equimolar mixtures of d and l forms is called
racemic mixtures.
It does not rotate, d and l forms cancels each other.
33. • When two monosaccharides different from one another,
only in configuration with regard to single carbon other
than reference carbon atom , they are called epimers; and
they are said to be epimeric pairs
• Eg. Glucose and mannose are epimers with regard to
carbon 2(C2 epimers)
• D Glucose and D galactose are epimers with regard to
carbon 4 (C4 epimers)
EPIMERS
34. • The interconversion of epimers(glucose to galactose)
is known as epimerization and the enzymes known as
epimerase
39. ANOMERISM
Sugars in solution exist in the form of rings.
The ring is formed because of high reactivity of
carbonyl group of (-C=O) of both aldehyde and
ketone group
In aldohexose (glucose), a hemiacetal ring is
formed between 1st and 5th carbon
40.
41.
42.
43. This results in a ring form containing 5 carbon
atoms and 1 oxygen.
This structure is similar to that of the compound
pyran , Hence this six membered ring structure
called pyranose structure
The formation of ring structure makes carbon atom
number 1 is also asymmetric
There fore carbon atom 1 shows alpha or beta form
, depending on the position of –OH group of C1.
If the –OH group is present above the plane of ring
it is beta form, and if the –OH is below the plane it
is alpha form.
45. • Haworth projection formula are depicted by a six membered
ring pyranose( based on pyran) or a five membered
furanose ( based on furan)
• The cyclic form of glucose are known as α -D
glucopyranose and α -D gluco furanose
47. • The alpha and beta cyclic forms of D glucose are
known as anomers
• They differ from each other in the configuration only
around C1 known as anomeric carbon
• The anomers differ in their physical and chemical
properties
48. MUTAROTATION
• The alpha and beta anomers of glucose have
different optical rotations
• The specific optical rotation of a freshly prepared
glucose(alpha) solution in water is +112.2o,which
gradually changes and attains an equilibrium with
constant value of +52.7o
49. • In the presence of alkali, the decrease in optical rotation
is rapid
• The optical rotation of beta glucose is +18.7o
• Muta rotation is defined as change in the specific
optical rotation representing the interconversion of
alpha and beta forms of D-glucose to an equilibrium
mixture
53. GLYCOSIDE FORMATION
TWO CARBOHYDRATES ARE JOINED
BYGLYCOSIDIC BOND
THE –OH GROUP OF ANOMERIC CARBON OF
ONE CARBOHYDRATE IS JOINED BY A
COVALENT BOND TO THE –OH GROUP OF
ANOTHER MOLECULE, THIS IS THE
GLYCOSIDIC BOND.
54. ACTION OF STRONG ACIDS
On heating with acids sugar forms furfural
derivatives
These furfural form colored complexes with
alphanaphthol or resorcinol
Molisch test
Seliwanoffs test
56. ACTION OF ALAKALI
On treating with alkali, sugars become good
reducing agents
Only sugars with aldehyde or ketone group act as
reducing agent as they form enediols
Benedicts test
57. BENEDICT’S TEST
• Benedict’s reagent contain sodium carbonate, copper
sulfate and sodium citrate
• This test is commonly employed to detect the presence
of glucose in urine
• To 5ml benedict’s reagent add 8drops of sugar solution,
mix and boil for 3 minutes to form red precipitate
58. • Depending upon the amount of sugar present,
benedict’s reagent gives different colored
precipitate ranging from green , yellow to red
59. • In alkaline medium sugars form enediol
• Enediols are strong reducing agent converting cupric ions of
benedict’s reagent in to cuprous ions which ultimately forms
cuprous oxide as a red precipitate
glucose 1-2 ene
diol
Benedict’s
reagent Cu2+ Cu+ Cu2O
Red ppt
Alkaline
medium
61. ACTION OF WEAK ACID
BARFOEDS TEST
SUGAR SOLUTION WITH BARFOEDS REAGENT ,
WHEN HEATED, REDUCES CUPRIC TO CUPROUS
ION
BARFOED’S REAGENT CONTAIN COPPER ACETATE
IN DILUTE ACETIC ACID
62. OXIDATION – SUGAR ACID
FORMATION
• Depending on the oxidizing agent used, the terminal
aldehyde(keto) group or the terminal alcohol or both groups
may be oxidized
• With Hypobromous as oxidizing agent
• Oxidation of aldehyde group in glucose results in the
formation of gluconic acid
• Mannose to mannonic acid
• Galactose to galactonic acid
63. • With nitric acid as oxidising agent
• Oxidation of terminal alcohol group leads to the
formation of uronic acid
• Glucose to glucuronic acid
64. REDUCTION TO FORM ALCOHOLS
• When treated with reducing agents (Na/Hg), the
aldehyde or keto group is reduced to alcohol
• Glucose to sorbitol
• Galactose to dulcitol
• Mannose to mannitol
• Ribose to ribitol
• Fructose to mannitol and sorbitol
65. • Sorbitol , mannitol and dulcitol are used to identify
bacterial colonies
• Mannitol is also used to reduce intra cranial
tension by forced diuresis
• Sorbitol and dulcitol when accumulate in tissues in
large amounts cause strong osmotic effects leading
to swelling of cells and certain pathological
condition it cause cataract
66. ACTION WITH PHENYL HYDRAZINE
(OSAZONE FORMATION)
• All reducing sugars will form osazone with excess of phenyl
hydrazine in acetic acid
• Osazones are insoluble
• Each sugars have characteristic crystal form of osazone
• Glucose + phenyl hydrazine
Glucohydrazone
Glucosazone
phenyl hydrazine
67. • Glucose , fructose . mannose form same
type osazones(needle shape)
• Lactose form powder puff crystal or pin
cushion crystal
• Maltose form sunflower shape crystal
75. The differences in glucose, fructose and mannose
are dependent on the first and second carbon atoms
These carbons are involved in osazone formation
These differences are masked when binding with
phenyl hydrazine
Hence these 3 sugars will produce same needle
shape crystal
76. FORMATION OF GLYCOSIDES
• When the hemi acetal or hemiketal hydroxyl group of
anomeric carbon of a carbohydrate reacts with OH group
of another carbohydrate or a non carbohydrate(methyl
alcohol, phenol or glycerol)
• The bond so formed is known as glycosidic bond and the
non carbohydrate moiety is known as aglycone
77. • Glycosidic bond may be alpha or beta depending on the
configuration of sugar contributing the 1st carbon atom for the
formation of glycosidic bonds.
• For ex: lactose has beta 1, 4 glucose units
• Starch has glucose units linked by alpha 1,4 glycosidic bonds
78. DERIVATIVES OF MONOSACCHARIDES
• Amino sugars
• Amino groups may be substituted for –OH group
of sugars to give rise to amino sugars
• Generally amino group is added to second carbon
atom of hexoses
• Glucosamine
• Galactosamine
79. • Amino groups of amino sugars are some time acetylated
• N-acetyl D glucosamine(Glu Nac)
• N-acetyl D galactosamine(Gal Nac)
80. •Deoxy sugars
• Oxygen of the hydroxyl group may be removed
to form deoxy sugars
• Deoxy ribose
82. • Disaccharides consist of 2 monosaccharides(same or different)
held together by a glycosidic bond
• They are of 2 types
• Reducing disaccharides with free aldehyde or keto group eg
maltose and lactose
• Non reducing disaccharides with no free aldehyde or keto
group eg. sucrose
83. • Composed of 2 alpha glucose units held together by
alpha (1-4) glycosidic bond
• C1 of one glucose and C4 of the other, leaving one free
anomeric carbon of second glucose , which can act as
reducing agent
• Thus maltose is a reducing disaccharide
• Maltose form sunflower shaped crystals in osazone test
• Maltose is the hydrolytic product of starch
Maltose
85. • Sugar present in milk
• Reducing disaccharide
• It is made of one galactose and glucose unit joined by Beta 1,
4 glycosidic bond
• On hydrolysis lactose forms beta galactose and alpha glucose
• Lactose form powder puff crystal with osazone
• The anomeric carbon of C1 glucose is free, hence lactose
exhibits reducing properties
Lactose
86.
87. • Present in sugar cane and fruits
• sweetening agent known as Cane sugar
• Made of one molecule of glucose and fructose joined by α-
1,β-2-glycosidic linkage.
• Sucrase enzyme split it in to glucose and fructose
• Sucrose does not have free anomeric –OH group so it is non
reducing. It cannot reduce benedict’s test
• Non reducing sugar and not form osazone
Sucrose
88. Sucrose shows the property of inversion
It is dextrorotatory in nature, after hydrolysis, it
gives a mixture of glucose and fructose.
This mixture has levorotation
Thus the direction of rotation changes after the
compound is hydrolyzed. This is called inversion
Equimolar mixtr of glucose and fructose(ie
hydrolysed product thus formed )is called invert
sugar
Enzyme converting hydrolysis sucrase or invertase
89. SUCROSE
1
2
- D glucose Β-D fructose
Both the functional groups are held together and protected from oxidative
attacks. Therefore it is known as NON REDUCING
93. POLYSACCHARIDES
• Carbohydrates composed of 10 or more
monosacharides are called polysaccharides
• Polysaccharides joined together by glycosidic
bonds
• It is also known as glycans
95. • Homopolysaccharides (homoglycans)-single
kind of monosaccharide units repeated again
and again
• Ex: starch , glycogen
Note :
• Glucans are polymers of glucose
• Fructosans are polymers of fructose
98. STARCH
It is the reserve carbohydrate form in
plants(storage form)
Starch is composed of amylose(unbranched) and
amylopectin(branched) molecule
On hydrolysis both amylose and amylopectin gives
many molecules of glucose
99. It is a linear polymer of60-600 D-glucose units
joined by alpha 1-4 linkage
The last glucose at one end of each chain carries a
free anomeric C-OH group
This end is reducing end
Other end is non reducing end
amylose
100. AMYLOPECTIN
It is structurally identical to that of amylose (alpha 1-4
linkage ) but the side chain joining them by alpha 1-6
linkage
Thus amylopectin is a branched polymer having both
(alpha 1-4 linkage and alpha 1-6 linkage
101. • Starches are hydrolysed by amylase
to liberate dextrins and finally
maltose and glucose units
• Amylase acts in alpha 1-4 glycosidic
bonds
102. • Starch forms blue color with iodine
,this color disappears on heating and
reappears when cooled. This is a
sensitive test for starch
• Starch is non reducing because free
reducing groups are absent
103. GLYCOGEN
Reserve carbohydrate in animals
Stored in liver and muscle
High concentration in liver
Structure is similar to that of amylopectin with more
number of branches
Glucose is the repeating unit in glycogen joined together
by alpha 1-4 glycosidic bond and alpha 1-6 at
branching points
GLYCOGEN IS MORE BRANCHED AND MORE
COMPACT THAN starch
104. CELLULOSE
It is structural homoglycan of plant fiber.
Main constituent of plant cell wall.
It is totally absent in animals
Cellulose is composed of 300-3000 β glucose units linked
by ß –1,4 glycosidic bond
It is a straight line structure
with no branching points
105. Beta 1-4 linkages are hydrolysed by enzyme
cellobiase
But this enzyme is absent in animals and human
digestive system and hence cannot be digested
Though it is not digested , it has great
importance in human nutrition
It is a major constituent of fiber, the non
digestable carbohydrate
106. DEXTRAN
Complex, branched glucan(polysaccharide
made of many glucose units) composed of
chains of varying length
It is used medicinally as an antithrombotic,
to reduce blood viscosity, and as volume
expander in anemia
107. DEXTRIN
Break down product of starch by
enzyme amylase
Made up of many glucose units bound
by alpha 1-4 glycosidic bond and
alpha 1-6 at branching points
They are the products of partial
hydrolysis of starch.
108. CHITIN
◊Composed of units of N acetyl
glucosamine combined by beta 1-4
glycosidic bonds
◊It is present in exoskeleton of insects
109. INULIN
• It is a long chain composed of D fructose
units with beta 1,2 linkages
• i.e. it is a polymer of fructose
• It is clinically used to find renal clearance
and glomerular filtration rate
110. HETEROPOLYSACCHARIDES
• Polysaccharides are composed of different types
of sugars or their derivatives, they are known as
heteropolysachharides or heteroglycans
Examples
• Glycosaminoglycans(mucopolysaccharides)
• Agar
• Agarose
111. Long, Unbranched heteropolysaccharide, made of repeating
disaccharide units containing uronic acid & amino sugars.
Amino sugar – Glucosamine or Galactosamine
Uronic acid – D-Glucuronic acid or L-Iduronic acid
GAGs are the most important group of heteroglycan in humans.
First isolated from mucin so called mucopolysaccharides
Major components of extracellular matrix of connective tissue,
including bone and cartilage, synovial fluid, vitreous humor and
secretions of mucus producing cells.
Glycosaminoglycans or mucopolysaccharides
112. • Some of the mucopolysaccharides are found in
combination with protein to form mucoproteins or
proteoglycans
• Mucopolysaccharides are essential components of
tissue structure
• The extra cellular spaces of tissue consist of
collagen and elastin fibers embedded in a matrix or
ground substances
• The ground substances is composed of GAG
113. HYALURONIC ACID
• Contain glucosamine and glucuronic
acid]
• It serves as a lubricant and shock
absorbent in joints and promotes
wound healing
• Present in connective tissues, tendons,
115. CHONDROITIN SULPHATE
• Major constituent of various mammalian
tissues
• Structurally it is comparable with hyaluronic
acid
• Composed of D glucuronic acid and N-acetyl
galactosamine sulphate
• It maintain the structure and shapes of the
tissues
116. DERMATAN SULPHATE
• Mostly occurs in skin
• Structurally similar to chondrioitin sulphate
• Composed of iduronic acid and
N-acetylgalctosamine sulphate
Maintains the shapes of tissues
117. KERATAN SULPHATE
• Only GAG without any uronic acid
• Units are galactose and N acetyl
glucosamine
• Found in cornea and tendons
• Keeps cornea transparent
118. Agar
Contains galactose, glucose & other sugars. Obtained from sea weeds
Functions: • Cannot be digested by bacteria. • So used as supporting agent
to culture bacterial colonies. • Also as support medium of immuno diffusion &
immuno-electrophoresis.
. Agarose
Galactose and 3,6 anhydrous galactose units
Used as matrix for electrophores
119. • Glycoproteins are proteins that
contain oligosaccharide chains (glycans) covalently
attached to polypeptide side-chains.
• These include their role as enzymes , hormones ,
transport proteins , structural proteins and receptors
• Collagen- structure
• Hydrolases- enzymes
• Ceruloplasmin – transport
• Immunoglobulins-defense against antigen
120. Reference Books
Text Book of Biochemistry- Harper
Text Book of Biochemistry - Dr. U.Satyanarayana
Text Book of Medical Biochemistry-DM.Vasudevan
Text Book of Medical Biochemistry – MN Chatterjea
