Carbohydrates are polyhydroxy aldehydes or ketones that serve important functions in the body. They provide energy, act as energy stores, and are structural components of cells. Glucose is the main energy source and is either used immediately or stored as glycogen. Other important carbohydrates include fructose, galactose, and mannose. Carbohydrates undergo various reactions and exist in multiple isomeric forms including structural isomers, stereoisomers, anomers, and epimers. Proper identification and analysis of carbohydrates is important for understanding their roles in biochemical processes.

1. CARBOHYDRATE
CHEMISTRY
Dr. Mithilesh Kumar Singh
Department of Biochemistry
Noida International Institute of Medical Sciences
Gautam Budha Nagar, UP

2. Carbohydrate are polyhydroxy aldehyde or ketone or compound which yield these on
hydrolysis.
• Polyhydroxy aldehydes – Glucose, Mannose
• Polyhydroxy ketones – Fructose, Ribulose
• Compounds which produce these on hydrolysis – Lactose, Starch, Glycogen, etc
General Molecular formula:
Cn(H2O)n
Eg: Glucose – C6H12O6
INTRODUCTION

3. 1. Main source of energy. RBCs and Brain wholly dependents on carbohydrates. Energy
production from carbohydrates will be 4 kcal/g.
2. Storage form of energy (in plant as STARCH and in animals as GLYCOGEN)
3. Carbohydrate converted into fat if its in EXCESS.
4. Components of cell membrane and receptors are GLYCOPORTEINS and
GLYCOLIPIDS.
5. Structural basis of many organisms:
• Cellulose of plants
• Exoskeleton of insects
• Cell wall of microorganisms
• Mucopolysaccharides as ground substance in higher organism
BIOMEDICAL IMPORTANCE OF CARBOHYDRATES

4. 6. Glucose is only molecule that can be utilized anaerobically.
7. Glycogen serve as a source of energy during fasting.
8. Glycoconjugates are important for the structure of cell membrane and cellular functions
(cell growth, adhesion and fertilization).
9. Ribose and deoxyribose are the components of nucleic acid (DNA and RNA) and
nucleotides.

5. CARBOHYDRATE
Based on Sugar Group Based on Attached Group
Based on Number of Carbon Atom
NOMENCLATURE

6. NOMENCLATURE
On basis of sugar group:
• Monosaccharides – Polyhydroxy aldehydes or ketones
• Disaccharides – Two monosaccharides linked by glycosidic linkage
• Oligosaccharides – upto 10 monosaccharides linked by glycosidic linkage
(oligosaccharides include disaccharides also)
• Polysaccharides - >10 monosaccharides linked by glycosidic linkage
 Homopolysaccharides
 Heteropolysaccharides

7. On basis of attached group:
Aldehyde Group – Aldoses
Keto Group – Ketoses
On basis of number of carbon atom:
Triose (C3)
Tetrose (C4)
Pentose (C5)
Hexose (C6)
Heptose (C7)
and so on……

8. MONOSACCHARIDES
All monosaccharides can be considered as the hydrates of carbon.
For a molecule to be a polyhydroxy aldehyde or ketone, it should have atleast 3 carbon (one
carbon for carbonyl group and the other two for hydroxyl groups).
Glyceraldehyde and dihydroxy acetone are the simple sugars.
Glyceraldehyde is a 3-carbon carbohydrate with an aldehyde functional group while
dihydroxy acetone is a ketone.

9. No. of
Carbon
Atoms
Generic Name
Aldoses
(with aldehyde group)
Ketoses
(with keto group)
3 Triose Glyceraldehyde Dihydroxyacetone
4 Tetrose Erythrose Erythrulose
5 Pentose
Arabinose
Xylose
Ribose
Xylulose
Ribulose
6 Hexose
Glucose
Galactose
Mannose
Fructose
7 Heptose Sedoheptulose
CLASSIFICATION OF FUNCTIONAL GROUP

10. ISOMERISM IN CARBOHYDRATES
ASYMMETRIC CARBON means that four different groups are attached to the same carbon.

11. FUNCTIONAL ISOMERS OR CONSTITUTIONAL ISOMERS
Same molecular formula but the functional groups are different, i.e order of attachment of
atom is different.
So, these two are functional isomers of each other.
Isomerases are a class of enzyme that catalyse the reversible interconversion of isomers.
Eg. Phosphoglucose isomerase catalyses the interconversion of Glucose-6-Phosphate.
Other Functional Isomers:-
• Glucose and Fructose
• Ribose and Ribulose
• Xylose and Xylulose

12. STEREOISOMERS
Compound having same structural formula, but different in spatial configuration are known as
stereoisomers.
While writing the molecular formula of monosaccharides, the spatial arrangements of H and
OH groups are important, since they contain asymmetric carbon atoms.
The number of possible stereoisomers depends on the number of asymmetric carbon atoms by
the formula 2n (where n is number of asymmetric carbon atoms).

13. Asymmetric Carbon = ??
Stereoisomers = ??
Asymmetric Carbon = 1
Stereoisomers = 2n (2x1=2)

14. D and L ISOMERISM OF GLUCOSE
The 5th carbon atom of glucose is considered as reference carbon which form two mirror
images that is D and L forms.
The group in 2nd , 3rd , 4th and 5th carbon atom get totally reversed so as to produce mirror
images.
These two form are also stereoisomers.
D sugars are naturally occurring sugar and body can metabolized only D sugars.

15. OPTICALACTIVITY
Asymmetric carbon atom causes optical activity.
When the beam of plan polarized light is passed through a solution of carbohydrates, it will
rotate the light either to right or left.
Depending on the rotation, molecules are called dextrorotatory (+) (d) or levorotatory (-) (l).
D-glucose is dextrorotatory but D-fructose is levorotatory.
Equimolecular mixture of optical isomers has no net rotation is known to be RACEMIC
MIXTURE.

16. ENANTIOMERS
These are pair of stereoisomers that are non-superimposable mirror image of each other.
Eg.: D & L forms are enantiomers
Based on configuration of H and OH groups at second carbon atom two mirror image are
forms are denoted as D- and L- forms.
Therefore, penultimate carbon atom is the reference carbon atom for naming mirror
images.
This is also referred to as absolute configuration.

18. DIASTEREOISOMERS
Diastereoisomers (diastereomers) are stereoisomers which are NOT mirror images of each
other.
Configurational changes with regard to C2, C3 and C4 will produce eight different
monosaccharides.
Out of these only 3 are seen in human body these are:
• Glucose (C2 & C4)
• Galactose (C4)
• Mannose (C2)
There are eight diastereoisomers for aldohexoses.
With reference to C5, all of them will have D and L forms.
So the hexose represent 16 different monosaccharides, due to spatial arrangement.

19. CH2
-OH
O
H
OH
OH
O
H
CHO
CH2
-OH
O
H
OH
OH
O
H
CHO
D-galactose
D-mannose
Galactose and mannose are not epimers but diastereo-isomers

20. There are two special types of diastereoisomers:
• Epimers
• Anomers

21. EPIMERS
Epimers are diasteroisomers that differ around the configuration of a single asymmetric carbon
other than the anomeric carbon.
When the sugar are different from one another, only in configuration with regard to a single
carbon atom, other than the reference carbon atom, they are called epimers.

22. Glucose and Galactose are epimers of each other.
Glucose and Mannose are epimers to each other.
Mannose & Galactose are NOT epimers to each other.
They are Diastereomers because they differ in the orientation of more than one carbon atoms.
Epimers are a type of isomerase enzymes which convert one epimers to other.
Eg.: UDP-Glucose 4-epimerase catalyses the reversible conversion of UDP-Glucose to UDP-
Galactose.

23. D-galactose
4th epimer
Galactose and mannose are not epimers but diastereo-isomers
CH2
-OH
O
H
OH
OH
O
H
CHO
D-glucose
Epimers of D-glucose
D-mannose
2nd epimer
CH2
-OH
O
H
OH
OH
O
H
CHO
CH2
-OH
O
H
OH
OH
OH
CHO 1
2
3
4
5
6

24. Epimers of glucose can be remembered as
“MAGI”
Mannose is the C2 epimer
Allose is the C3 epimer
Galactose is the C4 epimer
L-Idose is the C5 epimer

25. ANOMERS
Anomers are special types of diastereomers that differ only around the anomeric
carbon – first carbon of glucose, second carbon in fructose.
Anomerism is seen ONLY in ring structure.

26. ANOMERISM IS DUE TO CYCLIZATION OF SUGARS
Alcohol react with an aldehyde to produce HEMIACETAL.
Alcohol react with a ketone to produce HEMIKETAL.
Glucose is a polyhydroxy aldehyde. So, it has both alcohol and aldehyde group
required for the formation of hemiacetal.
Hydroxyl group of 5th carbon of glucose reacts with aldehyde group (1st carbon) to
produce a intramolecular hemiacetal. This results in the formation of a 6-membered
cyclic structure known as PYRANOSE RING.
This cyclization converted the previously symmetric carbon of the linear chain to an
asymmetric carbon. This new asymmetric carbon is the anomeric carbon.

27. If the OH group of the anomeric carbon is above the plane of pyranose ring or at the
sample plane of the C6, it is know as β anomers.
If the OH group of the anomeric carbon is below the plane of pyranose ring or at the
opposite plane of the C6, it is know as α anomers.

28. When the C5 OH group of fructose reacts with the keto group at the 2nd carbon, a 5-
membered furanose ring is formed.

30. ISOMERS
Have same molecular formula but different structures
CONSTITUTIONAL ISOMERS
Differ in the order of attachment of
atoms
STEREOISOMERS
Atoms are connected in the same order
but differ in spatial arrangement
ENANTIOMERS
Non-superimposable mirror image
DIASTEREOISOMERS
Isomers that are not mirror images
EPIMERS
Differ at one of several asymmetric carbon atoms
ANOMERS
Isomers that differ at a new asymmetric
carbon atom formed on ring closure
OVERVIEW OF ISOMERS

31. MUTAROTAION
When D-glucose is crystallized at room temperature, and a fresh solution is prepared, its
specific rotation of polarized light is +112°; but after 12 – 18 hours it changes to +52.5°.
If initial crystallization is taking place at 98℃ and then solubilized, the specific rotation is
found to be +19°, which also changes to +52.5° within a few hours. This change in
rotation with time is called MUTAROTATION.

32. D-glucose has two anomers, alpha- and beta-varieties.
These anomers are produced by the spatial configuration with reference to first
carbon in aldoses and second carbon atom in ketoses. Hence these carbon atoms are
known as anomeric carbon atoms.
α-D-glucose has specific rotation of +112° and β-D-glucose has +19°. Both undergo
mutarotation and at equilibrium, one-third molecules are alpha type, and two-thirds
are beta variety, to get the specific rotation +52.5°.
Mutarotation is accelerated by acid/bases.
Mutarotation is prevented when the anomeric carbon is involved in the formation of
glycosidic bond.

33. Crystalline glucose (α-D-Glucopyanose) (+112°)
Spontaneous conversion of α anomers to β ----> change in optical
rotation (+19°)
Final equilibrium reached ----> optical rotation stable (+52.5°)
CONCEPT OF MUTAROTAION

34. SUGAR IMPORTANCE
Glucose • Predominant sugar in human body.
• Major source of energy.
• Present in blood.
• D-glucose is dextrorotatory.
• In clinical practice, it is often called as dextrose.
Galactose • Constitute of lactose (milk sugar), glycolipids and glycoproteins.
• Epimerise to glucose in liver and then utilized as energy sources.
Mannose • Constitute of glycoprotein, globulins and mucoproteins.
• Isolated from plant mannans.
Fructose • Constitute of sucrose, the common sugar.
• D-fructose is levorotatory.
HEXOSES OF PHYSIOLOGICAL IMPORTANCE

35. THREE REPRESENATION OF GLUCOSE STRUCTURE
The 1st carbon, aldehyde group is condensed with the hydroxyl group of the 5th
carbon to form a ring.
Ring structure represents hemiacetal form, which is the condensation of an aldehyde
(or keto) with a hydroxyl group.
The open chain projection formula and hemiacetal ring structure of glucose were
proposed by E Fischer, hence called Fischer’s formula.
Later, its showed that glucose exists as a pyranose ring.

36. REPRESENATION OF D-GLUCOSE STRUCTURE

37. FRUCTOSE IS A KETOHEXOSE
In fructose, the keto group is on 2nd carbon atom. Thus second carbon atom is the
anomeric carbon atom.
Fructose has four isomers. Each of them has D & L forms with regard to 5th carbon
atom.
Fructose has same molecular formula as glucose, but differs in structural formula.
So glucose and fructose are functional group (aldose-ketose) isomers.
D-fructose is levorotatory.
Only D varieties is seen in biological systems.
Fructose remains predominantly as furanose ring structure.
Fructose is major constituent of honey.

38. REPRESENATION OF D-FRUCTOSE STRUCTURE

39. REACTION OF MONOSACCHARIDES
In sugars, the following 3 properties will be seen together:
• Mutarotation
• Reducing property
• Formation of osazone with phenylhydrazine

40. ENEDIOL FORMATION
In mild alkaline solutions, carbohydrates containing a free sugar group (aldehyde or
keto) will tautomerise to form enediols.
In mild alkaline conditions, glucose is converted into fructose and mannose.
Since endiols are highly reactive, sugar are powerful reducing agents in alkaline
medium.

41. BENEDICT’S REACTION
Benedict's reagent is very commonly employed to detect the presence of glucose in urine
(glucosuria).
It is a standard laboratory test employed in diabetes mellitus.
Benedict's reagent contains :
• Sodium carbonate
• Copper sulphate
• Sodium citrate
Any sugar with free aldehyde/keto group will reduce the Benedict’s reagent.
Therefore, this is not specific for glucose.

42. REDUCING SUBSTANCES IN URINE
SUGARS NON-CARBOHYDRATES
Glucose Vitamin C (Ascorbic Acid)
Fructose Salicylates
Lactose Homogentisic Acid
Galactose Glucuronides of Drugs
Pentose

43. OSAZONE FORMATION
All reducing sugars will form osazones with excess of phenylhydrazine when kept at boiling
temperature.
Osazones are insoluble.
Each sugar will have characteristic crystal form of osazones.
Osazones may be used to differentiate sugars in biological fluids like urine.

45. OXIDATION OF SUGARS
Under mild oxidation condition the aldehyde group is oxidized to carboxyl group to produce
aldonic acid.
Glucose is oxidized to Gluconic Acid
Mannose is oxidized to Mannonic Acid
Galactose is oxidized to Galactonic Acid
When aldehyde group is protected, and the molecule is oxidized, the last carbon becomes
COOH group to produce URONIC ACID.
The glucuronic acid is used by the body for conjugation with insoluble molecules to make
them soluble in water for detoxification purpose and also for synthesis of hetero-
polysaccharides.

46. Under strong oxidation conditions (nitric acid+heat), the first and last carbon atoms are
simultaneously oxidized to from dicaboxylic acids, known as SACCHARIC ACID.
Glucose oxidized to glucosaccharic acid
Mannose to mannaric acid
Galactose to mucic acid.
Mucic acid forms insoluble crystals, and is the basis for a test for identification of galactose.

47. Gluconic acid Glucuronic Acid Glucosaccharic acid

48. FURFURAL DERIVATIVES
Monosaccharides when treated with concentrated sulfuric acid undergoes dehydration with the
removal of three molecules of water.
Therefore hexoses give hydroxymethyl furfural and pentoses gives furfural.
The furfural derivative can condense with phenolic compounds to give colored products.
This forms the basis of Molisch test which is general test for carbohydrates.

49. REDUCTION TO FORM ALCOHOLS
When treated with reducing agents such as sodium amalgam, hydrogen can reduce sugars.
Aldose yields corresponding alcohol.
Ketose form two alcohols, because of appearance of new asymmetric carbon atom in this
process.
Glucose is reduced to sorbitol; mannose to mannitol
Fructose reduced to sorbitol and mannitol.
Galactose is reduced to dulcitol
Ribose to ribitol

50. Sorbitol, mannitol and dulcitol are used to identify bacterial colonies.
Mannitol is also used to reduce intracranial tension by forced diuresis.
The osmotic effect of sorbitol and dulcitol produces changes in tissues when they acculmulate
in abnormal amounts, eg cataract of lens.

51. Glucose Sorbitol Fructose Mannitol

52. GLYCOSIDES
When hemiacetal group (hydroxyl group of the anomeric carbon) of monosaccharide is
condensed with an alcohol or phenol group, it is called as GLYCOSIDE.
The non-carbohydrate group is called AGLYCONE.
Glycosides do not reduce Benedict’s Reagent, because the sugar group is masked.
They may be hydrolyzed by boiling with dilute acid, so that sugar is free and can then reduce
copper.
Alpha-glycosides are hydrolyzed by maltase from yeast, while beta-glycosides are hydrolyzed
by emulsion from almonds.

53. Sugar + Aglycon = Glycoside Source Importance
Glucose + phloretin Phlorhizin Rose bark Renal damage
Galactose+ digitogenin + xylose Digitonin Leaves of foxglove Cardiac stimulant
Glucose + indoxyl Plant indican Leaves of indigofera Stain

54. FORMATION OF ESTERS
Hydroxyl groups of sugars can be esterified to form acetates, propionates, benzoates,
phosphates, etc.
Sugar phosphates are of great biological importance.
Metabolism of sugars inside the body starts with phosphorylation.
Glucose-6-phosphate and glucose-1-phosphate are important intermediaries of glucose
metabolism.

55. AMINO SUGARS
Amino groups may be substituted for hydroxyl groups of sugars to give rise to amino sugars.
Generally, amino group is added to the second carbon atom of hexoses.
Amino sugars will not show reducing property.
They will not produce osazones.

56. Glucosamine is seen in hyaluronic acid, heparine, and blood group substances.
Galactosamine is present in chondroitin of cartilage, bone and tendons.
Mannosamine is a constituent of glycoproteins.
Amino group in sugar may be further acetylated to produce N-acetyl-glucosamine, N-acetyl-
galactosamine, etc which are important constituent of glycoproteins, mucoproteins and cell
membrane antigens.

57. DEOXY SUGARS
Oxygen of the hydroxyl group may be removed to form deoxy sugars.
Deoxy sugars will not reduce and will not form osazomes.
L-fucose is present in blood group antigens and many other glycoproteins.
Deoxyribose is an important part of nucleic acid.

58. PENTOSES
It contain five carbon atoms.
Ribose is constituent of RNA.
Ribose is also seen in co-enzymes such as ATP and NAD.
Deoxyribose is seen in DNA.
Ribulose is an intermediate of HMP shunt pathway.
Arabinose is present in cherries and seen in glycoproteins of body.
Xylose is seen in proteoglycans.
Xylulose is an intermediate of uronic acid pathway.

59. GLYCOSIDIC LINKAGE
Alcohol when react with aldehyde it forms HEMIACETAL, when hemiacetal react with
another alcohol it form ACETAL.
Alcohol when react with ketone it forms HEMIKETAL, when hemiketal react with another
alcohol it form KETAL.
Formation of acetal and ketal is the basis of a Glycosidic Bond.
A glycosidic bond is a covalent bond formed between the hemiacetal or hemiketal group
of a sugar and the hydroxyl group of another sugar or non-sugar compound (aglycone)
or amino/amide group.
Glycosidic bond can be α or β depending upon the configuration of the sugar that donates
the hemiacetal group.

60. TYPE OF GLYCOSIDIC BOND
Based on the LINKAGE –
O-glycosidic Bonds: Linkage between all disaccharide and polysaccharides
N-glycosidic Bonds: Linkage between sugar and base in nucleosides
Based on the ANOMERIC CARBON of HEMIACETAL DONOR –
α glycosidic bond – hemiacetal contains α anomer
β glycosidic bond – hemiacetal contains β anomer

61. DISACCHARIDES
When two monosaccharides are combined together by glycosidic linkage, disaccharides is
formed.
The important disaccharides are:
• Sucrose
• Lactose
• Maltose
• Isomaltose

62. SUCROSE
Also known as cane sugar.
Sucrose = Glucose + Fructose
Sucrose is non-reducing sugar.
It will not form osazone.
This is because the linkage involves first carbon of glucose and second carbon of fructose, and
free reducing groups are not available.
When sucrose is hydrolyzed, the products have reducing action.

64. A sugar solution which is originally non-reducing, but become reducing after hydrolysis, is identified as
sucrose (specific sucrose test).

65. Hydrolysis of sucrose (optical rotation +66.5°) will produce one molecule of glucose
(+52.5°) and one molecule of fructose (-92°). Therefor the products will change the
dextrorotatory to levorotatory, or the plane of rotation is inverted.
Equimolecular mixture of glucose and fructose thus formed is called INVERT SUGAR.
The enzyme producing hydrolysis of sucrose is called SUCRASE or INVERTASE.
Honey contains invert sugar.
Invert sugar is sweeter than sucrose.

66. LACTOSE
It is sugar present in milk.
It is reducing disaccharide.
Lactose = Glucose + Galactose
On hydrolysis lactose yields glucose and galactose.
Beta-glycosidic linkage is present in lactose.

68. The anomeric carbon atom is beta-galactose is attached to the 4th hydroxyl group of glucose
through beta-1,4 glycosidic linkage.
The lactose may be alpha or beta variety, depending on the configuration of 1st carbon of
glucose moiety.
Lactose forms osazone which resembles “badminton ball” or “hedgehog” or flower of “touch-
me-not” plant.
Lactose – milk sugar, disaccharide made of galactose and glucose.
Lactate or lactic acid is product of anaerobic metabolism of glucose.

69. MALTOSE
Maltose contain two glucose residues.
There is alpha-1,4 linkage, i.e the anomeric 1st carbon atom of one glucose is combined with
the hydroxyl group of another glucose through alpha-glycosidic linkage.
Maltose may be alpha or beta depending on the configuration at the free anomeric carbon
atom.
It is a reducing disaccharide.
It forms petal shaped crystals of maltose-osazone.

71. ISOMALTOSE
It is also a reducing sugar.
It contains two glucose units combined in alpha-1,6 linkage.
Thus first carbon of one glucose residue is attached to the 6th carbon of another glucose
through a glycosidic linkage.
Partial hydrolysis of glycogen and starch produces isomaltose.
The enzyme oligo-1,6-glucosidase present in intestinal juice can hydrolyze isomaltose into
glucose units.

73. DISACCHARIDES MONOSACCHARIDES
UNITS
LINKAGE ROLE
SUCROSE
(Cane Sugar)
Glucose + Fructose α-D-Glucose (12) β-D-Fructose Non-reducing sugar
Rare deficiency of sucrase leads to
sucrose intolerance
LACTOSE
(Milk Sugar
Glucose + Galactose β-D-Galactosyl (14) β-D-Glucose Deficiency of lactase leads to lactose
intolerance
MALTOSE
(Malt Sugar)
Glucose + Glucose α-D-Glucosyl (14) α-D- Glucose Amylase hydrolyse linear chain of
starch to generate maltose
ISOMALTOSE Glucose + Glucose α-D-Glucosyl (16) α-D- Glucose Amylase hydrolyse branch point of
starch to generate isomaltose

74. POLYSACCHARIDE
These are the polymerized products of many monosaccharide units.
They may be:
Homoglycans – Composed of single kind of monosaccharides, eg – Starch, glycogen
and cellulose.
Heteroglycans – Composed of two or more different monosaccharides, eg –
hyaluronic acid, chondroitin sulfate.

76. HOMOPOLYSACCHARIDE
Also known as homoglycans.
Composed of single type of monosaccharide.
Polymers of glucose are known as GLUCOSANS
Eg: Starch and Cellulose
Polymer of Fructose are known as FRUCTOSANS
Eg: Inulin

77. POLYSACCHARIDE
MONOMERIC
UNIT
LINKAGE ROLE
Cellulose Glucose β (14)
Structural polysaccharide of
plants
Dietary fiber
Starch Glucose α (14) and less α (16)
Storage polysaccharide of plants
Major carbohydrate in diet
Glycogen Glucose
α (14) and more α (16)
compared to starch
Storage polysaccharide of
animals
Dextran Glucose α (16) and α (13)
Used as plasma expander,
lubricant in eye drops and
vaccine preservative
Chitin N-acetyl glucosamine β (14)
Structural polysaccharide of
insects and fungi
Inulin Fructose β (12) Dietary fiber
Pectin D-Galacturonic acid α (14) Dietary fiber

78. HETEROPOLYSACCHARIDES
When the polysaccharides are composed of different types of sugars or there derivatives,
they are referred to as heteropolysaccharides or heteroglycans.
It is also called as MUCOPOLYSACCHARIDES because they were first discovered in mucin.
They consist of a repeating disaccharides unit made up to two different monosaccharides.

79. One of these is an amino sugar, (usually N-acetyl-gucosamine or N-acetyl-galactosamine).
The other monosaccharide is usually a uronic acid – either glucuronic or iduronic acid.
Due to amino sugar content, they are also commonly called as GLYCOAMINO-GLYCANS (GAG).

80. Some of the mucopolysaccharides are found in combination of mucoproteins or mucoids or
proteoglycans.
Mucoproteins may contain up to 95% carbohydrate and 5% protein.
Mucopolysaccharides are essential components of tissue structure.

81. The extracellular spaces of tissue (particularly connective tissue - cartilage, skin, blood
vessels, tendons) consist of collagens and elastin fibers embedded in a matrix or ground
substance.
The ground substance is predominantly composed of GAG.

82. FUNCTION
1. Form ground matrix substances to bind the tissues together.
2. They are present in various body fluid * and perform different functions*
3. Form the cell wall in plants and a number of plant resins that find human applications as
food additives or medicines.
4. Mediate a number of cell – cell or hormone – receptor interactions.

83. 5. They are present in all the plasma membrane glycoproteins that project outside the cells
and through which the other molecules or tissues get attached to the cells.
6. Perform a variety of function like transport, biological action (eg. Anticoagulation).
7. Regulate the exchange of ions between the extracellular and intracellular compartments
through ion channels.

84. GAG ARE HETEROPOLYSACCHARIDES OF EXTRA CELLULAR MATRIX
The extra cellular space in the tissues of multicellular animals is filled with a gel-like material,
the extracellular matrix (ECM), also called ground substance, which holds the cells together
and provides a porous pathway for the diffusion of nutrients and oxygen to individual cells.

85. The ECM that surrounds fibroblasts and other connective tissue cells is composed of an
interlocking meshwork of heteropolysaccharides and fibrous proteins such as fibrillar
collagens, elastins, and fibronectins.
Basement membrane is a specialised ECM that underlies epithelial cell; it consists of
specialized collagens, laminins and heteropolysaccharides.

86. GLYCOAMINO-GLYCANS
(GAG)
DISACCHARIDE UNIT
Hyaluronic Acid N-Acetylglucosamine
β1--->3 Glucuronic Acid
Chondroitin Sulphate N-Acetylgalactosamine
β1--->3 Glucuronic Acid
Keratan Sulphate N-Acetylglucosamine
β1--->3 Galactose
Dermatan Sulphate N-Acetylgalactosamine
β1--->3 Glucuronic Acid
Heparin N-Acetylglucosamine
ἀ1--->4 Iduronic Acid
MUCOPOLYSACCHARIDES AND THEIR REPEATING UNITS

87. HYALURONIC ACID
Hyalos :- glass (hyaluronic can have glassy or translucent appearance).
It is an important GAG found in the ground substance of synovial fluid of joints and vitreous
humor of eyes.
It is also present as a ground substance in connective tissues and forms a gel around the
ovum.

88. Hyaluronic acid serves as a lubricant and shock absorbant in joints.
It is composed of repeating units of N-Acetylglucosamine beta 1,4-glucuronic acid beta 1-
3-N-Acetylglucosamine and so on i.e. it is composed of alternate unit of D-glucuronic acid and
N-acetyl D-glucosamine.
These two molecules form disaccharide units held together by β (1 3) glycosidic bond.

89. HYALURONIC ACID

90. Hyaluronic acid contains up to 50,000 repeating disaccharide units (held by β 1 4 bonds)
with a molecular weight of several million; it form clear, highly viscous solution that serve as
lubricants in the synovial fluid of joints and give vitreous humor of the eye.
Hyaluronic acid is also a component of extracellular matrix of cartilage and tendons, to
which it contributes tensile strength and elasticity as a result of its strong noncovalent
interaction with other components of the matrix.
An enzyme secreted by some pathogenic bacteria, can hydrolyze the glycosidic linkages of
hyaluronic acid, rendering tissues more susceptible to bacterial invasion.

91. Other GAG differ from hyaluronic acid in three respects:
I. They are generally much shorter polymers
II. They are covalently linked to specific proteins (proteoglycans)
III. One or both monomeric units differ from those of hyaluronic acid

92. CHONDROITIN SULFATE
Chondros – cartilage
Chondroitin sulfate is the major constituent of various mammalian tissues i.e. bone, cartilage,
heart, valves, skin, cornea, etc.
Structurally, it is comparable with hyaluronic acid.
It is composed of repeating disaccharide units of D-Glucuronic Acid and N-Acetyl D-
Galactosamine 4 - Sulfate.

93. CONDROITIN 4-SULFATE

94. KERATAN SULFATE
Keras mean HORN
It is only GAG which does not contain any uronic acid.
The repeating units are galactose and N-acetyl-glucosamine in beta linkage.
It is found in cornea, cartilage, bone, and variety of horny structures formed of dead cell:
horn, hair, nails.

95. KERATAN SULFATE

96. DERMATAN SULFATE
It contains L – Iduronic Acid and N-Acetylgalactosamine in beta – 1,3 linkages.
It is found in skin, blood vessels and heart valves.

97. DERMATAN SULFATE

98. HEPARIN
Hepar mean LIVER.
It is originally isolated from dog liver.
It is produced by all animal cells and contains variable arrangement of SULFATES and NON
SULFATED SUGARS.
The sulfated segments of the chain allow it to interact with a large number of proteins,
including growth factors and ECM components, as well as various enzymes and factors
present in plasma.
Heparin is a fractionated form of haparin sulfate derived mostly from mast cell.

99. Heparin is a therapeutic agent used to inhibit coagulation through its capacity to bind the
protease inhibitor antithrombin.
Heparin binding causes antithrombin to bind to and inhibit thrombin, a protease essential to
blood clotting.
The interaction is strongly electostatic; heparin has the highest negative charged density of
any known biological macromolecule.
Purified heparin is routinely added to blood samples obtained for clinical analysis and to
blood donated for transfusion, to prevent clotting.

100. Sulfated Glucosamine–Alpha–1,4–Iduronic Acid
HEPARIN

101. The structure shown is determined by spectroscopy.
The carbon in the iduronic acid sulfate are colored BLUE.
The glucosamine sulfate are colored GREEN.
Oxygen are colored RED.
Sulfur atoms are colored YELLOW.

102. GLYCOPROTEINS AND MUCOPROTEINS
Some of the mucopolysaccharides are found in combination of mucoproteins or
proteoglycans.
When the carbohydrate chains are attached to a polypeptide chain it is called a
PROTEOGLYCAN.
If the carbohydrate content is less than 10%, it is generally named as a GLYCOPROTEIN.
If the carbohydrate content is more than 10%, it is a MUCOPROTEIN.

103. They are seen in almost all tissues and cell membranes.
About 5% of the weight of cell membrane is carbohydrate.
If carbohydrate groups cover the entire surface of the cell membrane, they are called
GLYCOCALYX.
Glycoprotein act as enzymes, hormones, transport proteins, structural proteins and receptors.

104. SYNDROME RELATED WITH GAG
Hunter syndrome
•Due to iduronate sulfatase deficiency.
•X link deficiency
•Degradation of dermatan sulfate and heparan sulfate are affected.
•Physical deformity and mental retardation , no corneal clouding
Hurler syndrome
•Coronary clouding, mental retardation, upper air obstruction.
•Degradation of dermatan sulfate and heparin are affected.
•Treated by bone marrow or cord blood transplantation.

105. Sly syndrome
•Hepatosplenomegaly, skeletal deformity, are seen.
•Degradation of dermatant sulfate and heparine are affected.
Sanfilippo syndrome
•Severe nervous system disorders, mental retardation.
•Four types enzymatic deficiency