1.
CHEMISTRY OF CARBOHYDRATES
DR. SWETA DAS

2.
OBJECTIVES
• Describe the nomenclature of carbohydrates
• Classification of carbohydrates.
• Structure and Isomerism in carbohydrates.
• Understanding the reactions of carbohydrates.

3.
DEFINITION
• Carbohydrates are polyhydroxy aldehydes or ketones, or
substances that yield such compounds on hydrolysis.
• Empirical formula (CH2O)n.
• Some also contain nitrogen, phosphorus or sulfur.
• The word “saccharide” is derived from the Greek “sakcharon”,
meaning "sugar“.

4.
CLASSIFICATION
CARBOHYDRATES
MONOSACCCHARIDES
ALDOSES
KETOSES
OLIGOSACCHARIDES POLYSACCHARIDES
HOMOPOLYSACCHARIDES
HETEROPOLYSACCHARIDES

5.
MONOSACCHARIDES
• Simple sugars
• Consist of a single polyhydroxy aldehyde or ketone
unit.
• The most abundant monosaccharide in Nature is the
six-carbon sugar D –glucose (dextrose).
• Monosaccharide of four or more carbons tend to have
cyclic structures.

6.
MONOSACCHARIDES
No of C-atoms Potentially active
carbonyl group
Trioses
Tetroses
Pentoses Aldoses Ketoses
Hexoses
Heptoses “These carbohydrates cannot
Octoses be hydrolyzed into simpler compounds”

7.
NO. OF CARBON
ATOMS
GENERIC NAME ALDOSES KETOSES
3 TRIOSE GLYCERALDEHYDE DIHYDROXYACETON
E
4 TETROSE ERYTHROSE ERYTHRULOSE
5 PENTOSE ARABINOSE
XYLOSE
RIBOSE
XYLULOSE
RIBULOSE
6 HEXOSE GLUCOSE
GALACTOSE
MANNOSE
FRUCTOSE
7 HEPTOSE SEDOHEPTULOSE

8.
TRIOSES

9.
Tetroses

10.
Pentoses

11.
Hexoses

12.
REPRESENTATIONS OF GLUCOSE
STRUCTURE
• The absolute configurations of sugars are known from x-
ray crystallography
• To represent three-dimensional sugar structures on
paper, we often use Fischer projection formulas .
• In Fischer projection formulas, horizontal bonds project
out of the plane of the paper, toward the reader; vertical
bonds project behind the plane of the paper, away from
the reader.

13.
• Alcohols react with the carbonyl groups of
aldehydes and ketones to form hemiacetals
and hemiketals, respectively.

14.
• The hydroxyl and either the aldehyde or the ketone groups
of monosaccharides can likewise react intramolecularly to
form cyclic hemiacetals and hemiketals.
• The configurations of the substituents to each carbon atom
of these sugar rings are conveniently represented by their
Haworth projection formulas

15.
• A sugar with a six-membered ring is known as a pyranose in
analogy with pyran, the simplest compound containing
such a ring. Similarly, sugars with five-membered rings are
designated furanoses in analogy with furan.
• The cyclic forms of glucose and fructose with six- and five
membered rings are therefore known as glucopyranose
and fructofuranose, respectively

16.
PROPERTIES OF MONOSACCHARIDES
1. Stereoisomerism
2. Diastereoisomerism
3. Optical activity
4. Epimerism
5. Anomerism
6. Mutarotation
7. Tautomerization

17.
STEREOISOMERS
• Compounds having same structural formula, but
different spatial configuration.
• The number of possible stereoisomers depends
on the number of asymmetric carbon atoms by
the formula 2^n [n= number of asymmetric
carbon atoms]

18.
STEREOISOMERS

19.
DIASTEREOISOMERS
• Configurational changes with regard to C2, C3,
C4 will produce 8 different monosaccharides.
• Only 3 are seen in human body : glucose ,
galactose , mannose.

20.
OPTICAL ACTIVITY
• The presence of asymmetrical carbon atoms causes
optical activity.
• When a beam of plane polarised light is passed
through a solution of carbohydrates, it will rotate the
light either to right or left.
• Depending on the rotation, molecules are :
Dextrorotatory (+/d)
Levorotatory (-/l)

21.
• Racemic mixture : Equimolar mixture of
optical isomers, has no net rotation.
• NOTE : D and L notation has no bearing with
the optical activity.
• D-glucose is dextrorotatory
• D-fructose is levorotatory.

22.
PROFESSOR JAROSLAV HEYROVSKY
• NOBEL PRIZE FOR CHEMISTRY 1959
• POLAROGRAPHIC ANALYSIS OF SUGARS

23.
EPIMERS
Sugars that differ only by the configuration
about one C atom are known as epimers of
one another.

24.
ANOMERISM
The cyclization of a monosaccharide renders the former
carbonyl carbon asymmetric.
The resulting pair of diastereomers are known as anomers and
the hemiacetal or hemiketal carbon is referred to as the
anomeric carbon.
In the α anomer, the OH substituent to the anomeric carbon
is on the opposite side of the sugar ring from the CH2OH
group at the chiral center that designates the D or L
configuration (C5 in hexoses).
The other anomer is known as the β form .

25.
MUTAROTATION
• The two anomers of D-glucose, as any pair of diastereomers,have different
physical and chemical properties.
• For example, the values of the specific optical rotation, for α-D-glucose
and β-D-glucose are, respectively,112.2° and 18.7°
• When either of these pure substances is dissolved in water, however, the
specific optical rotation of the solution slowly changes until it reaches an
equilibrium value of 52.7°. This phenomenon is known as mutarotation in
glucose, it results from the formation of an equilibrium mixture consisting
of 63.6% of the β anomer and 36.4% of the α anomer.

26.
Tautomerization or enolization
The process of shifting a hydrogen atom from one carbon atom to
another to produce enediols is known as tautomerisation.
Sugars possesing anomeric carbon atoms undergo tautomerisation in
alkaline solutions.
In mild alkaline conditions, glucose is converted to fructose and
mannose. The interconversion of sugars through a common enediol
form is called Lobry de Bruyn-Van Ekenstein transformation.
The enediols are highly reactive,hence sugars in alkaline solution are
powerful reducing agents.

27.
Reducing property sugars
• If the hydroxyl group on the anomeric carbon of a cyclized
sugar is not linked to another compound by a glycosidic bond,
the ring can open. The sugar can act as a reducing agent, and
is termed a reducing sugar. Such sugars can react with
chromogenic agents (for example, Benedict’s reagent or
Fehling’s solution) causing the reagent to be reduced and
colored, with the aldehyde group of the acyclic sugar
becoming oxidized.

28.
Reactions of monosaccharides
1. Reduction
2. Oxidation
3. Dehydration
4. Osazone formation
5. Ester formation

29.
Reduction
• When treated with reducing agents such as sodium
amalgam, the aldehyde or keto group is reduced to
corresponding alcohol.
Sugars Alcohols
Glucose Sorbitol
Galactose Dulcitol
Mannose Mannitol
Fructose Mannitol + sorbitol
Ribose Ribitol

30.
GLUCOSE SORBITOL

31.
OXIDATION
• Under mild oxidising condition, the carbonyl
(aldehyde) carbon is oxidised to the carboxyl
group and yield aldonic acids.

32.
• When aldehyde group is protected,oxidation of the
last carbon (C-6) of glucose , galactose, or mannose-
forms the corresponding uronic acid: glucuronic,
galacturonic, or mannuronic acid.

33.
• Under strong oxidation conditions (nitric oxide and
heat), both first and last carbon atoms are
simultaneously oxidised to form dicarboxylic acid :
saccharic acid.
• Glucose is oxidised to glucosaccharic acid

34.
Dehydration

35.
Osazone formation
• Reducing sugars + phenylhydrazine = Osazone
SUGAR OSAZONE
GLUCOSE/ FRUCTOSE/
MANNOSE
NEEDLE SHAPED CRYSTALS
MALTOSE SUNFLOWER SHAPED.
LACTOSE POWDER PUFF SHAPED

36.
Ester formation
• Hydroxyl group of sugars can be esterified to
form acetates, propionates,benzoates,
phosphates,etc.
• Glucose-6-phosphate and glucose -1-
phosphate are intermediates of glucose
metabolism

37.
Amino sugars
• Amino groups substitute hydroxyl group to
form amino sugars.
• Amino group is added to C2
• No reducing property
• No osazone formation.

38.
AMINO SUGARS PRESENT IN
GLUCOSAMINE HYALURONIC ACID, HEPARIN, BLOOD
GROUP SUBSTANCES.
GALACTOSAMINE CHONDROITIN OF CARTILAGE,BONE ,
TENDONS
MANNOSAMINE GLYCOPROTEINS
N-ACETYL GLUCOSAMINE , N- ACETYL
GLACTOSAMINE
GLYCOPROTEINS,
MUCOPOLYSACCHARIDES, CELL
MEMBRANE ANTIGENS.

39.
Deoxy sugars
• Oxygen of hydroxyl group may be removed to
form deoxy sugars
• Donot reduce
• Donot produce osazones

40.
Glycosides
• When the hemiacetal group (hydroxyl group of the
anomeric carbon) of a monosaccharide is condensed
with an alcohol or phenol group,it is called a glycoside.
• The non carbohydrate group is called aglycone.
• Donot reduce Benedict’s reagent.
• Enzyme hydrolysis can be used to distinguish between
α and β glycosides by maltase and emulsin.

41.
Glycosides Importance
Glucovanillin ( vanillin –D- glucose) Vanilla flavour
Cardiac glycosides (steroidal glycosides) Stimulate muscle contraction
Streptomycin Anti Tb drug
Ouabain Blocks sodium potassium ATPase pump.
Phlorhizin Renal damage in experimental animals
Plant indican Stain

42.
DISACCHARIDES
• Disaccharides (such as maltose,lactose and
sucrose) consist of two monosaccharide
joined covalently by an O-glycosidic bond,
which is formed when a hydroxyl group of one
sugar reacts with the anomeric carbon of the
other.

43.
Maltose
• Two glucose units are joined by an a -1,4 glycosidic
linkage.
• Maltose comes from the hydrolysis of starch and is
in turn hydrolyzed to glucose by maltase.

44.
Isomaltose
• 2 glucose units linked by α-1,6 linkage.

45.
Isomaltose contd.
• Produced by partial hydrolysis of glycogen and
starch.
• Oligo-1,6-glucosidase present in intestinal
juice hydrolyse isomaltose into glucose units.

46.
Lactose
• Lactose, the disaccharide of milk, consists of
galactose joined to glucose by a β-1,4-glycosidic
linkage.

47.
Sucrose
• Sucrose (common table sugar) is obtained
commercially from cane or beet.
• The anomeric carbon atoms of a glucose unit and a
fructose unit are joined in this disaccharide by α-1,2
glycosidic linkage .

48.
Sucrose contd.
• Non reducing.
• No osazone formation.
• Sucrose can be cleaved into its component
monosaccharides by the enzyme sucrase/ invertase.
• Invert sugar : equimolecular mixture of glucose and
fructose formed on hydrolysis.

49.
POLYSACCHARIDES
• Polysaccharides also called glycans.
• Large polymeric oligosaccharides, formed by
the linkage of multiple monosaccharides, are
called polysaccharides.
• Homopolysaccharides.
• Heteropolysaccharides .

50.
Homopolysaccharides
Starch
Glycogen
Cellulose
Inulin
Dextrans
Chitin

51.
STARCH
• The nutritional reservoir in plants.
• Amylose, the unbranched type of starch,consists of
glucose residues in α -1,4 linkage.
• Amylopectin, the branched form, has about 1 a -1,6
linkage per 30 a -1,4 linkages, in similar fashion to
glycogen except for its lower degree of branching.

52.
• Both amylopectin and amylose are rapidly hydrolyzed by α-amylase, an
enzyme secreted by the salivary glands and the pancreas.
• HYDROLYSIS
• In presence of mild acids smaller and smaller fragments are produced.
• Hydrolysis over a short time produces amylodextrin : gives violet colour
with iodine and is non reducing.
• Further hydrolysis produces erythrodextrins which give red colour with
iodine and mildly reduce benedict’s solution
• Achrodextrins (No colour with iodine, but powerfully reducing)
• ON CONTINUED hydrolysis forms maltose (no colour with iodine, but
powerfully reducing )

53.
GLYCOGEN
• Glycogen is the main storage polysaccharide
of animal cells.

54.
• Stored in liver(7% of wet weight) and skeletal
muscle.
• Glycogenin is a primer protein present in
innermost core of glycogen.
• More branched than amylopectin.

55.
DIFFERENCE BETWEEN STARCH AND
GLYCOGEN
Starch Glycogen
Plants Animals
Stored in tubers,grains,
legumes.
Stored in liver and muscle cells
Less branched More branched
Glycogenin absent Glycogenin present
Molecular weight of 10 – 1000
kdal
1000-5000 kdal
Blue and violet complexes
with iodine
Red violet complex with
iodine

56.
CELLULOSE
• Cellulose, the other major polysaccharide of
glucose found in plants, serves a structural rather
than a nutritional role.
• One of the most abundant organic compounds in
the biosphere.
• Constitutes much of the mass of wood and cotton
is almost pure cellulose.

57.
• Glucose residues have the β configuration .
• The glucose residues in cellulose are linked by
(β1,4)glycosidic bonds.

58.
INULIN
• Long chain homoglycan composed of D-fructose
units with repeating β-1,2 linkages.
• Present in bulbs of dahlia, onion, garlic.
• Used to find : renal clearance and glomerular
filtration rate.

59.
DEXTRANS
• Dextrans are bacterial and yeast polysaccharides
made up of (α1,6)-linked poly-D-glucose; all have
(α1,3) branches, and some also have (α1,2) or (α1,4)
branches.
• Used for hypovolemic shock as plasma expanders.

60.
CHITIN
• Linear homopolysaccharide composed of N-
acetylglucosamine residues in (β1,4) Iinkage

61.
SUMMARY
• Carbohydrates are polyhydroxy aldehydes or ketones, or substances that
yield such compounds on hydrolysis.
• Sugars have large numbers of stereoisomers because they contain several
assymetreic carbon atoms.
• Glucose is the only monosaccharide that exist in body in free form.
• Lactose and sucrose are important dietary dissacharides.
• Starch , cellulose and glycogen are important homoglucan polymers.
• Dextran is used as a plasma expander.

62.
REFERENCES
1. TEXTBOOK OF BIOCHEMISTRY FOR MEDICAL STUDENTS, 7TH Ed., DM VASUDEVAN,
SREEKUMARI
2. BIOCHEMISTRY, U.SATYANARAYANA, U.CHAKRAPANI, 4TH Ed.
3. LEHNINGER PRINCIPLES OF BIOCHEMISTRY,DAVID L. NELSON, MICHAEL M. COX, 5TH Ed.
4. BIOCHEMISTRY 5TH Ed. JEREMY M. BERG, JOHN L. TYMOCZKO,LUBERT STRYER
5. LIPPINCOTT’S ILLUSTRATED REVIEWS- BIOCHEMISTRY, 5TH Ed.
6. BIOCHEMISTRY, DEBAJYOTI DAS,14th Ed.
7. BIOCHEMISTRY,DONALD VOET,JUDITH G. VOET, 4TH Ed.
8. WIKIPEDIA