This document provides information about carbohydrates. It discusses that carbohydrates are the most abundant organic molecules in nature and an important source of energy for cells. Carbohydrates can also act as structural components and be involved in cell membranes, surface antigens, and extracellular substances. The document further describes different types of carbohydrates including monosaccharides, disaccharides, and polysaccharides. It provides examples and characteristics of important carbohydrates such as glucose, fructose, sucrose, lactose, and glycogen. Reaction and derivatives of monosaccharides are also summarized.

1. DEPARTMENT OF VETERINARY BIOCHEMISTRY
CARBOHYDRATES
SUBMITTED BY ;-
BHAGRAJ GODARA
M.V.Sc 1st year
RAJASTHAN UNIVERSITY OF VETERINARY AND ANIMAL SCIENCES,BIKANER

2. Carbohydrates
• The most abundant organic molecules in nature
• Provide a significant fraction of the energy in the diet of most organisms
• Important source of energy for cells
• Can act as a storage form of energy
• Can be structural components of many organisms
• Can be cell-membrane components mediating intercellular communication
• Can be cell-surface antigens
• Can be part of the body’s extracellular ground substance
• Can be associated with proteins and lipids
• Part of RNA, DNA, and several coenzymes (NAD+, NADP+, FAD, CoA)

3. CARBOHYDRATES
Polyhydroxy aldehydes or ketones or substances that yield these compounds on
hydrolysis
CHO
|
H- C - OH
|
CH2OH
CH2OH
|
C = O
|
CH2OH
Glyceraldehyde Dihydroxyacetone
Aldehyde
group Keto
group
Carbohydrate with an aldehyde group: Aldose
Carbohydrate with a ketone group : Ketose
Empirical formula of many simpler carbohydrates: (CH2O)n (hence the
name hydrate of carbon)

4. Monosaccharides
Polyhydroxy aldehydes or ketones that can’t easily be further hydrolyzed
“Simple sugars”
Number of carbons Name Example
3 Trioses Glyceraldehyde
4 Tetroses Erythrose
5 Pentoses Ribose
6 Hexoses Glucose, Fructose
7 Heptoses Sedoheptulose
9 Nonoses Neuraminic acid

5. Oligosaccharides
• Hydrolyzable polymers of 2-6 monosaccharides
• Disaccharides composed of 2 monosaccharides
Examples: Sucrose, Lactose
Polysaccharides
Hydrolyzable polymers of > 6 monosaccharides
Homopolysaccharides: polymer of a single type of monosaccharides
Examples: Glycogen, Cellulose
Heteropolysaccharides: polymer of at least 2 types of monosaccharide
Example: Glucosaminoglycans

6. Monosaccharides
• Number of carbons Name Example
• 3 Trioses Glyceraldehyde
• 4 Tetroses Erythrose
• 5 Pentoses Ribose
• 6 Hexoses Glucose, Fructose
• 7 Heptoses Sedoheptulose
• 9 Nonoses Neuraminic acid

7. Common Monosaccharides

8. Aldose sugars
C
C
CH2OH
OH)n(H
O
H
Aldose
C
C
CH2OH
OHH
O
H
Aldotriose
n = 1
C
CH2OH
OHH
C O
H
C OHH
Aldotetrose
n = 2
C
CH2OH
OHH
C O
H
C OHH
C OHH
Aldopentose
n = 3
C O
H
C OHH
C OHH
CH OH
C
CH2OH
OHH
Aldohexose
n = 4

9. Ketose sugars
C
C
CH2OH
OH)n(H
O
CH2OH
Ketose
CH2OH
C O
CH2OH
Ketotriose
n = 0
CH2OH
C O
C OHH
CH2OH
Ketotetrose
n = 1
C OHH
CH2OH
CH2OH
C O
C OHH
Ketopentose
n = 2
C OHH
CH2OH
CH2OH
C O
C OHH
OHH
Ketohexose
n = 3

10. Conformational formulas
The structure of Glucose can be represented in three ways:
Straight Chain Form Haworth Projection Chair Form

11. D & L Stereoisomers
Those monosaccharides that are of physiological significance exist in
the D-configuration, where the hydroxyl group is on the right side .
The mirror-image, called enantiomers, are in the L-configuration.
They are related to glyceraldehyde which exists in two isomers D and L
Monosaccharides can exist in either of two configurations, as
determined by the orientation of the hydroxyl group about the
asymmetric carbon farthest from the carbonyl group.
e,g D & L form of glucose is determine by carbon 5.

14. L and D Enantiomers
It also called mirror images or Optical Isomers:

15. L and D Enantiomers

16. Epimers
Two monosaccharide that differ from each other by position of OH group on one
carbon. ( eg. carbon 2 and 4 of glucose).
Mannose Glucose Galactose

17. Formation of Hemiacetals and Hemiketals
An aldehyde or ketone can react with an alcohol in a 1:1 ratio to yield a hemiacetal or hemiketal,
respectively, creating a new chiral center at the carbonyl carbon. Substitution of a second alcohol
molecule produces an acetal or ketal. When the second alcohol is part of another sugar molecule,
the bond produced is a glycosidic bond (p. 245).

18. Pyranose and Furanose ring
Monosaccharide with 5 or 6 carbon
atoms tend to cyclyze in solution.
This terminology indicate that the
ring structure of monosaccharide is
similar to either pyran or furan

19. α- and β anomers
Isomers that differ on the position of OH group around anomeric carbon
(which was carbonyl carbon) when the ring is formed.

20. Cyclization
Formation of the two cyclic forms of D-
glucose. Reaction
between the aldehyde group at C-1 and
the hydroxyl group at
C-5 forms a hemiacetal linkage,
producing either of two stereoisomers,
the and anomers, which differ only in
the stereochemistry
around the hemiacetal carbon. The
interconversion of and anomers
is called mutarotation.

21. Glycosidic bonds
the Iinkages between the carbon atoms and the status of the anomeric
carbon (α or β). For instance, lactose-which is formed by a bond
between C1 of β-D-galactopyranosyl-(1→4)- D-glucopyranose
Lactose: β-D-galactopyranosyl-(1→4)- D-glucopyranose
Maltose: α-D-glucopyranosyl-(1→4)- D-glucopyranose
Isomaltose: α-D-glucopyranosyl-(1→6)- D-glucopyranose
Sucrose: α-D-glucopyranosyl-(1→2)- D-fructofuranose

22. Physiologieally important glycosides
1. Glucovanillin (vanillin-D-glucoside)is a natural substance that
imparts vanilla flavour.
2. Cardiac glycosides( steroidal glycosides:) Digoxin and digitoxin
contain the aglycone steroid and they stimulate muscle contraction.
3. Streptomycin, an antibiotic used in the Treatment of tuberculosisi s a
glycoside.
4. Ouabain inhibits Na+ - K+ ATPase and blocks the active transport of
Na+.

23. REACTIONS OF MONOSACCHARIDES
• Tautomerization or enolization
• Reducing Properties
• Oxidation
• Reduction
• Dehydration
• Osazone formation

24. Tautomerization or enolization
• The process of shifting a hydrogen atom
from one carbon atom to another to
produce enediols is known as
tautomerization.
• Sugars possessing anomeric carbon atom
undergo tautomerization
in alkaline solutions.
• When glucose is kept in alkaline solution
for several hours,it undergoes isomerization
to form D-fructose and D-mannose. This
reaction known as the Lobry de Bruyn-
von Ekenstein transformation -results in
the formation of a common intermediate-
namely enediol-for all the three sugars,

25. Reducing Properties
• The sugars are classified as reducing or nonreducing.
• The reducing property is attributed to the free aldehyde or keto group of
anomeric carbon.
• ln the laboratory, many tests are employed to identify the reducing action of
sugars. These include Benedict's test, Fehling's test, Barfoed’s tesf etc.
• The reduction is much more efficient in the alkaline medium than in the
acid medium.
• The enediol forms or sugars
reduce cupric ions (Cu2+) of
copper sulphate to cuprous ions
(Cu+), which form a yellow
precipitate of cuprous hydroxide
or a red precipitate of cuprous
oxide as shown next

26. Oxidation
Depending on the oxidizing agent used, the terminal aldehyde (or keto)
or the terminal alcohol or both the groups may be oxidized. For instance,
consider glucose :
1. Oxidation of aldehyde group (CHO ------>
COOH) resultsi n the formation of gluconic acid.
2. Oxidation of terminal alcohol group
(CH2OH ------+C OOH) leads to the production of glucuronic acid.

27. Reduction
When treated with reducing agents such as sodium amalgam, the
aldehyde or keto group of monosaccharide is reduced to corresponding
alcohol, as indicated by the general formula :
The important monosaccharides and their correspondinga lcoholsa re
given below.
D-Glucose------- D- Sorbitol
D-Galactose ------ D-Dulcitol
D-Mannose ------ D-Mannitol
D-Fructose --------D-Mannitol + D-Sorbitol
D-Ribose ---------- D-Ribitol

28. Dehydration
When treated with concentrated sulfuric acid,
monosaccharides undergo dehydration with an
elimination of 3 water molecules. Thus
hexoses give hydroxy methyl furfural while
pentoses give furfural on dehydration.
These furfurals can condense with phenolic
compounds (a-naphthol) to form coloured
products. This is the chemical basis of the
popular Molisch test. In case of oligo- and
polysaccharides they are first hydrolysed to
monosaccharide by acid, and this is followed
by dehydration.

29. Osazone formation
Phenylhydrazine in acetic acid, when
boiled with reducing sugars, forms
osazones.the first two carbons (C1 and C2)
are involved in osazone formation. The
sugars that differ in their configuration on
these two carbons give the same type of
osazones, since the difference is masked
by binding with phenylhydrazine Thus
glucose, fructose and mannose give the
same type (needle-
shaped)osazones.Reducing disaccharides
also give osazones maltose sunflower-
shaped, and lactose powderpuff shaped.

30. DERIVATIVES OF MONOSACCHARIDES
• Sugar acids
• Sugar Alcohols
• Alditols
• Amino sugars
• Deoxy sugars
• L-Ascorbic acids(vitamin C

31. Sugar acids
Oxidation of aldehyde or primary alcohol group in monosaccharide
results in sugar acids.Gluconic acid is produced from glucose by
oxidation of aldehyde (C1 group) whereas glucuronic acid is formed
when primary alcohol group (C6) is oxidized.
They are produced by reduction of aldoses or ketoses For instance,
D-Glucose------- D- Sorbitol
D-Galactose ------ D-Dulcitol
D-Mannose ------ D-Mannitol
D-Fructose --------D-Mannitol + D-Sorbitol
D-Ribose ---------- D-Ribitol
Sugar alcohols (polyols) :

32. Alditols
The monosaccharides, on reduction, yield polyhydroxy alcohols, known
as alditols. Ribitol is a constituent of flavin coenzymes; glycerol and
myo-inositol are components of lipids. Xylitol is a sweetener used in
sugar lesgsums and candies
This is a water-soluble vitamin, the structure of which closely
resemblesth at of a monosaccharide.
L-Ascorbic acid (vitamin C)

33. Amino sugars
When one or more hydroxyl groups of the monosaccharides are replaced by
amino groups, the products formed are amino sugars e.g. D-glucosamine, D-
galactosamine. They are present as constituents
of heteropolysaccharides
The amino groups of amino sugars are sometimes acetylated e.g. N-acetyl D-
glucosamine.
N-Acetylneuraminic acid (NANA) is a derivative of N-acetyl mannose and
pyruvic acid.
It is an important constituent of glycoproteins and glycolipids. The term sialic
acid is used to include NANA and its other derivatives. Certain antibiotics
contain amino sugars which may be involved in the antibiotic activity
e.g. erythromycin

34. Deoxysugars
These are the sugars that contain one oxygen less than that present in the
parent molecule. The groups -CHOH and -CH2OH become -CH2 and -
CH3 due to the absence of oxygen. D-2-Deoxyriboseis the most
important deoxy sugar since it is a structural constituent of DNA (in
contrast to D-ribose in RNA).

35. Disaccharides
Disaccharides (such as maltose, lactose, and sucrose) consist of two
monosaccharides joined covalently by an glycosidic bond, which is
formed when a hydroxyl group of one sugar reacts with the anomeric
carbon of the other.
They are crystalline,water soluble and sweet to taste
TheDisaccharides are of two types
1. Reducing disaccharides with free aldehyde or keto group e.g.
maltose, lactose.
2. Non-reducing disaccharides with no free aldehyde or keto group e.g.
sucrose, trehalose

36. Maltose
Maltose is composed of two α-D-glucose units held together by α (1-4)
glycosidic bond. The free aldehyde group present on C1 of second
Glucose answers the reducing reactions ,besides the osazone formations
(sunflower-shaped).
Maltose can be hydrolysed by dilute acid or the enzyme maltase to
liberate two molecules of α -D-glucose.
ln isomaltose, the glucose units are held together by α(1 - 6) glycosidic
linkage.
Cellobiose is another disaccharide, identical in structure with maltose,
except that the former has β (1-4) glycosidic linkage. Cellobiose is
formed during the hydrolysis of cellulose

38. LACTOSE
Lactose is more commonly known as milk sugar
since it is the disaccharide found in milk.
Lactose is composed of β-D-galactose and β–
D-glucose held together by β (1-4) glycosidic
bond.
The anomeric carbon of C1 glucose is free,
hence lactose exhibits reducing properties and
Forms osazones(powder-puff or hedgehog
shape).
Lactose of milk is the most important
carbohydrate in the nutrition of young
mammals. It is hydrolysed by the intestinal
enzyme lactase to glucose and galactose.

39. SUCROSE
Sucrose(cane sugar) is the sugar of
commerce, mostly produced by sugar
cane and sugar beets. Sucrose is made
up of α-D-glucose and β-D-fructose.
The two monosaccharides Are held
together by a glycosidic bond (α1-β
2),between C1 of D-glucose and C2 of β
-D-fructose. The reducing groups of
glucose and fructose are involved in
glycosidic bond, hence sucrose is a non-
reducing sugar, and it cannot form
osazone, It is the major carbohydrate
produced in photosynthesis.

41. Polysaccharides
• Polysaccharide(or simply glycans) consist of repeat units of
monosaccharides or their derivatives, held together by glycosidic bonds.
They are primarily concerned with two important functions-structural an d
storage of energy
• polymers of medium to high molecular weight. Polysaccharides, also called
glycans, differ from each other in the identity of their recurring
monosaccharide units, in the length of their chains, in the types of bonds
linking the units, and in the degree of branching.
• Homopolysaccharides contain only a single type of monomer;
heteropolysaccharides contain two or more different kinds Some
homopolysaccharides serve as storage forms of monosaccharides that are
used as fuels(starch and glycogen),Other homopolysaccharides (cellulose
and chitin) serve as structural elements in plant cellwalls and animal
exoskeletons.

42. Homo- and heteropolysaccharides. Polysaccharides may be composed of one, two, or several
different monosaccharides, in straight or branched chains of varying length.

43. STARCH
Starch is the carbohydrate reserve of plants which is the most important
dietary source for higher animals, including man. High content of starch is
found in cereals, roots, tubers, vegetables etc. Starch is a homopolymer
composed of D-glucose units held by a glycosidic bonds. lt is known as
glucosan or glucan.
Starch contains two types of glucose polymer, amylose and amylopectin.The
former consists of long, unbranched chains of D-glucose residues connected
by (α 1-4) linkages. Such chains vary in molecularweight from a few
thousand to more than a million.
Amylopectin also has a high molecular weight (upto 100 million) but unlike
amylose is highly branched.The glycosidic linkages joining successive
glucose residues in amylopectin chains are (α 1-4); the branch points
(occurring every 24 to 30 residues) are (α1-6) linkages.

45. Dextrans
Dextrans breakdown product of starch (amylase) are bacterial and yeast
polysaccharidesmade up of (α1-6)-linked poly-D-glucose; all have (α1-
3) branches, and some also have (α1-2) or (α 1-4) branches. Dental
plaque, formed by bacteria growing on the surface of teeth, is rich in
dextrans. Synthetic dextrans are used in several commercial products
(Sephadex) that serve in the fractionation of proteins by size-exclusion
chromatography.
The dextrans in these products are chemically cross-linked to form
insoluble materials of various porosities, admitting macromolecules of
various sizes.

46. INULIN
Inulin is a polymer of fructose i.e., fructosan. It occurs in dahlia bulbs,
garlic, onion etc. lt is a low molecular weight (around 5,000)
polysaccharide easily soluble in water. Inulin is not utilized by the body.
lt is used for assessing kidney function through measurement of
glomerular filtration rate (GFR).

47. Glycogen
Glycogen is the main storage polysaccharide of animal cells.referred as
animal starch, Like amylopectin, glycogen is a polymer of (α1-4)-linked
subunits of glucose, with (α1-6)-linked branches, but glycogen is more
extensively branched (on average, every 8 to 12 residues) and more
compact than starch. Glycogen is especially abundant in the liver where
it may constitute as much as 7% of the wet weight; it is also present in
skeletal muscle. In hepatocytes glycogen is found in large granules,
which are themselves clusters of smaller granules composed of single,
highly branched glycogen molecules with an average molecular weight
of several million. Such glycogen granules also contain, in tightly
bound form, the enzymes responsible for the synthesis and degradation
of glycogen. en iespecially abundant in the liver

48. Cellulose
• Cellulose is composed of β -D-glucose units linked by β(1- 4) glycosidic
bonds, Cellulose cannot be digested by mammals including man-due to lack
of the enzyme that cleaves β –glycosidec bonds (α amylase break α bonds
only). Certain ruminants and herbivorous animals contain microorganismis
in the gut which produce enzymes that can cleave β -glycosidic bonds.
• Hydrolysis of cellulose yields a disaccharide cellobiose, followed by β –D-
glucose.
• Cellulose, though not digested, has great importance in human nutrition. lt
is a major constituento l fiber, the non-digestable carbohydrate. The
functions of dietary fiber include decreasing the absorption of glucose and
Cholesterol from the intestine, besides increasing the bulk of feces.

49. Cellulose Structure
The structure of cellulose. (a) Two units of
a cellulose chain; the D-glucose residues
are in (1n4) linkage. The rigid chair
structures can rotate relative to one
another. (b) Scale drawing of segments of
two parallel cellulose chains, showing the
conformation of the D-glucose residues
and the hydrogen-bond cross-links. In the
hexose unit at the lower left, all hydrogen
atoms are shown; in the other three hexose
units, the hydrogens attached to carbon
have been omitted for clarity as they do
not participate in hydrogen bonding.

50. Chitin
Chitin is composed of N-acetyl D-glucosamine units held together by β
(1-4) glycosidic bonds.
• lt is a structural polysaccharide found in the exoskeleton of some
invertebrates e.g. inscts, crustaceans and and is probably the second
most abundant polysaccharide, next to cellulose, in nature.
A short segment of chitin,a homopolymer of N-acetyl-D-glucosamine units in β (1-4) linkage.

51. Heteropolysaccrides
heteropolysaccharides contain two or more different kinds of
monosaccharides
MUCOPOLYSACCHARIDES are heteroglycans madeup of repeating
units of sugar derivatives namely
amino sugars and uronic acids. These are more commonly known as
glycosaminoglycans (GAG). Acetylated amino groups, besides sulfate and
carboxyl groups are generally present in GAG structure. The presence of
sulfate and carboxyl groups contributes to acidity of the molecules, making
them acid mucopolysaccharides. Some of the mucopolysaccharides are found
in combination with proteins to form mucoproteins or mucoids or
proteoglycans
Mucoproteins(mucoid or proteoglycans) may contain up to 95% carbohydrate
and 5% protein.

52. MUCOPOLYSACCARIDES
• HYALURONIC ACID
• CHODROTIN 4-SULFATE
• HEPARIN
• DERMATIN SULFATE
• KERATIN SULFATE

54. Glycoconjugates
• the informational carbohydrate is covalently joined to a protein or a
lipid to form a glycoconjugate, which is the biologically active
molecule.
• Specific carbohydratecontaining molecules act in cell-cell recognition
and adhesion, cell migration during development, blood clotting, the
immune response, and wound healing, to name but a few of their
many roles
Glycolipids are membrane lipids in which the hydrophilic head
groups are oligosaccharides, which, as in glycoproteins, act as
specific sites for recognition by carbohydrate- binding proteins

55. Proteoglycans
Proteoglycans are macromolecules of the cell surface or extracellular
matrix in which one or more glycosaminoglycan chains are joined
covalently to a membrane protein or a secreted protein. The
glycosaminoglycan moiety commonly forms the greater fraction (by
mass) of the proteoglycan molecule, dominates the structure, and is
often the main site of biological activity. In many cases the biological
activity is the provision of multiple binding sites, rich in opportunities
for hydrogen bonding and electrostatic interactions with other proteins
of the cell surface or the extracellular matrix. Proteoglycans are major
components of connective tissue such as cartilage, in which their many
noncovalent interactions with other proteoglycans, proteins, and
glycosaminoglycans provide strength and resilience.

56. Glycoproteins
Glycoproteins have one or several oligosaccharides of varying
complexity joined covalently to a protein. They are found on the outer
face of the plasma membrane, in the extracellular matrix, and in the
blood.
Inside cells they are found in specific organelles such as Golgi
complexes, secretory granules, and lysosomes. The oligosaccharide
portions of glycoproteins are less monotonous than the
glycosaminoglycan chains of proteoglycans; they are rich in
information, forming highly specific sites for recognition and high
affinity binding by other proteins.

58. Antifreeze glycoproteins
The Antarctic fish live below -2*C, a temperature at which the blood
would Freeze. lt is now known that these fish contain antifreeze
glycogtratein which lower the freezing point of water and interfere with
the crystal formation of ice.
Antifreeze giycoproteins consist of 50 repeating units of the tripeptide,
alanine-alanine-threonine.
Each threonine residue is bound to β -galactosyl (1-3) α( N-acetygl
alactosamine

59. The Sugar Code
Carbohydrates as Informational Molecules: Monosaccharides can be
assembled into an almost limitless variety of oligosaccharides, which
differ in the stereochemistry and position of glycosidic bonds, the type
and orientation of substituent groups, and the number and type of
branches. Oligosaccharides are far more information-dense than nucleic
acids or proteins.
Lectins, proteins with highly specific carbohydrate-binding domains,
are commonlyfound on the outer surface of cells, wherethey initiate
interaction with other cells. Invertebrates, oligosaccharide tags “read”
by lectinsgovern the rate of degradation of certain peptidehormones,
circulating proteins, and blood cells

60. • The adhesion of bacterial and viral pathogens to their animal-cell
targets occurs through binding of lectins in the pathogens to
oligosaccharides in the target cell surface. Lectins are also present
inside cells, where they mediate intracellular protein targeting.
• X-ray crystallography of lectin-sugar complexes shows the detailed
complementarity between the two molecules, which accounts for the
strength and specificity of their interactions with carbohydrates.
• Selectins are plasma membrane lectins that bind carbohydrate chains
in the extracellular matrix or on the surfaces of other cells, thereby
mediating the flow of information between cell and matrix or between
cells.