Dr : Abdel naser Badawy
‐ Carbohydrates are organic molecules found in nature,
constituting one of the four major classes of biomolecules.
‐‐ The other three are proteins, nucleic acids and lipids.
-- Saccharides (saccharo is Greek for ―sugar)
• Carbohydrates are aldehyde or
ketone compounds with multiple
• The basic molecular formula
(C.H2O)n where n = 3 or more.
• The term ―carbohydrate comes
from the observation that when you
heat sugars, you get carbon and
water (hence, hydrate of carbon).
They are classified according to the number of structural units into:
1‐Monosaccharides= They are the simplest carbohydrates that can not
be hydrolysed into simpler units.
2‐ Disaccharides= produce 2 molecules of monosaccharide on
3‐ Oligosaccharides= produce three to ten monosaccharide units on
4‐ Polysaccharides= : produce more than 10 monosaccharide units on
• * Def : They are the simplest
carbohydrate unites which can not be
hydrolyzed to a simpler form
• * General formula: (CH2O)n n≥3
• 1- According to active group in
– If monosaccharide contains
aldehyde group (CHO) → it's
– And if contain ketone group
(c=o) → it's called
According to the number of carbon atoms (n):‐2
If sugar contains
3 carbons → it's called triose, 4c→ tetrose 5c→ pentose
6c→ hexose 7c→ heptose
Three Carbon Four Carbon
By combining the two methods , we find that:-3
The structure of glucose can be represented in one of the
1.The straight – chain (open ‐ chain) structural formula :
Aldohexose can account for some of the properties of glucose, but
can not explain some reaction
2. The cyclic structure accounts for the remainder of the chemical
properties of glucose. This cyclic structure can be represented in two
a. Fischer projection formula :where the aldehyde group reacts with
an alcohol group on the same sugar to form a hemiacetal ring.
H – C – OH
HO – C – H
H – C – OH
H – C
H – C – OH
HO –C – H
H – C – OH
H – C
b. Haworth formula:
Where the cyclic structure is represented in pyranose (six – membered) and
furanose (five – membered) rings resembling pyran and furan rings.
Here oH and H written above and below instead of Right and left
so what is on Right → below left → above
except last carbon (which close the ring) in which
left →below Right →above
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
Hemiacetals or Hemiketals
:c) Boat and chair forms
represents the three dimensional configuration of sugar in nature.
carbon):chiralcarbon atom (
• It is that carbon atom attached
to four different groups or
• Formation of a ring results in the
creation of an anomeric carbon
at carbon 1 of an aldose or at
carbon 2 of a ketose.
• If the oxygen on the anomeric
carbon (the carbonyl group) of a
sugar is not attached to any
other structure, that sugar is a
• Only the state of the oxygen on
the anomeric carbon determines
if the sugar is reducing or
nonreducing—the other hydroxyl
groups on the molecule are not
• A reducing sugar can
react with chemical
solution) and reduce
component, with the
Any compound having one or more asymmetric carbon atom
shows two properties:
1. Optical activity.
• Def. It is the ability of the compound to rotate
plane polarized light to the right or to the left.
• If the compound rotates plane polarized light
to the right, it is called dextrorotatory, d or
• If it rotates plane polarized light to the left, it
is called levorotatory, l or (-).
• The direction of rotation is independent
of the stereochemistry
• of the sugar, so it may be designated
D(−), D(+), L(−), or L(+).
• For example, the naturally occurring
form of fructose is the D(−) isomer.
•• dextrorotatorydextrorotatory sugar (d or +):sugar (d or +):
glucose,glucose, galactosegalactose and starchand starch
•• levorotatorylevorotatory sugar (l orsugar (l or --):): fructosefructose
and invert sugarand invert sugar..
Compound that have the same structural formula but differ in
spatial configuration are known as stereoisomers and the
phenomenon is called stereoisomerism.
The number of possible isomers of a compound depends on the
number of asymmetric carbon atoms (n) and is equal to 2n.
Glucose, with four asymmetric carbon atoms, has 16 isomers.
• The more important types of isomers
– D and L isomers,
– pyranose and furanose ring structures,
– alpha and beta anomers,
– epimers and
– aldose-ketose isomers.
Are compounds which have the same molecularAre compounds which have the same molecular
weight, same percentage composition, and differweight, same percentage composition, and differ
in their physical and chemical properties.in their physical and chemical properties.
-- StereoisomersStereoisomers: are compounds that have the: are compounds that have the
same structural formula but differ in spatialsame structural formula but differ in spatial
configuration (arrangement of atoms and groupsconfiguration (arrangement of atoms and groups
of atoms in space around the asymmetricof atoms in space around the asymmetric
carbon(scarbon(s) i.e. different configuration).) i.e. different configuration).
1. D and L isomers
• A special type of
isomerism is found in
the pairs of structures
that are mirror image of
• These mirror images
are called enantiomers
and the two members of
the pair are designated
as a D and an L-sugar.
• A monosaccharide is
designated D if the
hydroxyl group on the
prelast carbon is drawn to
the right as in D-
glyceraldehyde and L if the
hydroxyl group on the
asymmetric carbon is
drawn to the left as in L-
‐ The majority of the sugars in humans are D‐sugars.
‐ Two exceptions are L‐fucose (in glycoproleins) and L‐iduronic
ring structures: furanoseand Pyranose2.
The monosaccharides are either pyran (a six‐membered
ring) or furan (a five‐membered ring).
For glucose in solution, more than 99% is in the pyranose form.
:anomers3. Alpha and beta
The ring structure of an aldose is a hemiacetal, since it is
formed by combination of an aldehyde and an alcohol group.
Similarly, the ring structure of a ketose is a hemiketal. The cyclic
structure is retained in solution, but isomerism (C6H12O6) occurs
about position 1, the carbonyl or anomeric carbon atom, to give
a mixture of α‐glucopyranose (38%) and β‐glucopyranose
• The cyclic α and β anomers of a sugar in
solution are in equilibrium with each other,
and can be spontaneously interconverted
(a process called mutarotation)
Isomers differing as a result of variations in configuration of
the OH and H on carbon atoms 2, 3, and 4 of glucose are known
as epimers. Biologically, the most important epimers of
(C6H12O6) glucose are mannose and galactose, formed by
epimerization at carbons 2 and 4, respectively.
Epimers of glucose
D- glucose D- galactose
Epimer at C4
Epimer at C2
Fructose has the same molecular formula as glucose
(C6H12O6) but differs in its structural formula, since there is keto
group in position 2, the anomeric carbon of fructose, whereas
there is aldehyde group in position 1, the anomeric carbon of
Are Physiologically Important:MonosaccharidesMany
xylose, ribuloseribose, e.g:Pentoses1
, fructose, mannosegalactoseglucose, : Hexoses‐2
) are formed as metabolic sedoheptulose(carbon sugar ‐seven‐3
intermediates in the pentose phosphate pathway.
g carboxylic acid derivatives of glucose are important, includin‐4
formation and in glucuronide(for glucuronate‐Da.
acid pathway)theuronic(an intermediate in gulonate‐Lc.
Lack an Oxygen Atom =Deoxy sugars are those in which a hydroxyl
group has been replaced by hydrogen. Examples:
a. deoxyribose in DNA.
b. L‐fucose occurs in glycoproteins.
c. 2‐deoxyglucose is used experimentally as an inhibitor of glucose
):Hexosamines2. Amino Sugars (
Are compounds in which OH at C2 is replaced by NH2
1. D‐glucosamine, a constituent of hyaluronic acid ,
2. D‐galactosamine(chondrosamine), a constituent of chondroitin;
3. Several antibiotics (eg, erythromycin) contain amino sugars
believed to be important for their antibiotic activity
1.1. Produced by oxidation ofProduced by oxidation of
carbonyl carbon to carboxyliccarbonyl carbon to carboxylic
2.2. Or by oxidation of last hydroxylOr by oxidation of last hydroxyl
carbon to carboxylic group.carbon to carboxylic group.
3.3. Or by oxidation of both.Or by oxidation of both.
Conc. Nitric acid
• The hemiacetal and hemiketal forms of
monosaccharides can react with alcohols
to form acetal and ketal structures called
glycosides. The new carbon-oxygen bond
is called the glycosidic linkage.
The OH of anomeric carbon of monosaccharides can react with either:
1‐ Nitrogen of amines (The anomeric carbon atom of sugar can be
linked to the nitrogen atom of an amine by N‐ glycosidic bond) e.g OH
of ribose linked to nitrogen of nitrogenous base to form nucleotides.
OH of other-2
• A- May be carbohydrate (
Monosaccharides can be linked to
each other by O- glycosidic bonds to
form disaccharides, oligosaccharides
• b- May be non carbohydrate e.g
• The non carbohydrate component of
a glycoside is called aglycone.
O- and N-glycosides
• If the group on the non-
to which the sugar is
attached is an -OH
group, the structure is an
• All sugar-sugar
glycosidic bonds are O-
O- and N-glycosides
• If the group is an -NH2 ,
the structure is an N-
– purines and pyrimidines
(found in nucleic acids),
– aromatic rings (such as
those found in steroids and
– proteins (found in
Naming glycosidic bonds
• Glycosidic bonds
between sugars are
named according to
– numbers of the
connected carbons (1-4,
– position of the
group of the sugar
involved in the bond.
Naming glycosidic bonds
• this anomeric hydroxyl
group is in the α
linkage is an α-bond.
• If it is in the β
linkage is a β-bond.
Naming glycosidic bonds
• Lactose, for example, is
synthesized by forming a
glycosidic bond between carbon
1 of β-galactose and carbon 4 of
– The linkage is, therefore:
β(1 →4) glycosidic bond.
• Because the anomeric end of the
glucose residue is not involved in
the glycosidic linkage it (and,
therefore, lactose) remains a
Naming of O‐ glycosidic bond() carbohydrate and carbohydrate
‐ Glycosidic bonds between sugars are named according to:
1‐ The numbers of the connected carbons
2‐ The position of the anomeric hydroxyl group of the sugar.
If the anomeric hydroxyl group is in α configuration the link is α‐
bond and if it’s in β, the link is β‐ bond. Examples
In lactose β 1 of galactose bind to C4 of glucose by β 1 → 4
Examples of glycosides:
1‐ Disaccharides as maltose, lactose and sucrose
4‐Glycoproteins.(may be O‐ or N‐ glycosidic link)
5‐Nucleotides as ATP, GTP, UTP where aglycon is purine or
pyrimidine bases (N‐ glycosides)
The glycosides that are important in medicine
1. cardiac glycosides all contain steroids as the aglycone.
2. Other glycosides include antibiotics such as streptomycin.
‐ Disaccharide consists of two sugars joined by an O‐ glycosidic bond.
‐ The most abundant disaccharides are sucrose, lactose and maltose.
‐ Other disaccharides include isomaltose, cellobiose and trehalose.
‐The disaccharides can be classified into homo disaccharides and
‐A) Homo disaccharides: are formed of the same monosaccharide units
and include maltose, isomaltose, cellobiose and trehalose.
‐(B) Hetero disaccharides: are formed of different monosaccharide
units and include: sucrose, lactose.
It is formed of -galactose and -glucose linked by
Contain free anomeric carbon so reducing sugar
It may appear in urine in late pregnancy and during
H OH ..... H
H ..... OH
• α D-glucopyranose and
β D fructofuranose by α
1- 2 glycosidic bond
• No free aldehyde or
keton gp so non
• hydrolysed to glucose
and fructose by sucrase
• * Sucrose is
Maltose (malt sugar):Maltose (malt sugar):
It consists of 2It consists of 2 --glucose units linked byglucose units linked by
--1,41,4--glucosidic linkage,glucosidic linkage,
Contain free anomeric carbon so reducing sugar.
H OH ..... H
H ..... OH
It is formed of 2 -glucose units linked by -1,1-
glucosidic linkage. Not Contain free anomeric
carbon so non reducing sugar
Present in a highly toxic lipid extracted from
CH 2O H
Disaccharides Components Reduction
1- sucrose =
= beet sugar =
and β D
by α 1- 2
keton gp so
fructose by sucrase
* Sucrose is
2- Lactose (milk
β D galactose
and α D glucose.
by β 1-4
* It may appear in
urine in late
Disaccharides *Components Bond Reduction
1- Maltose 2αD-glucose α 1-4 glycosidic Contain free
4- Trehalose 2αD-glucose α 1-1 glycosidic Not Contain
carbon so non
• Oligosaccharides contain from 3 to 10
• Raffinose An oligosaccharide found in
peas and beans
‐ Polysaccharides consist of more than 10 monosaccharide units and /
or their derivatives
Classification According to structure:
1‐ Homo polysaccharides (Homo glycans): contain only one type of
E.g. starch, glycogen, dextrin, cellulose, inulin and chitin
2‐ Hetero polysaccharides: contain more than one type of
E.g. glycosaminoglycan, glycoprotein.
‐ is a homopolymer of glucose forming an α‐ glucosidic chain, called a
glucosan or glucan.
‐It is the most abundant dietary carbohydrate in cereals, potatoes,
legumes, and other vegetables.
‐The two main constituents are amylose (15–20%), which has a
nonbranching helical structure) and amylopectin
(80–85%), which consists of branched chains composed of 24–30
glucose residues united by 1 → 4linkages in the chains and by 1 → 6
linkages at the branch points.
Are intermediates in the hydrolysis of starch.
•• AmyloseAmylose::.. Straight chain compoundStraight chain compound
present in the form glucose unitspresent in the form glucose units
linked bylinked by --1,41,4--glucosidic bond of aglucosidic bond of a
helix formed of a large number ofhelix formed of a large number of --
CH 2 OH
CH 2 OH
It forms the inner part of starch granules
‐ is the storage polysaccharide in animals.
‐ It is a more highly branched structure than amylopectin, with chains
of 12–14 α‐D‐glucopyranose residues in α[1 → 4]‐glucosidic linkage),
with branching by means of α(1 → 6)‐glucosidic bonds
is a polysaccharide of FRUCTOSE (and hence a fructosan)
found in plants.
It is readily soluble in water .
is used to determine the glomerular filtration rate.
‐Is the chief constituent of the framework of plants.
‐It is insoluble
‐consists of β‐D‐glucopyranose units linked by β(1 → 4) bonds to form
long, straight chains strengthened by cross‐linked hydrogen bonds.
Cellulose cannot be digested by mammals because of the absence
of an enzyme that hydrolyzes the β linkage. It is an important
source of “bulk” in the diet. So prevent constipation.
is a structural polysaccharide in the exoskeleton of crustaceans
and insects and also in mushrooms.
It consists of N‐acetyl‐D‐glucosamine units joined by
β (1 →4)‐glycosidic linkages
‐ Glycosaminoglycans are long linear (unbranched)
heteropolysaccharide chains generally composed of a repeating
disaccharide unit (acidic sugar‐amino sugar)n.
‐The amino sugar is either D‐glucosamine or D‐galactosamine in
which the amino group is usually acetylated, and sometimes
There are 6 types:
1. heparin. 2. heparan sulphate. 3. dermatan sulphate
4. keratan s 5. Chondroitin s 6. hyaluronic acid
All of the glycosaminoglycans except hyaluronic acid and heparin are
found covalently attached to protein, forming proteoglycan
Their property of holding large quantities of water and occupying
space lubricating other structures, is due to the large number of OH
groups and negative charges on the molecules, which, by repulsion,
keep the carbohydrate chains apart.
‐Are proteins to which oligosaccharides are covalently attached.
‐ Oligosaccharide chains formed mainly of sialic acids and L‐fucose.
‐ Sialic acids are N‐ or O‐derivatives of neuraminic acid .
‐ Neuraminic acid is a nine‐carbon sugar derived from mannosamine
• Glycoproteins have many functions:
• 1- Soluble as enzymes, hormones and
• 2- In lysosomes
• 3- attached to the cell membrane (The
membrane bound glycoproteins) participate
– a- cell surface recognition (by other cells,
– b- Cell surface antigenicity (as blood gp
- Repeating disaccharide unit
- Linear (unbranched)
- Contain uronic acids (glucuronic
- N- acetyl hexosamine
- Contain hexoses as galactose (in
- contain sulphate
- No pentoses
- No deoxy sugar
- No repeating units
- contain sialic acid derivatives
- N- acetyl hexasamine
- Contain hexoses as galactose
- No sulphate
- Contain pentose
-Contain deoxy sugar as L-fucose
2- Tissue distribution and
- Cell membrane
Functional and structural
- Blood groups antigens
- some hormones
- Immunoglobulins and
- Neuraminic Acid=sialic acid = mannosamine
+ pyruvic acid
= amino sugar acid
- NANA found in glycoproteins.
Found in glycoprotein