Chemistry of carbohydrates used for health science stufents

Chemistry of carbohydrates

1. CHEMISTRY OF CARBOHYDRATES CHEMISTRY OF CARBOHYDRATES
¾ ¾
Carbohydrates are organic substances with C, H Carbohydrates are organic substances with C, H andO intheratioof1:2:1.(C andO intheratioof1:2:1.(C
6 6
H H
12 12
O O
6 6
) )
and

O

in
the
ratio
of
1:2:1.

(C and

O

in
the
ratio
of
1:2:1.

(C
6 6
H H
12 12
O O
6 6
) )
¾ ¾
Defined as Defined as polyhydroxy polyhydroxyaldehyde aldehydeor or ketone ketone di i di i d
er
i
vat
i
ves.
d
er
i
vat
i
ves.
1] 1] Monosaccharides Monosaccharides. .
Simple sugars & cannot be Simple sugars & cannot be hydrolysed hydrolysedfurther. further. Theya
r
e
f
u
r
the
r
class
ifi
edonthebas
i
sof Theya
r
e
f
u
r
the
r
class
ifi
edonthebas
i
sof
They

ae

uthe
class ed

on
the
bass

o They

ae

uthe
class ed

on
the
bass

o
number of carbon atoms present as well as on number of carbon atoms present as well as on th ff ti l th ff ti l
Dr. S Nayak1
th
e presence o
f
f
unc
ti
ona
l
groups.
th
e presence o
f
f
unc
ti
ona
l
groups.

2. Carbon atoms Carbon atoms Exam
p
les Exam
p
les Functional
g
rou
p
s Functional
g
rou
p
s
p p
gp gp
Trioses (3 carbon) Trioses (3 carbon) Glyceraldehyde Glyceraldehyde Aldehyde (aldotriose) Aldehyde (aldotriose)
Dihydroxy acetone Ketone (Ketotriose) Dihydroxy acetone Ketone (Ketotriose)
Tetroses (4 carbon) Tetroses (4 carbon) Erythrose Erythrose Aldehyde (aldotetrose) Aldehyde (aldotetrose)
Pentoses (5 carbon) Pentoses (5 carbon) Ribose Ribose Aldehyde(Aldopentose) Aldehyde(Aldopentose)
Xl Xl
Aldhd(Ald ) Aldhd(Ald )
X
y
l
ose
X
y
l
ose
Ald
e
h
y
d
e
(Ald
opentose
) Ald
e
h
y
d
e
(Ald
opentose
)
Xylulose Xylulose Ketone (Ketopentose) Ketone (Ketopentose)
Hexoses(6carbons) Hexoses(6carbons)
Glucose Glucose
Aldehyde(Aldohexose) Aldehyde(Aldohexose)
Hexoses
(6
carbons) Hexoses
(6
carbons)
Glucose Glucose
Aldehyde
(Aldohexose) Aldehyde (Aldohexose)
Galactose Galactose Aldehyde (Aldohexose) Aldehyde (Aldohexose)
Fructose Fructose Ketone
(
Ketohexose
)
Ketone
(
Ketohexose
)

() ()
2 Dr. S Nayak

3. 2] Disaccharides 2] Disaccharides. .
Contain two molecules of same or different Contain two molecules of same or different
monosaccharide units. monosaccharide units. Onhydrolysis theygivetwomonosaccharideunits. Onhydrolysis theygivetwomonosaccharideunits. On
hydrolysis

they
give

two

monosaccharide
units.

On
hydrolysis

they
give

two

monosaccharide
units.

Monosaccharide units are joined by Monosaccharide units are joined by glycosidic glycosidic bond. bond.
Exam
p
les Exam
p
les Product formed Product formed Gl
y
cosidic Gl
y
cosidic Sources Sources
p p
y y
Upon hydrolysis Linkage Upon hydrolysis Linkage
„ „
Maltose glucose + glucose Maltose glucose + glucose α α1 1--44MaltMalt
„ „
Lactose Lactose
galactose galactose
+glucose +glucose
β β
1 1
4 4
Milk Milk
„ „
Lactose

Lactose

galactose galactose
+

glucose +

glucose
β β
1 1
- -
4 4
Milk Milk
„ „
Sucrose glucose + Fr uctose Sucrose glucose + Fr uctose β β1 1--22 Sugar cane Sugar cane
„ „
Isomaltose Isomaltose glucose + glucose glucose + glucose α α1 1--6 Digestion of 6 Digestion of
li li
amy
l
opect
i
n amy
l
opect
i
n
3] Oligosaccharides 3] Oligosaccharides
Cti3 Cti3
10 l l f h id it 10 l l f h id it
3 Dr. S Nayak
C
on
t
a
i
n
3

C
on
t
a
i
n
3
--
10
mo
l
ecu
l
es o
f
monosacc
h
ar
id
e un
it
s.
10
mo
l
ecu
l
es o
f
monosacc
h
ar
id
e un
it
s.
E.g. E.g. Maltotriose Maltotriose. (Glucose + Glucose + Glucose) . (Glucose + Glucose + Glucose)

4. 44
] Polysaccharides ] Polysaccharides
Contain more than ten molecules of monosaccharide units Contain more than ten molecules of monosaccharide units
T
hey are further classified into
T
hey are further classified into homopolysaccharides homopolysaccharidesand and
heteropolysaccharides heteropolysaccharides
a a
) ) Homopolysaccharide Homopolysaccharide: :
Polymer of same Polymer of same monosacchraide monosacchraideunits units
Examples Monosaccharide Unit Sources
„
Starch
Glucose
Plant rice
„
Starch

Glucose
Plant
,
rice
„
Dextrin Glucose from starch hydrolysis
„
Glycogen Glucose liver, muscle
„
Clll
Gl
Pl ntfib r
„
C
e
ll
u
l
ose
Gl
ucose
Pl
a
nt
fib
e
r
s
„
Inulin Fructose dahlia roots
„
Chitin N-acetyl glucosamine Shells of arthropod
4 Dr. S Nayak

5. Starch: „
I
samixtureoftwopolysaccharides 1)
Amylose
„
I
s

a

mixture
of
two
polysaccharides
,
1)
Amylose
and 2) Amylopectin.
5 Dr. S Nayak

6. Difference between Difference between amylose amylose
and and amylopectin amylopectin
are: are:
Amylose Amylose AmylopectinAmylopectin
1.Amount present 1.Amount present
in starch in starch 1515--20%20% 8080--85%85%
2. Structure 2. Structure Unbranched, linear Unbranched, linear Highly branched. Highly branched. 3.Molecular Weight 3.Molecular Weight
60 60
kDa kDa
500 500
kDa kDa
3.Molecular Weight 3.Molecular Weight
60 60
kDa kDa
500 500
kDa kDa
4.Linkage 4.Linkage 250 to 300 glucose residues 250 to 300 glucose residues glucose residues joined by glucose residues joined by
joined by joined by α α1 1--4 4 by by α α1 1--4 linkages 4 linkages
glycosidic glycosidic link link Branch point occurs by Branch point occurs by
α α
- -11--6 6 glycosidic glycosidic link. link.
5.Reaction with 5.Reaction with Blue color forms because Blue color forms because Reddish violet color Reddish violet color
Iodine solution Iodine solution the iodine molecules are the iodine molecules are
trapped inside the helical trapped inside the helical
structure. Color disappears structure. Color disappears
upon heating. Reappears upon upon heating. Reappears upon
cooling! cooling!
6 Dr. S Nayak

7. Glycogen Glycogen
Stored in liver and muscle. Stored in liver and muscle. Polymer of glucose units. Polymer of glucose units.
Also called as animal starch. Also called as animal starch.
Simil rt th Simil rt th
mlp tin mlp tin
mp n nt f t r h mp n nt f t r h
Simil
a
r
t
o
th
e
Simil
a
r
t
o
th
e a
m
y
l
o
p
ec
tin
a
m
y
l
o
p
ec
tin
co
mp
o
n
e
nt
o
f
s
t
a
r
c
h
. co
mp
o
n
e
nt
o
f
s
t
a
r
c
h
.
It has more branches than starch. There are 11 to 18 It has more branches than starch. There are 11 to 18
g
lucose residues between an
y
branch
p
oints.
g
lucose residues between an
y
branch
p
oints.
gyp gyp
Dextrin Dextrin
T
hese are partially hydrolyzed product of starch
T
hese are partially hydrolyzed product of starch . .
Cellulose Cellulose
Made up of β-D glucose joined by β1-4 glycosidic
bonds
Digested by cellulase enzyme in animals which is
7 Dr. S Nayak
absent in human body.

8. Acts as dietary fiber and adds bulk to the food and helps Acts as dietary fiber and adds bulk to the food and helps
in
p
eristalsis. in
p
eristalsis.
p p
Inulin Inulin Consists of a small number of Consists of a small number of
β β
D D--fructose joined by fructose joined by
ββ2 2--1 1 glycosidic glycosidiclinkages linkages
Iti dt m r th Iti dt m r th
lmrlr lmrlr
filtrtinrt filtrtinrt
It
i
s use
d
t
o
m
easu
r
e
th
e
It
i
s use
d
t
o
m
easu
r
e
th
e g
l
o
m
e
r
u
l
a
r
g
l
o
m
e
r
u
l
a
r
filtr
a
ti
o
n
r
a
t
e,
filtr
a
ti
o
n
r
a
t
e,aa
test to assess the function of kidney. test to assess the function of kidney.
b) b) Heteropolysaccharide Heteropolysaccharide
Theyarepolymerofdifferentmonosaccharide Theyarepolymerofdifferentmonosaccharide They
are
polymer
of

different

monosaccharide They
are
polymer
of

different

monosaccharide
units or their derivatives units or their derivatives
E.
g
. E.
g
. Muco
p
ol
y
saccharides Muco
p
ol
y
saccharides
(
MPS
)
and blood
g
rou
p

(
MPS
)
and blood
g
rou
p

8 Dr. S Nayak
g g
py py
() gp () gp
substances substances

9. Mucopolysaccharides (MPS) are Hyaluronic acid,
Chondroitin sulfate
,
He
p
arin
,
keratan sulfate
,
He
p
aran
Mucopolysaccharidesare heteropolysaccharides
,p, ,p
sulfate and dermatan sulfate Proteoglycan
–
protein = MPS
MPS are also known as glycosaminoglycans
Biomedical importance of MPS Biomedical importance of MPS
They are the components of ground substances They are the components of ground substances th h tth t ll l th h tth t ll l th
roug
h
ou
t

th
e ex
t
race
ll
u
l
ar space.
th
roug
h
ou
t

th
e ex
t
race
ll
u
l
ar space.
They are attached to proteins and form They are attached to proteins and form proteoglycans proteoglycans. .
™ ™
Hyaluronic Hyaluronic
acid acid
actsasa actsasa
barrierintissues barrierintissues
againstthe againstthe
™ ™
Hyaluronic Hyaluronic
acid acid
acts
as
a

acts
as
a
barrier
in

tissues barrier
in

tissues
against
the

against
the

penetration of bacteria. penetration of bacteria.
™ ™
He
p
arin He
p
arinacts as acts as anticoa
g
ulant anticoa
g
ulantin vitro as well as in in vitro as well as in
9 Dr. S Nayak
p p
g g
vivo. It inhibits thrombin. vivo. It inhibits thrombin.

10. ISOMERISM ISOMERISMININCARBOHYDRATES CARBOHYDRATES
• •
The The
presence presence
of of
asymmetric asymmetric
carbon carbon
atoms atoms
(A (A
• •
The The
presence presence
of of
asymmetric asymmetric
carbon carbon
atoms atoms
(A (A
carbon carbon atomatom toto which which fourfour different different atoms atoms oror g
rou
p
s
g
rou
p
s attached attached isis known known asas as
y
mmetric as
y
mmetric
gp gp
y y
carbon) carbon) inin aa compound compound produces produces following following
effect effect;;
• •
It gives rise to the formation of It gives rise to the formation of sterioisomerism sterioisomerism
of that compound of that compound
• •
It also confers optical activity to the compound. It also confers optical activity to the compound.
1. 1. Sterioisomerism Sterioisomerism
C CC
ompounds which are identical in composition
C
ompounds which are identical in composition
and structural formula but differ in spatial and structural formula but differ in spatial
configurationarecalledas configurationarecalledas
sterioisomers sterioisomers
These These
10 Dr. S Nayak
configuration

are

called

as

configuration

are

called

as

sterioisomers sterioisomers
.
These
.
These

include include
• •

11. a. a. Enantiomer Enantiomer::D and L D and L--sugars are referred to as sugars are referred to as enantiomers enantiomers. Their structures . Their structures
are mirror images of each other. are mirror images of each other.
Only D Only D--glucose or D glucose or D--sugars are utilized by humans. sugars are utilized by humans.
DandL DandL
- -
glucosearetermedDandLformdependingonthe glucosearetermedDandLformdependingonthe
D

and

L D

and

L
- -
glucose

are

termed

D

and

L

form

depending

on

the

glucose

are

termed

D

and

L

form

depending

on

the

arrangement of arrangement of H Hand and OH OHon the penultimate carbon atom. on the penultimate carbon atom.
When the sugar has OH group on right, is D isomer. When the sugar has OH group on right, is D isomer.
If OH group is on left side then it is L If OH group is on left side then it is L – –isomer. isomer.
11 Dr. S Nayak

12. B. B. AA
nomerism nomerism
Sugarsinsolutionexistinringformandnotinstraightchain Sugarsinsolutionexistinringformandnotinstraightchain Sugars

in

solution

exist

in

ring

form

and

not

in

straight

chain

Sugars

in

solution

exist

in

ring

form

and

not

in

straight

chain

form. form.
A
ldosu
g
a
r A
ldosu
g
a
r
form mainl
y
form mainl
y

py
ranose
py
ranoserin
g
and rin
g
and ketosu
g
a
r
ketosu
g
a
r
form form
g g
y y
py py
g g
g g
furanose furanosering structure ring structure
Carbon Carbon 1 1, after ring formation becomes asymmetric and it is , after ring formation becomes asymmetric and it is
calledas calledas
anomeric anomeric
carbonatom Ifthetwosugarswhichdiffer carbonatom Ifthetwosugarswhichdiffer
called

as

called

as

anomeric anomeric
carbon

atom
.
If

the

two

sugars

which

differ

carbon

atom
.
If

the

two

sugars

which

differ

in the configuration at only in the configuration at only C1 C1in case of in case of aldoses aldosesand and C2 C2in in
ketoses are known as ketoses are known as anomers anomersand represented as alpha and and represented as alpha and
beta sugars. beta sugars.
E.g. E.g. α α- -D glucose and D glucose and β β- -DD--glucose glucose
Dfructoseand Dfructoseand
β β
D D
fructose fructose
α α- -
D

fructose

and

D

fructose

and

β β
- -
D D
- -
fructose fructose
12 Dr. S Nayak

13. 13 Dr. S Nayak

14. „„
Epimerism Epimerism
::
Theisomersformedduetovariationsinthe Theisomersformedduetovariationsinthe The

isomers

formed

due

to

variations

in

the

The

isomers

formed

due

to

variations

in

the

configuration of configuration of – –HHand and – –OHOHaround a single carbon around a single carbon
atominasugarmoleculeiscalledas atominasugarmoleculeiscalledas
epimers epimers
atom

in

a

sugar

molecule

is

called

as

atom

in

a

sugar

molecule

is

called

as

epimers epimers
. .
Mannose is 2 Mannose is 2 ––epimer epimerof glucose because these of glucose because these
twohavedifferentconfigurationonlyaroundC2 twohavedifferentconfigurationonlyaroundC2 two

have

different

configuration

only

around

C2
.
two

have

different

configuration

only

around

C2
.
Galactose Galactoseis 4is 4--epimer of glucose [at C4] epimer of glucose [at C4]
14 Dr. S Nayak

15. 2.
Optical activity Thecompoundshavingasymmetriccarbonatoms The
compounds

having

asymmetric
carbon
atoms

can rotate the beam of plane polarized light and are
said to be optically active.
An isomer which can rotate the plane of polarized light to the right is called as dextrorotatory and is designatedas
(d)or(+)
designated
as
(d)

or
(+)
Example: D-(d)-glucose or it is also known as dextrose. dextrose.

While the isomer which rotates the plane of
polarized light to left is known as levorotatory, and
is identified as (l) or (-).
Example: D-(l)-fructose.
15 Dr. S Nayak

16. A
compound with D-configuration can be
dextrorotatory (D+) or levorotatory (D-).
E.g. D + glucose and D-fructose.
„„
Glycosidic bond Glycosidic bond
It is the linkage formed between It is the linkage formed between OH OHgroup of group of
anomeric carbon anomeric carbonof one sugar with any of one sugar with any OH OHgroup group
of another sugar (or alcohol) resulting in the loss of of another sugar (or alcohol) resulting in the loss of
awatermolecule Thislinkageisinvolvedinthe awatermolecule Thislinkageisinvolvedinthe a
water
molecule
.
This
linkage
is
involved

in

the

a
water
molecule
.
This
linkage
is
involved

in

the

formation of disaccharide and polysaccharides. formation of disaccharide and polysaccharides.
16 Dr. S Nayak

17. „„
Reduction tests Reduction tests Dh ff Dh ff
ldhd ldhd
D
ue to t
h
e presence o
f
a
f
ree
D
ue to t
h
e presence o
f
a
f
ree a
ld
e
h
y
d
e a
ld
e
h
y
d
eor or
ketone ketonegroup, carbohydrates are readily group, carbohydrates are readily
idi d idi d
dbh h d i dbh h d i
ox
idi
se
d
ox
idi
se
d
an
d

b
e
h
ave as t
h
e re
d
uc
i
ng agents. an
d

b
e
h
ave as t
h
e re
d
uc
i
ng agents.
These sugars have the capacity to reduce These sugars have the capacity to reduce
ii (C ii (C
2+ 2+
)i(C )i(C
+ +
) )
cupr
i
c
i
on
(C
u cupr
i
c
i
on
(C
u
2+ 2+
)
to cuprous
i
on
(C
u
)
to cuprous
i
on
(C
u
+ +
)
.
)
.
Therefore the Therefore the reducing sugar reducing sugarlike like glucose glucosewill will
i i
ii B di i ii B di i
g
i
ve g
i
ve pos
i
t
i
ve
B
ene
di
cts react
i
ons pos
i
t
i
ve
B
ene
di
cts react
i
ons. .
NonNon--reducing sugars reducing sugars like likesucrose sucrosewill respond will respond
to these tests provided it is first to these tests provided it is first hydrolysed hydrolysedinto into
its reducing components glucose and fructose. its reducing components glucose and fructose.
17 Dr. S Nayak

18. Functions of carbohydrates Functions of carbohydrates
1 1
Mostabundantdietarysourceofenergy(4Cal/g) Mostabundantdietarysourceofenergy(4Cal/g)
1
.
1
.
Most
abundant
dietary
source
of

energy
(4Cal/g)

Most
abundant
dietary
source
of

energy
(4Cal/g)

2. 2.
They are precursors for many organic compounds (fats, They are precursors for many organic compounds (fats, aminoacids) aminoacids) amino
acids) amino acids)
3. 3.
Carbohydrates (glycoprotein, glycolipids) participate in Carbohydrates (glycoprotein, glycolipids) participate in thestructureofcellmembraneandcellularfunctions thestructureofcellmembraneandcellularfunctions the
structure
of

cell
membrane
and

cellular
functions the
structure
of

cell
membrane
and

cellular
functions
4. 4.
Structural components of many organisms. These Structural components of many organisms. These
in
c
l
ude
th
e
fi
be
r
s
(ce
ll
u
l
ose)
o
f
p
lant
,
e
x
os
k
e
l
e
t
o
n
o
f in
c
l
ude
th
e
fi
be
r
s
(ce
ll
u
l
ose)
o
f
p
lant
,
e
x
os
k
e
l
e
t
o
n
o
f
cude e bes(ce uose)o p ,e os eeo o cude e bes(ce uose)o p ,e os eeo o
some insects and the cell wall of microorganisms. some insects and the cell wall of microorganisms.
5. 5.
Serve as the stora
g
e form of ener
gy

(g
l
y
co
g
en
)
to meet Serve as the stora
g
e form of ener
gy

(g
l
y
co
g
en
)
to meet
ggy(gyg) ggy(gyg)
the immediate energy demands of the body. the immediate energy demands of the body.
18 Dr. S Nayak
Reference: Essentials of Biochemistry by Dr S Nayak Reference: Essentials of Biochemistry by Dr S Nayak