Carbohydrates
(Several descriptive slides are
added as notes,They are not
slides for real lecture)
Carbohydrates are
polyhydroxy
aldehydes and
ketones which
have chemical
formulae which
resemble hydrated
carbons,hence the
name
carbohydrate,All
of the common
sugars found in
living systems
contain either a
free or potentially
free aldehyde or
ketone,
The term carbohydrate derives from the
fact that many of them have a formula that
can be simplified to (CH2O)n,Some of
these compounds are chemically modified,
however,and do not fit the formula due to
the modification.
Saccharides
Saccharide is another name for a carbohydrate,
Simple saccharides are the monosaccharides,
commonly called sugars,Glucose is an example
of a monosaccharide,We use terms
monosaccharide,oligosaccharide,or
polysaccharide to refer to compounds composed
of a single sugar,several sugars linked together,
or many sugars linked together,respectively.
Saccharides play a variety of roles in living
organisms,including energy storage,structural
roles (RNA and DNA,cell wall,exoskeleton),and
cell identity.
Monosaccharide
Monosaccharide is another term for a simple
sugar,such as glucose,which is not linked to any
other sugars.
Common monosaccharides include:
Glucose Mannose
Fructose Ribose
Galactose Erythrose
Monosaccharide nomenclature
? are the simplest sugars,having the formula
(CH2O)n,The smallest molecules usually
considered to be monosaccharides are those
with n = 3
? Category
? 3-------------Triose
? 4-------------Tetrose
? 5------------- Pentose
? 6--------------Hexose
? 7--------------Heptose
? 8--------------Octose
?Monosaccharides containing an aldehyde group are
called aldoses.
?Monosaccharides containing a ketone group are
called ketoses.
?Monosaccharides that form five member rings are
called furanoses.
?Monosaccharides that form six member rings are
called pyranoses.
Carbons in a monosaccharide are
numbered such that the aldehyde group is
carbon number one or the ketone group is
carbon number two
Sucrose is composed of a
pyranose and a furanose
The simplest member
of the carbohydrate
family is
glyceraldehyde,Since
glyceraldehyde
contains an
asymmetric or chiral
carbon,it can be found
in two stereoisomeric
forms designated as D-
or L-,Almost every
sugar found in animals
is related to D -
glyceraldehyde,
although there are a
few rare exceptions
such as L- Fucose,
found in glycoproteins,
etc,
The enantiomers of
glyceraldehyde
Fischer projection
A Fischer projection is a
convention for representing
stereoisomers in a plane,The
tetrahedron of bonds on a carbon is
represented as a plane cross,where
the bonds to the right and left are
assumed to be pointing toward the
viewer and the bonds to the top and
bottom are assumed to be pointing
away from the viewer,Projections of
monosaccharides are oriented with
the carbonyl group at the top; the
chiral carbon farthest from the
carbonyl group (which is the one that
determines whether the sugar is the
D or the L form) is then drawn with
its hydroxyl to the right for the D
form and to the left for the L form.
Stereoisomers,diastereomers,
enantiomers
For a chiral or asymmetric carbon,
there are 2 forms,In general a molecule
with m chiral centers will have 2(m)
stereoisomers,The multiple stereoisomeric
forms means that not all stereoisomers
will be mirror images of each other.
Stereoisomers that are not mirror images
of each other are called diastereomers
D-glyceraldehyde and L-glyceraldehyde
are mirror images of each other,called
enantiomers,and stereoisomers at the
same time,and cannot be superimposed
on each other
Stereoisomers =
Diastereomers + enantiomers
Ketose-aldose pairs of sugars frequently
are named by inserting the letters 'ul' in
the name of the corresponding aldose to
derive the name of the ketose,An
example is erythrose - erythrulose.
This figure shows the
structure of alpha,D-
glucose in what is know
as the Haworth
Projection format,In
solution,glucose is an
equilibrium mixture
between the free
aldehyde or open chain
form and the cyclized
form shown here in
which an internal hemi-
acetal is formed between
carbons 1 and 5.
Haworth projection
A Haworth projection is
a conventional planar
representation of a
cyclized mono saccharide
molecule,The hydroxyls
that are represented to
the right of the chain in a
Fischer projection are
shown below the plane in
a Haworth projection,
Plane of the ring is
perpendicular to that of
the paper and the heavy
line projects towards the
reader
Anomers
When sugars cyclize,they typically form furanose or
pyranose structures,These are molecules with five-
membered or six-membered rings,respectively,
Cyclization creates a carbon with two possible
orientations of the hydroxyl around it,We refer to this
carbon as the anomeric carbon and the two possible
forms as anomers,The two possible configurations of
the hydroxyl group are called alpha and beta,which
correspond to the hydroxyl being in the "down" and
"up" positions,respectively,in standard projections
Epimers
Two sugars that differ only by the
configuration around one carbon,
While there are
dozens of
carbohydrate
structures found
in living systems,
some are more
commonly found,
Shown here as
Haworth
projections are
glucose and
galactose,Note
that galactose is
an epimer (optical
isomer) of glucose
at carbon 4.
While there are
dozens of
carbohydrate
structures found
in living systems,
some are more
commonly found,
Shown here as
Haworth
projections are
glucose and
mannose,Note
that mannose is
an epimer
(optical isomer)
of glucose at
carbon 2.
While there are
dozens of
carbohydrate
structures found in
living systems,some
are more commonly
found,Shown here
as Haworth
projections are
glucose and fucose,
Note the telltale
methyl group rather
than an hydroxyl at
carbon 6 and the
optical configuration
at carbon 5,
indicating an L-sugar,
not epimers.
The pyranose ring in chair and
boat conformations
Terminology describing sugar
structure
? Stereoisomers
? Diastereomers
? Enantiomers
? Epimers
? Anomers
? Alpha and beta configuration
Oligosaccharides
? Formation of glycosidic bonds
between monosaccharides give rise to
oligosaccharides and polysaccharides.
? The simplest oligosaccharides,the
disaccharides,include compounds such
as sucrose,maltose and lactose
Glycosidic bonds
? Glycosides are formed by elimination of
water between the anomeric hydroxyl of a
cyclic monosaccharide and the hydroxyl
group of another compound,Glycosides
do not undergo mutarotation,so they
remain locked in the alpha or beta
configuration,
The formation of a
glycosidic bond involves
the interaction of an
hydroxyl group from
another molecule
(normally another sugar
molecule) with the
reducing carbon to form
an acetal with the
resulting loss of water,
This is a stable bond and
requires hydrolysis in
order to split the two
sugars apart again,
? Formation of glycosidic bonds need energy
imput
? Hydrolysis of glycosidic bonds are
thermodynamically favorable
Nomenclature 1
The naming rules for oligosaccharides
based on these abbreviations are as
follows:
1,The sequence starts with the nonreducing
end at the left using the abbreviations.
2,Anomeric and enantiomeric forms are
designated by prefixes (e.g.,alpha,D-)
Reducing sugar
? Sugars that can reduce Fe(3+) or Cu(2+)
ion are called reducing sugars,The
carbonyl group is oxidized to carboxyl
group,
? Monosaccharides are reducing sugars.
? In disaccharides or polysaccharides the
end of a chain with a free anomeric
carbon is called the reducing end.
An example of a common
glycosidic bond is shown here
between fructose and glucose
to form the common
disaccharide,sucrose,This is
an unusual disaccharide in that
the reducing groups of the two
sugars are both involved in the
bond between the two sugars,
Note that carbon 1 of the
glucose is linked to carbon 2 of
the fructose,
An example of a common
glycosidic bond is shown here
between galactose and glucose
to form the common disaccharide,
lactose or "milk sugar" as it is
sometimes known due to its high
concentration in milk,Note that
carbon 1 of the galactose is
linked to carbon 4 of the glucose,
Milk intolerance
? Genetic deficiency
? While almost all infants can digest lactose,
many adults are lactase-deficient to some
extent,3% Danes and 97% of Thais are
deficient in lactase,Lactose accumulation
in small intestine leads to fluid loss and
diarrhea,
? Milk can be treated with lactase for lactose
intolerant people
Mobilizable glucose,glycogen,
starch and dextran
Glycogen
Most glycosidic bonds in glycogen are
alpha-1,4-glycosidic bonds,branches are
alpha-1,6-glycosidic bonds,about once in
ten units in glycogen,In glycogen,
branches increase the release from the
many non-reducing ends.
Starch
? Starch contains two types of glucose
polymer,amylose and amylopectin
? Amylose consists of long,unbranched
chains of D-glucose,
? Amylopectin is highly branched,alpha-1,6-
glycosidic bond once in about 30 units,
? No reducing end in the branches
Cellulose and chitin,linear chains of
glucose for structural purpose
In cellulose and chitin,sugar units are
joined by beta linkages,The straight
chains formed by beta linkages is optimal
for structural function
Mammals lack cellulase to digest cellulose
in wood and vegetable fibers,Ruminants
(such as sheep or cow) harbor cellulase-
producing bacteria in their digestive tract
and they can digest cellulose.
Exoskeletons of insect and crab (crustacea)
contains chitin,Chitin is polymer of N-
acetylglucosamine in beta-1,4 linkage,
Chitin is like cellulose except at C-2
position –OH is replaced by an acetylated
amino group,
Glycosaminoglycans
The most abundant heteropolysaccharides in the
body are the glycosaminoglycans (GAGs),These
molecules are long unbranched polysaccharides
containing a repeating disaccharide unit,The
disaccharide units contain either of two modified
sugars--- N-acetylgalactosamine (GalNAc) or N-
acetylglucosamine (GlcNAc) and a uronic acid
such as glucuronate or iduronate,
GAGs are highly negatively charged
molecules,with extended conformation that
imparts high viscosity to the solution,GAGs
are located primarily on the surface of cells or
in the extracellular matrix (ECM),Along with
the high viscosity of GAGs comes low
compressibility,which makes these
molecules ideal for a lubricating fluid in the
joints,At the same time,their rigidity
provides structural integrity to cells and
provides passageways between cells,
allowing for cell migration.
Examples of some common
Glycosaminoglycans
Proteoglycans
? The majority of GAGs in the body are
linked to core proteins,forming
proteoglycans (also called
mucopolysaccharides),Proteoglycans
are macromolecules containing
glycosaminoglycan,whose structure
components are simple and repetitive.
? Highly negatively charged.
? On cell surface or Extracellular matrix.
The GAGs of proteglycan extend
perpendicularly from the core in a
brush-like structure,The linkage of
GAGs to the protein core involves a
specific trisaccharide composed of
two galactose residues and a
xylulose residue (GAG-GalGalXyl-O-
CH2-protein),The attachment is
through S or T,or O-linked.
Glycoproteins and glycolipid
? Glycoproteins,Proteins with one or more
oligosaccharides joined covalently,More than
half of all eukaryotic proteins carry covalently
attached oligosaccharide or polysaccharide
chains,Glycoproteins differ from proteoglycans
by 1) carbohydrate components 2) glycoprotein
bonds 3) sizes of saccharides attached.
? Glycolipid,Membrane lipid with oligosaccharides
attached to the hydrophilic side.
Glycoprotein bonds
Lectins are carbohydrate-
binding proteins
? Canavalin A (jack bean),binds to internal and
nonreducing terminal alpha-mannose
? Wheat germ agglutinin,peanut lectin and
phytohemagglutinin (red kidney bean) recognize
disaccharide or oligosaccharide units,
? All lectins contains multiple carbohydrate binding
sites,explaining their ability to agglutinate
(crosslink) erythrocytes and other cells
Roles of lectins
? Binding of nitrogen fixing bacterium
(Rhizobium trifolli) to the surface of root
hairs,
? Adherence of E.coli to epithelial cells of
gastrointestinal tract,
? Influenza virus contains hemagglutinin
that recognizes sialic acid on cells lining
the respiratory tract
Selectins,homing receptors
that bind carbohydrates
? Lymphocytes tend to migrate to where
they were originated,called homing,This
is mediated by interaction of receptors on
lymphocytes and carbohydrates on the
endothelial lining of lymph nodes,
? Selectins also mediate the binding of
neutrophils and other leukocytes to sites
of injury in the inflammatory response,
Peptidoglycan in bacterial cell
wall
Peptidoglycans
? Bacterial walls contain a heteropolymer of
alternating beta-1,4-linked
acetylglucosamine and N-acetylmuramic
acid,The polymers lie side by side,cross-
linked by short peptides.
? Lysozyme kills bacteria by hydrolizing the
glycosidic bond,Penicillin kills by
preventing the synthesis of cross-links,
(Several descriptive slides are
added as notes,They are not
slides for real lecture)
Carbohydrates are
polyhydroxy
aldehydes and
ketones which
have chemical
formulae which
resemble hydrated
carbons,hence the
name
carbohydrate,All
of the common
sugars found in
living systems
contain either a
free or potentially
free aldehyde or
ketone,
The term carbohydrate derives from the
fact that many of them have a formula that
can be simplified to (CH2O)n,Some of
these compounds are chemically modified,
however,and do not fit the formula due to
the modification.
Saccharides
Saccharide is another name for a carbohydrate,
Simple saccharides are the monosaccharides,
commonly called sugars,Glucose is an example
of a monosaccharide,We use terms
monosaccharide,oligosaccharide,or
polysaccharide to refer to compounds composed
of a single sugar,several sugars linked together,
or many sugars linked together,respectively.
Saccharides play a variety of roles in living
organisms,including energy storage,structural
roles (RNA and DNA,cell wall,exoskeleton),and
cell identity.
Monosaccharide
Monosaccharide is another term for a simple
sugar,such as glucose,which is not linked to any
other sugars.
Common monosaccharides include:
Glucose Mannose
Fructose Ribose
Galactose Erythrose
Monosaccharide nomenclature
? are the simplest sugars,having the formula
(CH2O)n,The smallest molecules usually
considered to be monosaccharides are those
with n = 3
? Category
? 3-------------Triose
? 4-------------Tetrose
? 5------------- Pentose
? 6--------------Hexose
? 7--------------Heptose
? 8--------------Octose
?Monosaccharides containing an aldehyde group are
called aldoses.
?Monosaccharides containing a ketone group are
called ketoses.
?Monosaccharides that form five member rings are
called furanoses.
?Monosaccharides that form six member rings are
called pyranoses.
Carbons in a monosaccharide are
numbered such that the aldehyde group is
carbon number one or the ketone group is
carbon number two
Sucrose is composed of a
pyranose and a furanose
The simplest member
of the carbohydrate
family is
glyceraldehyde,Since
glyceraldehyde
contains an
asymmetric or chiral
carbon,it can be found
in two stereoisomeric
forms designated as D-
or L-,Almost every
sugar found in animals
is related to D -
glyceraldehyde,
although there are a
few rare exceptions
such as L- Fucose,
found in glycoproteins,
etc,
The enantiomers of
glyceraldehyde
Fischer projection
A Fischer projection is a
convention for representing
stereoisomers in a plane,The
tetrahedron of bonds on a carbon is
represented as a plane cross,where
the bonds to the right and left are
assumed to be pointing toward the
viewer and the bonds to the top and
bottom are assumed to be pointing
away from the viewer,Projections of
monosaccharides are oriented with
the carbonyl group at the top; the
chiral carbon farthest from the
carbonyl group (which is the one that
determines whether the sugar is the
D or the L form) is then drawn with
its hydroxyl to the right for the D
form and to the left for the L form.
Stereoisomers,diastereomers,
enantiomers
For a chiral or asymmetric carbon,
there are 2 forms,In general a molecule
with m chiral centers will have 2(m)
stereoisomers,The multiple stereoisomeric
forms means that not all stereoisomers
will be mirror images of each other.
Stereoisomers that are not mirror images
of each other are called diastereomers
D-glyceraldehyde and L-glyceraldehyde
are mirror images of each other,called
enantiomers,and stereoisomers at the
same time,and cannot be superimposed
on each other
Stereoisomers =
Diastereomers + enantiomers
Ketose-aldose pairs of sugars frequently
are named by inserting the letters 'ul' in
the name of the corresponding aldose to
derive the name of the ketose,An
example is erythrose - erythrulose.
This figure shows the
structure of alpha,D-
glucose in what is know
as the Haworth
Projection format,In
solution,glucose is an
equilibrium mixture
between the free
aldehyde or open chain
form and the cyclized
form shown here in
which an internal hemi-
acetal is formed between
carbons 1 and 5.
Haworth projection
A Haworth projection is
a conventional planar
representation of a
cyclized mono saccharide
molecule,The hydroxyls
that are represented to
the right of the chain in a
Fischer projection are
shown below the plane in
a Haworth projection,
Plane of the ring is
perpendicular to that of
the paper and the heavy
line projects towards the
reader
Anomers
When sugars cyclize,they typically form furanose or
pyranose structures,These are molecules with five-
membered or six-membered rings,respectively,
Cyclization creates a carbon with two possible
orientations of the hydroxyl around it,We refer to this
carbon as the anomeric carbon and the two possible
forms as anomers,The two possible configurations of
the hydroxyl group are called alpha and beta,which
correspond to the hydroxyl being in the "down" and
"up" positions,respectively,in standard projections
Epimers
Two sugars that differ only by the
configuration around one carbon,
While there are
dozens of
carbohydrate
structures found
in living systems,
some are more
commonly found,
Shown here as
Haworth
projections are
glucose and
galactose,Note
that galactose is
an epimer (optical
isomer) of glucose
at carbon 4.
While there are
dozens of
carbohydrate
structures found
in living systems,
some are more
commonly found,
Shown here as
Haworth
projections are
glucose and
mannose,Note
that mannose is
an epimer
(optical isomer)
of glucose at
carbon 2.
While there are
dozens of
carbohydrate
structures found in
living systems,some
are more commonly
found,Shown here
as Haworth
projections are
glucose and fucose,
Note the telltale
methyl group rather
than an hydroxyl at
carbon 6 and the
optical configuration
at carbon 5,
indicating an L-sugar,
not epimers.
The pyranose ring in chair and
boat conformations
Terminology describing sugar
structure
? Stereoisomers
? Diastereomers
? Enantiomers
? Epimers
? Anomers
? Alpha and beta configuration
Oligosaccharides
? Formation of glycosidic bonds
between monosaccharides give rise to
oligosaccharides and polysaccharides.
? The simplest oligosaccharides,the
disaccharides,include compounds such
as sucrose,maltose and lactose
Glycosidic bonds
? Glycosides are formed by elimination of
water between the anomeric hydroxyl of a
cyclic monosaccharide and the hydroxyl
group of another compound,Glycosides
do not undergo mutarotation,so they
remain locked in the alpha or beta
configuration,
The formation of a
glycosidic bond involves
the interaction of an
hydroxyl group from
another molecule
(normally another sugar
molecule) with the
reducing carbon to form
an acetal with the
resulting loss of water,
This is a stable bond and
requires hydrolysis in
order to split the two
sugars apart again,
? Formation of glycosidic bonds need energy
imput
? Hydrolysis of glycosidic bonds are
thermodynamically favorable
Nomenclature 1
The naming rules for oligosaccharides
based on these abbreviations are as
follows:
1,The sequence starts with the nonreducing
end at the left using the abbreviations.
2,Anomeric and enantiomeric forms are
designated by prefixes (e.g.,alpha,D-)
Reducing sugar
? Sugars that can reduce Fe(3+) or Cu(2+)
ion are called reducing sugars,The
carbonyl group is oxidized to carboxyl
group,
? Monosaccharides are reducing sugars.
? In disaccharides or polysaccharides the
end of a chain with a free anomeric
carbon is called the reducing end.
An example of a common
glycosidic bond is shown here
between fructose and glucose
to form the common
disaccharide,sucrose,This is
an unusual disaccharide in that
the reducing groups of the two
sugars are both involved in the
bond between the two sugars,
Note that carbon 1 of the
glucose is linked to carbon 2 of
the fructose,
An example of a common
glycosidic bond is shown here
between galactose and glucose
to form the common disaccharide,
lactose or "milk sugar" as it is
sometimes known due to its high
concentration in milk,Note that
carbon 1 of the galactose is
linked to carbon 4 of the glucose,
Milk intolerance
? Genetic deficiency
? While almost all infants can digest lactose,
many adults are lactase-deficient to some
extent,3% Danes and 97% of Thais are
deficient in lactase,Lactose accumulation
in small intestine leads to fluid loss and
diarrhea,
? Milk can be treated with lactase for lactose
intolerant people
Mobilizable glucose,glycogen,
starch and dextran
Glycogen
Most glycosidic bonds in glycogen are
alpha-1,4-glycosidic bonds,branches are
alpha-1,6-glycosidic bonds,about once in
ten units in glycogen,In glycogen,
branches increase the release from the
many non-reducing ends.
Starch
? Starch contains two types of glucose
polymer,amylose and amylopectin
? Amylose consists of long,unbranched
chains of D-glucose,
? Amylopectin is highly branched,alpha-1,6-
glycosidic bond once in about 30 units,
? No reducing end in the branches
Cellulose and chitin,linear chains of
glucose for structural purpose
In cellulose and chitin,sugar units are
joined by beta linkages,The straight
chains formed by beta linkages is optimal
for structural function
Mammals lack cellulase to digest cellulose
in wood and vegetable fibers,Ruminants
(such as sheep or cow) harbor cellulase-
producing bacteria in their digestive tract
and they can digest cellulose.
Exoskeletons of insect and crab (crustacea)
contains chitin,Chitin is polymer of N-
acetylglucosamine in beta-1,4 linkage,
Chitin is like cellulose except at C-2
position –OH is replaced by an acetylated
amino group,
Glycosaminoglycans
The most abundant heteropolysaccharides in the
body are the glycosaminoglycans (GAGs),These
molecules are long unbranched polysaccharides
containing a repeating disaccharide unit,The
disaccharide units contain either of two modified
sugars--- N-acetylgalactosamine (GalNAc) or N-
acetylglucosamine (GlcNAc) and a uronic acid
such as glucuronate or iduronate,
GAGs are highly negatively charged
molecules,with extended conformation that
imparts high viscosity to the solution,GAGs
are located primarily on the surface of cells or
in the extracellular matrix (ECM),Along with
the high viscosity of GAGs comes low
compressibility,which makes these
molecules ideal for a lubricating fluid in the
joints,At the same time,their rigidity
provides structural integrity to cells and
provides passageways between cells,
allowing for cell migration.
Examples of some common
Glycosaminoglycans
Proteoglycans
? The majority of GAGs in the body are
linked to core proteins,forming
proteoglycans (also called
mucopolysaccharides),Proteoglycans
are macromolecules containing
glycosaminoglycan,whose structure
components are simple and repetitive.
? Highly negatively charged.
? On cell surface or Extracellular matrix.
The GAGs of proteglycan extend
perpendicularly from the core in a
brush-like structure,The linkage of
GAGs to the protein core involves a
specific trisaccharide composed of
two galactose residues and a
xylulose residue (GAG-GalGalXyl-O-
CH2-protein),The attachment is
through S or T,or O-linked.
Glycoproteins and glycolipid
? Glycoproteins,Proteins with one or more
oligosaccharides joined covalently,More than
half of all eukaryotic proteins carry covalently
attached oligosaccharide or polysaccharide
chains,Glycoproteins differ from proteoglycans
by 1) carbohydrate components 2) glycoprotein
bonds 3) sizes of saccharides attached.
? Glycolipid,Membrane lipid with oligosaccharides
attached to the hydrophilic side.
Glycoprotein bonds
Lectins are carbohydrate-
binding proteins
? Canavalin A (jack bean),binds to internal and
nonreducing terminal alpha-mannose
? Wheat germ agglutinin,peanut lectin and
phytohemagglutinin (red kidney bean) recognize
disaccharide or oligosaccharide units,
? All lectins contains multiple carbohydrate binding
sites,explaining their ability to agglutinate
(crosslink) erythrocytes and other cells
Roles of lectins
? Binding of nitrogen fixing bacterium
(Rhizobium trifolli) to the surface of root
hairs,
? Adherence of E.coli to epithelial cells of
gastrointestinal tract,
? Influenza virus contains hemagglutinin
that recognizes sialic acid on cells lining
the respiratory tract
Selectins,homing receptors
that bind carbohydrates
? Lymphocytes tend to migrate to where
they were originated,called homing,This
is mediated by interaction of receptors on
lymphocytes and carbohydrates on the
endothelial lining of lymph nodes,
? Selectins also mediate the binding of
neutrophils and other leukocytes to sites
of injury in the inflammatory response,
Peptidoglycan in bacterial cell
wall
Peptidoglycans
? Bacterial walls contain a heteropolymer of
alternating beta-1,4-linked
acetylglucosamine and N-acetylmuramic
acid,The polymers lie side by side,cross-
linked by short peptides.
? Lysozyme kills bacteria by hydrolizing the
glycosidic bond,Penicillin kills by
preventing the synthesis of cross-links,
