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CARBOHYDRATE METABOLISM
Structure
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Di and oligosaccharides
Polysaccharides
Homo and heteropolysaccharides
Glycoconjugates
Outline
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Disaccharides: Sucrose
Sucrose is formed by linking D-glucose withb
D-fructose to give a 1,2glycosidic link.
CH2
O H
OH H
OH
O H
CH2
OH
OHO
CH2OH
HH
OH
H
OH
OH
H
H1 2
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Disaccharides: Lactose
Lactose is formed by joiningb
D-
galactose to D-glucose to give a 1,4glycoside
O
CH2OH
H
H
OH
H
OH
OH
H H OH
O
CH2OH
HH
H
OH
OH
H
H
O1
b
D-galactose
4
D-glucose
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Disaccharides: Maltose
Maltose is formed by linking two -D-
glucose molecules to give a 1,4glycosidic link.
OH
O
CH2OH
HH
H
OH
OH
H
H
O
O
CH2OH
HH
OH
H
OH
OH
H
H
4-O-a-D-glucopyranosyl-a-D-glucopyranose
14
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Oligosaccharide
An oligosaccharide is a saccharide polymer
containing a small number (typically three toten of component sugars, also known assimple sugars. The name derived from the
Greek ol igos , meaning "a few".
Fructo-oligosaccharides (FOS), which are
found in many vegetables, consist of shortchains of fructose molecules. Inulin has amuch higher degree of polymerization thanFOS and is a polysaccharide
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Oligosaccharide
Fructooligosaccharides (FOS) alsosometimes called oligofructose oroligofructan, is a class of
oligosaccharides used as an artificialor alternative sweetener
Two different classes of FOS mixturesare produced commercially, based oninulin degradation or processes
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Oligosaccharide-Inulin
Inulins are a group of naturally occurringpolysaccharides (several simplesugars linked together) produced bymany types of plants. They are belong
to a class of fibers known as fructans.Inulin is used by some plants as ameans of storing energy and is
typically found in roots or rhizomes.Most plants which synthesize and storeinulin do not store other materials such
as starch
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Polysaccharides: Cellulose
Cellulose is the major structural
polymer in plants. It is a linerhomopolymer composed of bD-glucose units linked
b
-1,4. The
repeating disaccharide of celluloseis b-cellobiose.
Animals lack the enzymes
necessary to hydrolyze cellulose.The bacteria in ruminants (eg.cows) can digest cellulose so that
they can eat grass, etc.
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Polysaccharides: Starch
Starches are storage forms of glucose
found in plants.They are polymers of linked glucose.If the links are only 1,4, the polymer is
linear and is called amylose.Amylose usually assumes a helical
configuration with six glucose units
per turn.If the links are both 1,4 and 1,6, thepolymer is branched and is calledamylopectin.
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Polysaccharides: amylose/amylopectin
O
O
CH2
OH
HH
H
OH
OH
H
H
O
O
CH2
OH
HH
O
H
OH
OH
H
HO
CH2
OH
HH
H
OH
OH
H
H
O
O
CH2
OH
HH
O
H
OH
OH
H
H
amylose
O
O
CH2
OH
HH
H
OH
OH
H
H
O
O
CH2
HH
O
H
OH
OH
H
HO
CH2
OH
HH
H
OH
OH
H
H
O
O
CH2
OH
HH
O
H
OH
OH
H
H
O
O
CH2
OH
HH
H
OH
OH
H
H
O
O
CH2
OH
HH
O
H
OH
OH
H
H Amylopectin
1,6 link at branch
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Polysaccharides: glycogen
The storage carbohydrate in animalsis glycogen. It is a branched chain
polymer like amylopectin but it hasmore frequent branching (aboutevery 10 residues). Glycogen isstored in liver and muscle cells.
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Polysaccharides
Bacterial cell walls haveheteropolysaccharides as majorcomponents.
The polymers consist of chains ofalternating N-acetyl-
b
-D-glucosamine
and N-acetylmuramic acid (next slide).The parallel chains are linked by shortpeptide residues.
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Polysaccharides
O
CH2OH
HH
OH
H
O
NH
HH
OH
C CH3O
CHCH3COO
-
N-acetyl muramic acid
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Glycoconjugates
Glycoconjugates are compounds that
covalently link carbohydrates toproteins and lipids.
Proteoglycans and glycoproteins are
two kinds of glycoconjugates thatcontain protein.
Proteoglycans:
Proteoglycans have a very highcarbohydrate to protein ratio, often
95:5, and are found in the extracellularmatrix.
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Glycoproteins
These materials contain carbohydrateresidues on protein chains.
Important examples of glycoprotein areantibodies-chemicals which bind toantigens and immobilize them.
The carbohydrate part of theglycoprotein plays a role indetermining the part of the antigen
molecule to which the antibody binds.
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Glycoproteins:
The human blood groups A, B, AB,and O depend on theoligosaccharide part of the
glycoprotein on the surface oferythrocyte cells.
The terminal monosaccharide of theglycoprotein at the nonreducingenddetermines blood group.
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Glycoproteins:
Type Terminal sugarA N-acetylgalactosamine
B a-D-galactoseAB both the above
O neither of the above
O is the universal donor
AB is the universal acceptor
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Sugars which are capable to reduce theoxidizing agents such as Tollen
reagents(AgO), Fehling reagents(CuO)called the Reducing Sugars.
Examples: glucose, fructose, maltose,lactose etc
Reducing and Nonreducing Sugar
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Reducing sugar
A reducing sugar is any sugar that, in basic
solution, forms some aldehyde or ketone.
This allows the sugar to act as a reducing
agent, for example in the Maillard reactionand Benedict's reaction.
Those sugar which are unable to reducethe such above oxidizing agents iscalled the Non-reducing sugars.
Examples: Sucrose, Trehalose
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Maillard Reaction:
The Maillard reaction is a chemical reactionbetween an amino acid and a reducing
sugar. Like caramelization (is the oxidationof sugar), it is a form of non-enzymaticbrowning
-This reaction is the basis of the flavoringindustry, since the type of amino aciddetermines the resulting flavor.
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The End
Carbohydrates II
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