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CH2210 Carbohydrates II
Disaccharides, Oligosaccharides, and
Polysaccharides
Factors to Consider in the Study of Biomolecules
Do the small building blocks function by themselves ?
Are the building blocks put together into larger structures ?
What are the physical properties of these larger structures ?
How are the various types of biomolecules suited for their individual functions ?
✔
Carbohydrates - Cyclic Structures
In solution, glucose exists in a variety of forms.
Walter Norman Haworth Born March 19, 1883
Nobel Prize in Chemistry, 1937
ascorbic acid
glucose
Carbohydrates - Glycoside Formation
The linkage between the sugar and the alcohol is called a glycosidic linkage and must be designated as α or β. Glycosides of simple monosaccharides are not reducing sugars because the aldehyde functional group is no longer present. The alcohol which attaches through the glycosidic can be another carbohydrate.
Disaccharides - Formed by Condensation
O
OH
OH
HO
HO
CH2OH
O
OH
OH
HO
HO
CH2OH
O
OH
HO
HO
CH2OH
O
OH
OH
HO
CH2OH
O
H2O
C6H12O6 + C6H12O6 ---------> C12H22O11 + H2O
+
Disaccharides What Does the Hydrolysis Reaction Imply?Hydrolysis of a Disaccharide:
Formation of a Glycosidic Bond:
Carbohydrates - Glycoside Formation
an α-1,4 disaccharide a β-1,4 disaccharide
Carbohydrates - Glycoside Formation
Maltose - malt sugar (C12H22O11) From partial hydrolysis of starch
A reducing sugar
Maltose
HYDROLYSIS
D-glucose + D-glucose
Disaccharides - Structure of MaltoseThe structures of the common dietary disaccharides can be
partially deduced from their chemical and physical properties.
Disaccharides - Structure of Maltose
α-D-Glucose α or β-D-Glucose
O
OH
OH
HO
CH2HO
OH
O
OH
OH
HO
CH2HO
H
OH
+
Maltose O
OH
OH
CH2HO
O
OH
OH
HO
CH2HO
O
H
OH
H2O
α-1,4-Glycosidic Bond
1 4
1 4
Lactose - milk sugar (C12H22O11) Found in milk
A reducing sugar
Lactose
HYDROLYSIS
D-galactose + D-glucose
Disaccharides - Structure of Lactose
Disaccharides - Structure of Lactose
O
OH
OHHO
CH2HO
OH O
OH
OH
HO
CH2HO
H
OH
+
β-D-Galactose α or β-D-Glucose
O
OH
OH
CH2HO
O
OH
OHHO
CH2HOO
H
OHLactose
H2O
14
1
4
β-1,4-Glycosidic Bond
Disaccharides Why are Maltose and Lactose Reducing Sugars ?
*
Maltose O
OH
OH
CH2HO
O
OH
OH
HO
CH2HO
O
H
OH
O
OH
OH
CH2HO
O
OH
OHHO
CH2HOO
H
OHLactose
Hemiacetal linkages
which can open to an aldehyde
Disaccharides - Structure of Sucrose
Sucrose - table sugar (C12H22O11) Found in sugar cane and beets
NOT a reducing sugar
Sucrose
HYDROLYSIS
D-glucose + D-fructose
Disaccharides - Structure of Sucrose
NOT a reducing sugar !
α-D-Glucose
O
OH
OH
HO
CH2HO
OH
OHO
OH
CH2HO
CH2HO
+OH
β-D-Fructose
OHO
OH
CH2HO
CH2
OH
OH
H2O
O
OH
OH
HO
CH2HO
O
OHO
OH
CH2HO
CH2 OH
Sucrose
1 2
1 2
1
2
α-1,2-Glycosidic Bond
Structure of Common Disaccharides
Disaccharides - Digestion and Absorption
1) The sugars maltose (from starch digestion), lactose, and sucrose cannot be directly absorbed from the intestinal track.
2) Each must first be enzymatically hydrolyzed to the constituent monosaccharides:
Maltose ------------> glucose + glucose
Lactose -------------> glucose + galactose
Sucrose -------------> glucose + fructose
Enzymes are usually named by adding the suffix –ase to the name of the compound undergoing the reaction.
maltase
lactase
sucrase
Disaccharides - Lactose Intolerance
O
OH
HO
OH OH
OO
HOOH
OH
OH
O
OH
HO
OH OH
OH
HO O
HOOH
OH
OH
Lactase
Lactose
Galactose
Glucose
Oligosaccharides - Cell Recognition1) Cells interact with and
recognize other cells through a process called cell
recognition.
2) Cell recognition is accomplished through
saccharides attached to the cell surfaces.
3) The 0ligosaccharides are present as glycolipids
and glycoproteins.
4) The lipid or protein part of the molecule is integrated
into the cell-membrane structure with the saccharide part located on the external
membrane surface. INSIDE OF CELL
OUTSIDE OF CELL
Oligosaccharide
Membrane protein
Oligosaccharides - Cell Recognition
The ABO blood group types are: A, B, AB, and O.
These result from three types of
antigens (containing saccharide molecules) A, B, and O.
There are only two types of antibodies: anti-A and anti-B. There is no anti-O. O-Antigen
Gal
GlcNAc
Gal
Fuc
β-1,3
β-1,3
α-1,2
A-Antigen
Gal
GlcNAc
Gal
Fuc
β-1,3
β-1,3
α-1,2
GalNAcα-1,3
B-Antigen
Gal
GlcNAc
Gal
Fuc
β-1,3
β-1,3
α-1,2
Galα-1,3
Characteristic A B AB Oantigen on RBC
surface A B A,B NONE
antibodies produced
anti-B anti-A none anti-A, anti-B
can receive RBCs from blood type O, A O, B O,A,B,AB Ocan donate RBCs
to blood type A, AB B, AB AB O,A,B,AB
ABO Blood-Typing System
Blood Types
Polysaccharides
Biological polymers containing large numbers (hundreds or thousands) of monosaccharides residues (repeat units) bonded together.
Starch and glycogen serve as storage forms for D-glucose.
Starch - plants
Glycogen - animals
Cellulose and chitin serve as biological structural materials.
Polysaccharides
Polysaccharides differ in the following ways:
1) The monosaccharides which constitute the residues
2) Which of the hydroxyl groups participate in linking the monosaccharide residues together
3) The type of glycosidic linkage (α or β) involved between the residues
4) The presences or absence of branching
Polysaccharides - Starch Found in Plants
Starch: 10-30% Amylose, 70-90% Amylopectin
Amylose: linear, α(1→4) linkages
Amylopectin:branched, α(1→4) linkages and α(1→6) branches
α -1, 6’ glucosidic linkagebranching point
Polysaccharides
Amylose, amylopectin, and glycogen all contain a single free hemiacetal hydroxyl and hundreds or thousands of acetal glycosidic linkages. The percentage of free hemiacetal –OH groups is so small that none of these molecules give a positive test with Benedict’s solution. They are all non-reducing sugars.
Polysaccharides -Glycogen Found in Animals
Glycogen is similar to amylopectin but more highly branched.
Polysaccharides - 3D Structure of Amylose
Polysaccharides - 3D Structures
Polysaccharides - Starch and Glycogen Digestion
Starch is digested to D-glucose:
Amylase hydrolyzes amylose and parts of amylopectin to maltose in the digestive tract.
Maltase cleaves maltose to D-glucose.
The result of amylase digestion of amylopectin is dextrin which contains the remaining α(1→6) linkages. Dextrin is hydrolyzed by dextrinase to D-glucose.
Polysaccharides - Starch and Glycogen Digestion
Some of the D-glucose from starch is used immediately for energy by cells (glycolysis).
The excess D-glucose is stored in the liver and skeletal muscles as glycogen (glycogenesis). Any D-glucose still in excess is
converted to fat and deposited in the fat tissues. (lipogenesis)
When required for energy or biosynthesis, D-glucose is released from a glycogen molecule (glycogenolysis). Removal of D-
glucose from glycogen can be very rapid because it can be removed from all of the tips of the glycogen branches
simultaneously.
Finally, if the body’s glycogen and glucose stores are depleted, glucose can be supplied by combining smaller molecules in the
liver (gluconeogenesis or glucogenesis).
Polysaccharides - CelluloseCellulose is a β (1→4) Polymer of D-Glucose
Cellulose (wood) is insoluble and retains its shape and most of its
physical strength when placed in water.
Cellulose molecules exist in an
extended chain conformation and pack side to side to form ribbons. The ribbons pack side to side and
on top of each other to form fibers.
All of the cellulose molecules are held together in a fiber by
intermolecular hydrogen bonding.
Comparing Starch and CelluloseUnlike cellulose, starch swells and forms a colloidal suspension when placed in water.
Starch can be differentiated from cellulose by adding a few drops of I2 solution. I2 forms a dark blue solution in the presence of starch which does not form with cellulose.
Humans cannot digest cellulose because we lack the enzyme cellulase which cleaves β(1→4)
linkages. Even so, cellulose in the diet has some beneficial effects.
The main nutritional carbohydrate for grazing animals is cellulose (grass and other plants).
The main nutritional carbohydrate for termites is found in wood.
These animals cannot digest cellulose directly, but have symbiotic microorganisms in their
digestive tracts that secrete cellulase into the animal’s digestive tracts.
Comparing Starch and Cellulose
Supplement: Lactose Intolerance
vs Galactosemia
an accumulation of galactose in the blood
GalactoseGlucoseUridineAdenine
Causes of Galactosemia
-O-P-O-P-O-O❘ ❘❘
O-
O❘ ❘❘
O--1-O-P-O-
O❘ ❘❘
O--6-O-P-O-
O❘ ❘❘
O-
-O-P-O-P-O-P-O-O❘ ❘❘
O-
O❘ ❘❘
O-
O❘ ❘❘
O--O-P-O-P-O-
O❘ ❘❘
O-
O❘ ❘❘
O-
UTPGLYCOLYSIS
-1-O-P-O-O❘ ❘❘
O-
-O-P-O-P-O-P-O-O❘ ❘❘
O-
O❘ ❘❘
O-
O❘ ❘❘
O-
-O-P-O-P-O-O❘ ❘❘
O-
O❘ ❘❘
O-
Galactokinase
ATP
-O-P-O-P-O-O❘ ❘❘
O-
O❘ ❘❘
O-
Galactose-1-phosphateuridyl transferase
UDP-Galactose4’-epimerase
GLYCOCONJUGATES
O
OH
OHHO
CH2HO
OH
O
OH
OH
HOCH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OH
O
OH
OH
HO
CH2O
OH
P
O
O
OO
OH
OH
HO
CH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
O
OH
OHHO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
OO
OP
O
OO
OP
OO
OP
O
OO
P
O O
O
OHOH
CH2O NO
P
OO
N
N
N
NH2
OP
O
OO
P
O O
O
OHOH
CH2O N
N
N
N
NH2
Galactokinase
Galactose-1-phosphateuridyl transferase
UDP-Galactose4’-epimerase
Causes of Galactosemia
O
OH
OHHO
CH2HO
OH
O
OH
OH
HOCH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OH
O
OH
OH
HO
CH2O
OH
P
O
O
OO
OH
OH
HO
CH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
O
OH
OHHO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
OO
OP
O
OO
OP
OO
OP
O
OO
P
O O
O
OHOH
CH2O NO
P
OO
N
N
N
NH2
OP
O
OO
P
O O
O
OHOH
CH2O N
N
N
N
NH2
Galactokinase
Galactose-1-phosphateuridyl transferase
UDP-Galactose4’-epimerase
Causes of Galactosemia
O
OH
OHHO
CH2HO
OH
O
OH
OH
HOCH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OH
O
OH
OH
HO
CH2O
OH
P
O
O
OO
OH
OH
HO
CH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
O
OH
OHHO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
OO
OP
O
OO
OP
OO
OP
O
OO
P
O O
O
OHOH
CH2O NO
P
OO
N
N
N
NH2
OP
O
OO
P
O O
O
OHOH
CH2O N
N
N
N
NH2
Galactokinase
Galactose-1-phosphateuridyl transferase
UDP-Galactose4’-epimerase
Causes of Galactosemia
O
OH
OHHO
CH2HO
OH
O
OH
OH
HOCH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OH
O
OH
OH
HO
CH2O
OH
P
O
O
OO
OH
OH
HO
CH2HO
OP
O
OO
O
OH
OH
HO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
O
OH
OHHO
CH2HO
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
O
OO
P
O O
O
OHOH
CH2O N
NH
O
O
OP
OO
OP
O
OO
OP
OO
OP
O
OO
P
O O
O
OHOH
CH2O NO
P
OO
N
N
N
NH2
OP
O
OO
P
O O
O
OHOH
CH2O N
N
N
N
NH2
Galactokinase
Galactose-1-phosphateuridyl transferase
UDP-Galactose4’-epimerase
Causes of Galactosemia
Consequences of Galactosemia
