Common Modifications to
Monosaccharides
Deoxy sugars
Amino sugars
Glycosides (acetal)
Deoxy Sugar
Amino Sugar
Glucosamine
HO O
H
H
HO
H
HNH2
H OH
OH
Formation of Glycosides -
Acetals
Glycoside: a carbohydrate in which the -OH of the
anomeric carbon is replaced by -OR
O
OH
O
OCH3
CH3OH
H+
A „glycoside‟ bond
A monosaccharide hemiacetal can react with a
second molecule of an alcohol to form an acetal
Glycosides
• Glycoside bond: the bond from the anomeric
carbon of the glycoside to an -OR group.
• Unlike cyclic hemiacetals, cyclic acetals are
not in equilibrium with their open chain
carbonyl-containing forms.
• Glycosides do NOT undergo mutarotation.
Naming Glycosides
• List the name of the alkyl or aryl group
attached to oxygen followed by the name of
the carbohydrate with the ending -e
replaced by -ide
– methyl -D-glucopyranoside
– methyl -D-ribofuranoside
Glucopyranoside
Methyl -D-glucopyranoside
(methyl -D-glucoside)
O
CH2 OH
H
OH
OCH3 ( )H
HOH
OHH
H
OCH2 OH
HOHO
OHOCH3 ( )
Haworth projection
Chair conformation
Disaccharides
Maltose
Lactose
Sucrose
Maltose
• From malt, the juice of sprouted barley and
other cereal grains
OHO
HO
OH
CH2OH
CH2OH
OH
HO
O
OH
O
-maltose becausethis -OH is beta
-1,4-glycoside bond
-Maltose
Lactose The principle sugar present in milk
about 5% - 8% in human milk, 4% - 5% in cow‟s milk
D-glucopyranose
OCH2OH
HO
OH OH
OH
HO
O
CH2OHO
OH
D-galactopyranose
-1,4-glycosidebond
-lactose becausethis OH is beta
-Lactose
Sucrose • Table sugar, obtained from the juice of
sugar cane and sugar beet
OCH2OH
HO
HO
OHO
CH2OH
OH
OH
CH2OH
O
-D-glucopyranose
-D-fructofuranose
-1,2-glycosidebond
-2,1-glycosidebond
Sucrose
N-Glycosides
• The anomeric carbon of a cyclic hemiacetal
undergoes reaction with the N-H group of an
amine to form an N-glycoside
• N-glycosides of the following purine and pyrimidine
bases are structural units of nucleic acids
HN
N
O
O
H
N
N
NH 2
O
H
HN
N
O
O
H
CH3
Uracil Thymine Cytosine
N-Glycosides
N
N N
N
NH2
HAdenine
anomericcarbon
a -N-glycosidebond
HH
HOHOCH2
HO OH
NH2
O
N
N
H
HN
N N
N
O
HH2N
Guanine
Formation of N-Glycosides
(Nucleosides)
• For example, reaction between -D-ribofuranose
and cytosine produces water and uridine, one of
the structural units of RNA:
OOH
OHOH
HOCH2
N
N
NH2
H
O
+
O
OHOH
HOCH2O
NH2
N
N
-N-glycoside bond
- H2O
-D-Ribofuranose Cytosine
Uridine
anomericcarbon
Disaccharides
• Three naturally occurring glycosidic linkages:
• 1-4‟ link: The anomeric carbon is bonded to oxygen on C4 of second sugar.
• 1-6‟ link: The anomeric carbon is bonded to oxygen on C6 of second sugar.
• 1-1‟ link: The anomeric carbons of the two sugars are bonded through an oxygen.
Cellobiose
• Two glucose units linked 1-4‟.
• Disaccharide of cellulose.
• A mutarotating, reducing sugar.
=>
Maltose
Two glucose units linked 1-4‟.
=>
Lactose
• Galactose + glucose linked 1-4‟.
• “Milk sugar.”
=>
Gentiobiose
• Two glucose units linked 1-6‟.
• Rare for disaccharides, but commonly seen
as branch point in carbohydrates.
=>
Sucrose • Glucose + fructose, linked 1-1‟
• Nonreducing sugar
=>
Polysaccharides • Polysaccharides are chains of five or more monosaccharide:
–Starch – glucose polymer that is the plant storage carbohydrate
–Glycogen – glucose polymer that is the animal storage carbohydrate
–Cellulose – glucose polymer that is a major component of the cell wall in plants & algae.
–Agar – natural component of certain seaweed polymer of galactose & sulfur containing carbohydrates.
–Chitin – polymer of glucosamine (an amino sugar), found in the exoskeleton of bugs.
Starch
• Starch is used for energy storage in plants
• Two types: amylose and amylopectin. On complete hydrolysis each type gives only D-glucose
• Amylose: is composed of continuous, unbranched chains of up to 4000 D-glucose units joined by a-1,4-glycoside bonds
• Amylopectin: is a highly branched polymer of D- glucose. Chains consist of 24-30 units of D- glucose joined by -1,4-glycoside bonds and branches created by -1,6-glycoside bonds
Amylopectin
OCH2OH
HO
OH
O
O
OCH2
HO
OH
O
O
O
OH
HO
CH2OHO
OCH2OH
HO
OH
O
O
OH
HO
CH2OHO
Glycogen
• The reserve carbohydrate for animals
• A nonlinear polymer of D-glucose units joined
by -1,4- and -1,6-glycoside bonds bonds.
• The total amount of glycogen in the body of a
well-nourished adult is about 350 g (about 3/4
of a pound) divided almost equally between
liver and muscle.
Cellulose
• Cellulose is a linear polymer of D-glucose
units joined by -1,4-glycoside bonds.
• Average molecular weight of 400,000,
corresponds to approximately 2800
D-glucose units per molecule.
Cellulose
OCH2OH
HO
OH
O
OOCH2OH
HO
OH
O
O HO
CH2OH
OH
O
Polysaccharides Digestion
Polymers of Glucose
Starch is digestable
Cellulose is not
digestable by humans
Modification of Cellulose
• Cellulose Nitrate guncotton
•Pyroxylin Partially nitrated photographic film
•Cellulose Acetate film
Cellulose fibre - Rayon
Cellulose OH Cellulose O-Na+NaOH
Cellulose OCS-Na+
SS C S
Sodium salt of a xanthate ester
H+
spinneretCellulose OH
Cellulose fibre
Biological Sugars and reactions
Membrane Carbohydrates • Membranes of animal plasma cells have large
numbers of bound small carbohydrates to them.
•these membrane-bound carbohydrates are part of
the mechanism by which cell types recognize each
other; they act as antigenic determinants
•among the first discovered of these antigenic
determinants are the blood group substances
ABO Blood Classification
• at the cellular level, the biochemical basis for
this classification is a group of relatively small
membrane-bound carbohydrates
ABO Blood Classification
NAGal Gal NAGluCell membrane
of erythrocyte
-1,4-) -1,3-) -1-)
Fuc
-1,2-)
NAGal = N-acetyl-D-galactosamine
Gal = D-galactose
NAGlu = N-acetyl-D-glucosamine
Fuc = L-fucose
missing in
type O blood
D-galactose in
type B blood
•In the ABO system, individuals are classified
according to four blood types: A, B, AB, and O
„Chemstrip Kit‟
Blood glucose test for diabetics
Based on reaction of o-toluidine with glucose
CHO
OHH
HO H
OHH
OHH
CH2OH
H2N
H3C
CH
OHH
HO H
OHH
OHH
CH2OH
N
H3C
Glucose Assay
• The o-toluidine test is applied directly to serum, plasma, cerebrospinal fluid, and urine
•Diabetes: A common analytical procedure in the
clinical chemistry laboratory is the determination
of glucose in blood, urine, or other biological fluid
• glucose reacts with 2-methylaniline (o-toluidine) in the presence of acetic acid to give an imine which has a blue-green color
–the intensity of the absorption at 625 nm is proportional to the glucose concentration
• Galactose, mannose, and to a lesser extent lactose and xylose also react with o-toluidine to give colored imines and, therefore, have the potential for false positive.
samples as small as 20 L (microliters) can be used.
Glucose Assay • The glucose oxidase method is completely
specific for D-glucose
+
+
glucose
oxidase
D-Gluconic acid
Hydrogen
peroxide
- D-Glucopyranose
OHOH
HOHO
CH2 OHO
H2 O2
O2 + H2 O
CO2 H
CH2 OH
OHH
HHO
OHH
OHH
Glucose Assay
• O2 is reduced to hydrogen peroxide H2O2
• the concentration of H2O2 is proportional to the
concentration of glucose in the sample
• in one procedure, hydrogen peroxide is used to oxidize
o-toluidine to a colored product, whose concentration
is determined spectrophotometrically
peroxidase+colored product +o-toluidine H2 O2 H2 O
Vitamin C - A monosaccharide? • Vitamin C, vital for life is a necessary part of our
diet because we cannot synthesize it. (Most plants and animals except primates and guinea pigs can make their own Vitamin C).
•It is needed to maintain health of dentine, cartilage,
connective tissue and bone.
•Recommended daily allowance ~45mg for adults
(60mg if pregnant, 80mg if lactating).
Ascorbic Acid (Vitamin C)
• L-Ascorbic acid (vitamin C) is synthesized both
biochemically and industrially from D-glucose
L-ascorbic acidVitamin C
OOHH
CH2OH
O
OHHO
-D-Glucopyranose
O
OH
OH
HO
HO
CH2OH
Biosynthesis from Glucose
Glycocalyx
The outer viscous covering of fibers
extending from a bacterium
composition: The glycocalyx is usually a viscous
polysaccharide and polypeptide slime.
Glycocalyx of
Intestinal
Epithelium
Note that some
carbohydrates are
covalently attached to
membrane
components, while
others are secreted as
extracellular matrix
Fig 16, The Cell, D.W.
Fawcett (1981)
Glycocalyx of Lymphocyte
Diagram of Glycocalyx
Cellulose
• Polymer of D-glucose, found in plants.
• Mammals lack the -glycosidase enzyme.
=>
Amylose • Soluble starch, polymer of D-glucose.
• Starch-iodide complex, deep blue.
=>
Amylopectin
Branched, insoluble fraction of starch.
Glycogen
• Glucose polymer, similar to amylopectin, but even more highly branched.
•Energy storage in muscle tissue and liver.
•The many branched ends provide a quick
means of putting glucose into the blood.
Chitin • Polymer of N-acetylglucosamine.
=>
•Exoskeleton of insects.
Ribonucleosides
A -D-ribofuranoside bonded to a heterocyclic
base at the anomeric carbon.
=>
Ribonucleotides
Add phosphate at 5‟ carbon.
Nucleic Acids
• Polymer of ribofuranoside rings
linked by phosphate esters.
=>
•Each ribose is bonded to a base.
•Ribonucleic acid (RNA)
•Deoxyribonucleic acid (DNA)
Structure of RNA
=>
Structure of DNA
• -D-2-deoxyribofuranose is the sugar.
•Heterocyclic bases are cytosine, thymine
(instead of uracil), adenine, and guanine.
Linked by phosphate ester groups to form
the primary structure.
Base Pairings
=>
Double Helix of DNA
• Two complementary
polynucleotide chains
are coiled into a helix.
•Described by Watson
and Crick, 1953.
DNA Replication
=>
Additional Nucleotides
• Adenosine monophosphate (AMP), a
regulatory hormone.
• Nicotinamide adenine dinucleotide
(NAD), a coenzyme.
• Adenosine triphosphate (ATP), an energy source.