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.