Polysaccharide Learning Material

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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 cellwall in plants & algae.

 – Agar  – natural component of certain seaweed polymer of galactose & sulfur containing carbohydrates.

 – Chitin – polymer of glucosamine (an amino sugar), foundin the exoskeleton of bugs.

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Starch

• Starch is used for energy storage in plants

• Two types: amylose and amylopectin. On completehydrolysis each type gives only D-glucose

•  Amylose: is composed of continuous, unbranchedchains of up to 4000 D-glucose units joined bya-1,4-glycoside bonds

•  Amylopectin: is a highly branched polymer of D-glucose. Chains consist of 24-30 units of D-glucose joined by a-1,4-glycoside bonds andbranches created by a-1,6-glycoside bonds

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Amylose• Soluble starch, polymer of D-glucose.

• Starch-iodide complex, deep blue.

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Amylopectin

Branched, insoluble fraction of starch.

A-1,4-glycosidic linkage

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Glycogen

• Glucose polymer, similar to amylopectin, buteven more highly branched.

•Energy storage in muscle tissue and liver.

•The many branched ends provide a quick means of 

putting glucose into the blood.

• A nonlinear polymer of D-glucose units joined

by a-1,4- and a-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.

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Cellulose• Polymer of D-glucose, found in plants.

• Mammals lack the -glycosidase enzyme.Average molecular weight of 400,000,corresponds to

approximately 2800 D-glucose units per molecule.

OCH2OH

HOOH

O

OOCH2OH

HOOH

O

O HO

CH2OH

OH

O

-glucosidic linkage

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Chitin• Polymer of  N -acetylglucosamine.

•Exoskeleton of insects.

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Polysaccharides Digestion

Glucose Polymers

Starch is digestable

Cellulose is not 

digestable by humans

Why?

It’s

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Modification of Cellulose

• Cellulose Nitrate  guncotton 

•

Pyroxylin Partially nitrated photographic film 

•Cellulose Acetate film

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Cellulose fibre - Rayon

Cellulose OH Cellulose O-Na+NaOH

Cellulose OCS-Na+

S

S C S

Sodium salt of a xanthate ester

H+

spinneret Cellulose OH

Cellulose fibre

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Biological Sugars and reactions

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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 eachother; they act as antigenic determinants

•

among the first discovered of these antigenicdeterminants are the blood group substances

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ABO Blood Classification

NAGal Gal NAGluCell membrane

of erythrocyte

-1,4-) -1,3-) -1-)

Fuc

-1,2-)

NAGal = N-acetyl-D-galactosamineGal = D-galactose

NAGlu = N-acetyl-D-glucosamine

Fuc = L-fucose

missing in

type O blood

D-galactose intype B blood

•In the ABO system, individuals are classified

according to four blood types dependent upon whichsugars are present on the surface

•  A, B, AB, and O

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‘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

Gl A

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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 thepresence of acetic acid to give an imine which has ablue-green color 

 – the intensity of the absorption at 625 nm is proportional tothe glucose concentration

• Galactose, mannose, and to a lesser extent lactose andxylose also react with o-toluidine to give colored iminesand, therefore, have the potential for false positive.

samples as small as 20 L (microliters) can be used.

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Glucose Assay• The glucose oxidase method is completely

specific for D-glucose

+

+

glucoseoxidase

D-Gluconic acid

Hydrogen

peroxide

- D-Glucopyranose

OHOH

HO

HOCH2 OH

O

H2 O2

O2

+ H2

O

CO2 H

CH2 OH

OHH

HHO

OHH

OHH

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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 concentrationis determined spectrophotometrically

peroxidase+colored product+o-toluidine H2 O2

H2 O

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Vitamin C - A monosaccharide?• Vitamin C, vital for life is a necessary part of our 

diet because we cannot synthesize it. (Mostplants and animals except primates and guineapigs 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).

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Glycocalyx 

The outer viscous covering of fibersextending from a bacterium

composition: The glycocalyx is usually a viscous

polysaccharide and polypeptide slime. 

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Glycocalyx of 

IntestinalEpithelium

Note that some

carbohydrates are

covalently attached tomembrane

components, while

others are secreted as

extracellular matrix

Fig 16, The Cell, D.W.Fawcett (1981)

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Glycocalyx of Lymphocyte

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Diagram of Glycocalyx

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Ribonucleosides

A -D-ribofuranoside bonded to a heterocyclicbase at the anomeric carbon.

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Ribonucleotides

Add phosphate at 5’ carbon. 

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Nucleic Acids

• Polymer of ribofuranoside ringslinked by phosphate esters.

•Each ribose is bonded to a base. 

•Ribonucleic acid (RNA)

•Deoxyribonucleic acid (DNA)

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Structure of RNA

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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 formthe primary structure.

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Base Pairings

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DNA Replication

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Other Nucleotides

• Adenosine monophosphate (AMP), aregulatory hormone.

• Nicotinamide adenine dinucleotide

(NAD), a coenzyme.

• Adenosine triphosphate (ATP), an energy source.