Carbohydrates Note M.N Chatterjea For Nurses Part V

Afza.Malik GDA

Carbohydrates Note For Nurses Part V

Carbohydrates Note M.N Chatterjea For Nurses Part V

Polysaccharides, Homo-polysaccharides (Homoglycans) ,Biomedical Importance of Hetro-polyssachrides, Proteoglycans Chemistry And Functions,Functions of Proteoglycans.


• Polysaccharides are more complex substances. Some are polymers of a single monosaccharide and are termed as Homopolysaccharides (Homoglycans), e.g. starch, glycogen, etc.

• Some contain other groups other than carbohydrates such as hexuronic acid and are called as Heteropolysaccharides (heteroglycans), e.g. Mucopolysaccharides.

Homo-polysaccharides (Homoglycans)

1. Starch Starch is a polymer of glucose, and occurs in many plants as storage foods. It may be found in the leaves, and stem, as well as in roots, fruits and seeds where it is usually present in greater concentration.

• Starch granules: Appear under microscope as particles made up of concentric layers of material. They differ in shape, size and markings according to the source .Starchy foods are mainstay of our diet.

• Composition of starch granule: It consists of two polymeric units of glucose called (i) Amylose and (ii) Amylopectin, but they differ in molecular architecture and in certain properties.

• Solubility: Starch granules are insoluble in cold water, but when their suspension is heated, water is taken up and swelling occurs, viscosity increases and starch gels or pastes are formed.

• Reaction with I2: Both the granules and the colloidal solutions react with Iodine to give a blue color. This is chiefly due to amylose, which forms a deep-blue complex, which dissociates on heating. Amylopectin solutions are colored blue-violet or purple.

• Ester Formation: Starches are capable of forming esters with either organic or inorganic acids.

• Hydrolysis of starch: It yields succession of polysaccharides of gradually diminishing molecular size

2. Glycogen

Glycogen is the reserve carbohydrate of the animal, hence it is called as animal starch. It has been shown to be present in plants which have no chlorophyll systems, e.g. in fungi and yeasts. It is also found in large amounts in oysters and other shell fish. In higher animals, it is deposited in the liver and muscle as storage material which are readily available as immediate source of energy. It is dextrorotatory with an [α] D 20° is very rapid but ceases when the pH falls to 5.5 due to lactic acid formed from glucose= +196° to +197°.


Glycogens have a complex structure of highly branched chains. It is a polymer of D-Glucose units and resemble amylopectin. Glucose units in main stem are joined by α1 → 4 glucosidic linkages and branching occurs at branch points by α1 → 6 glucosidic linkage. A branch point occurs for every 12 to 18 glucose units Formation of glycogen from glucose is called as Glycogenesis and breakdown of glycogen to form glucose is called as glycogenolysis. Postmortem glycogenolysis

3. Inulin It is a polymer of D-fructose and has a low molecular weight (MW = 5000). It occurs in tubers of the Dehlia, in the roots of the Jerusalem artichoke, dandelion and in the bulbs of onion and garlic. It is a white, tasteless powder. It is levorotatory and gives no colour with iodine. Acids hydrolyse it to D-fructose; similarly it is also hydrolysed by the enzyme inulinase, which accompanies it in plants. It has no dietary importance in human beings as inulinase is absent in human.

Biomedical Importance

• It is used in physiological investigation for determination of the rate of glomerular filtration rate (GFR). • It has been also used for estimation of body water (ECF) volume.

4. Cellulose Cellulose is a polymer of glucose. It is not hydrolyzed readily by dilute acids, but heating with fairly high concentrations of acids yields, the disaccharide Cellobiose and D-Glucose. Cellobiose is made up of two molecules of D-Glucose linked together by β-Glucosidic linkage between C1 and C4 of adjacent glucose units.

Biomedical Importance

Cellulose is a very stable insoluble compound. Since, it is the main constituent of the supporting tissues of plants, it forms a considerable part of our vegetable food. Herbivorous animals, with the help of bacteria, can utilise a considerable proportion of the cellulose ingested, but in human beings no cellulose splitting enzyme is secreted by GI mucosa, hence it is not of any nutritional value. But it is of considerable human dietetic value that it adds bulk to the intestinal contents (roughage) thereby stimulating peristalsis and elimination of indigestible food residues.

5. Dextrins

When starch is partially hydrolysed by the action of acids or enzymes, it is broken down into a number of products of lower molecular weight known as dextrins (see hydrolysis of starch). They resemble starch by being precipitable by alcohol, forming sticky, gummy masses.

Biomedical Importance

• Dextrin solutions are often used as mucilages (mucilages on the back of the postage stamp)

• Starch hydrolysates consisting largely of dextrins and maltose are widely used in infant feeding.

6. Dextrans It is a polymer of D-Glucose. It is synthesised by the action of Leuconostoc mesenteroides, a non-pathogenic gram +ve cocci in a sucrose medium. Exocellular enzyme produced by the organisms bring about polymerisation of glucose moiety of sucrose molecule, and forms the polysaccharide known as Dextrans. They differ from dextrins in structure. They are made up of units of a number of D-Glucose molecules, having α1 → 6, α1 → 4 or α1 → 3 glycosidic linkages, within each unit and the units are joined together to form a network.

Clinical Aspect

Dextran solution, having molecular wt approx. 75,000 have been used as Plasma Expander. When given IV, in cases of blood loss (haemorrhage), it increases the blood volume. Because of their high viscosity, low osmotic pressure, slow disintegration and utilisation, and slow elimination from the body they remain in blood for many hours to exert its effect.


Only disadvantage is that it can interfere with grouping and cross-matching, as it forms false agglutination (Roleux formfation). Hence blood sample for grouping and cross-matching should be collected before administration of dextran in a case of haemorrhage and blood loss, where blood transfusion may be required.

7. Agar It is a homopolysaccharide. Made up of repeated units of galactose which is sulphated. Present in seaweed. It is obtained from them.

Biomedical Importance

• In human: Used as laxative in constipation. Like cellulose, it is not digested, hence add bulk to the faeces (“roughage” value) and helps in its propulsion.

• In microbiology: Agar is available in purified form. It dissolves in hot water and on cooling it sets like gel. It is used in agar plate for culture of bacteria.

Hetero-polysaccharides (Heteroglycans)

Mucopolysaccharides (MPS)

Jeanloz has suggested the name Glycosaminoglycans (GAG) to describe this group of substances. They are usually composed of amino sugar and uronic acid units as the principal components, though some are chiefly made up of amino sugar and monosaccharide units without the presence of uronic acid.

Important ACcidic Hetro polysacheride

Hyaluronic Acid A sulphate free mucopolysaccharide. It was first isolated from vitreous humour of eye. Later it was found to be present in synovial fluid, skin, umbilical cord, haemolytic streptococci and in rheumatic nodule. It occurs both free and salt-like combination with proteins and forms so[1]called ground substance of mesenchyme, an integral part of gel-like ground substance of connective and other tissues.

Biomedical Importance

• The invasive power of some pathogenic organisms may be increased because they secrete hyaluronidase. In the testicular secretions, it may dissolve the viscid substances surrounding the ova to permit penetration of spermatozoa.

• Clinically the enzyme is used to increase the efficiency of absorption of solutions administered by clysis.

Sulphate containing heteropolysaccharides

Sulphate Containing Acid MPS 1. Keratan Sulphate (Kerato Sulphate) A sulphate containing acid MPS. Found in costal cartilage, and cornea has been isolated from bovine cornea. It has been reported to be present in Nucleus pulposus and the wall of aorta.

2. Chondroitin Sulphates They are principal MPS in the ground substance of mammalian tissues and cartilage. They occur in combination with proteins and are called as Chondroproteins.

3. Heparin It is also called α-Heparin. It is an anticoagulant present in liver and it is produced mainly by mast cells of liver (Originally isolated from liver). In addition, it is also found in lungs, thymus, spleen, walls of large arteries, skin and in small quantities in blood.

Proteoglycans Chemistry And Functions

• Proteoglycans are conjugated proteins. Proteins called “core” proteins are covalently linked to glycosaminoglycans (GAGs).

Any of the GAGs viz. hyaluronic acid (HA); keratan sulphates I and II, chondroitin sulphates A, B, C, heparin and heparan sulphate can take part in its formation.

• The amount of carbohydrates in proteoglycans is much greater (upto 95%) as compared to glycoproteins.

Functions of Proteoglycans

• As a constituent of extracellular matrix or ground substance: Interacts with collagen and elastin

• Acts as polyanions: GAGS present in proteoglycans are polyanions and hence bind to polycations and cations such as Na and K. Thus attracts water by osmotic pressure into extracellular matrix contributing to its turgor.

• Acts as a barrier in tissue: Hyaluronic acid in tissues acts as a cementing substance and contributes to tissue barrier which permit metabolites to pass through but resist penetration by bacteria and other infective agents.

• Acts as lubricant in joints: Hyaluronic acid in joints acts as a lubricant and shock absorbant. Intraarticular injection of hyaluronic acid in knee joints is used to alleviate pain in chronic osteoarthritis of knee joints.

• Role in release of hormone: Proteoglycans like hyaluronic acid are present in storage or secretory granules, where they play part in release of the contents of the granules.

• Role in cell migration in embryonic tissues: Hyaluronic acid is present in high concentration in embryonic tissues and is considered to play an important role in cell migration during morphogenesis and wound repair.

• Role in glomerular filtration: Proteoglycans like hyaluronic acid is present in basement membrane (BM) of glomerulus of kidney where it plays important role in chargeselectiveness of glomerular filtration.

• Role as anticoagulant in vitro and in vivo: In vitro, heparin is used as an anticoagulant. 2 mg/10 ml of blood is used. Most satisfactory anticoagulant as it does not produce a change in red cell volume or interfere with its subsequent determinations.  In vivo, heparin is an important anticoagulant. It binds with factor IX and XI, but its most important action is with plasma antithrombin III. Binding of heparin to lysine residues in antithrombin III produces conformational change which promotes the binding of the latter to serine protease thrombin which is inhibited, thus fibrinogen is not converted to fibrin

Four naturally occurring thrombin inhibitors in plasma are:

(i) Antithrombin III (75% of the activity)

(ii) α2-macroglobulin contributes remainder

(iii) Heparin cofactor II

(iv) α1-antitrypsin The last two shows minor activity.

• Role as a coenzyme: Heparin acts in the body to increase the activity of the enzyme Lipoprotein lipase.

Heparin binds specifically to the enzyme present in capillary walls, causing a release of the enzyme into the circulation. Hence heparin is called as Clearing factor. • As a receptor of cell: Proteoglycans like heparan sulphate are components of plasma membrane of cells, where they may act as receptors and can participate in cell adhesion and cell-cell interactions.

• Role in compressibility of cartilages: Chondroitin sulphates and hyaluronic acid are present in high concentration in cartilages and have a role in compressibility of cartilage in weight bearing.

• Role in sclera of eye: Dermatan sulphate is present in sclera of the eye where it has an important function in maintaining overall shape of the eye.

• Role in corneal transparency: Keratan sulphate I is present in cornea of the eye and lie between the collagen fibrils. It plays an important role in maintaining corneal transparency.

Biomedical Importance/Clinical Aspect Mucopolysaccharidoses: 

The mucopolysaccharidoses are a group of related disorders, due to inherited enzyme defect,in which skeletal changes, mental retardation, visceral involvement and corneal clouding are manifested to varying degrees.

Defect/defects in these disorders result in:

• Widespread deposits in tissues of a particular MPS

• In excessive excretion of MPS in urine.


Notes Made By The Help of "The Text Book of Medical Biochemistry By MN. Chatterjea 8th Edition"

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