Polysaccharides Overview

Polysaccharides

• Polysaccharides are high molecular weight carbohydrates.
• They are insoluble and non-sugars.
• Hydrolysis yields monosaccharides or products related to monosaccharides.
• They are polymeric anhydrides of simple sugars.
• D-glucose is a common component.
• Other constituents include D- and L-galactose, D-mannose, D-xylose, L-arabinose, D-glucuronic, D-galacturonic, D-mannuronic acids, D-glucoseamine, D-galactoseamine, and aminouronic acids.
• Polysaccharides vary in molecular weight, chain nature (linear or branched), and type of glycosidic bond (α or β).
• Chemically, polysaccharides are classified into homo and heteropolysaccharides.
• Homopolysaccharides yield a single monosaccharide on hydrolysis.
• Heteropolysaccharides yield a mixture of monosaccharides on hydrolysis.

Functions of Polysaccharides

• Functions include food and energy storage (e.g., starch, glycogen, inulin) and structural components (e.g., cellulose, pectin, chitin).
• The major purposes of polysaccharides are energy, storage, and structural purposes.
• Polysaccharides provide 50-80% of the body's energy.
• Energy not immediately needed is stored as glycogen.
• Polysaccharides help the body oxidize fats without carbs.
• They spare proteins from being used for energy, enabling them for building/repair of tissues.
• Aids digestion, creates cell/tissue structure, and acts as a carbon source for synthesizing other components.

Storage Polysaccharides

• Starch is a polymer of α-glucose.

• It is stored as starch grains in chloroplasts, storage organs, and seeds.

• Starch is a white, tasteless, odorless powder.

• It's insoluble in cold water or alcohol.

• Starch consists of two molecules: amylose (linear and helical) and amylopectin (branched).

• Amylose is connected by α(1-4) glycosidic bonds.

• Amylopectin contains both α(1-4) and α(1-6) linkages.

• Starch is hydrolyzed to sugars (glucose).

• Starch is commonly found in starchy foods such as bread, cereals, rice, potatoes, beans, and chestnuts.

• Glycogen is a storage form of carbohydrate in animals.

• It is stored in the liver and muscles.

• It may attain up to 7% of animal's wet weight.

• Glycogen is stored in animal cells.

• Glycogen particles are smaller than starch grains.

• Glycogen is formed by D-glucoses linked by α-1,4 and α-1,6 glycosidic bonds.

• Branching occurs after 8-10 residues.

• Inulin is a storage form of carbohydrate found in the tubers of dahlia and artichoke and roots of dandelion.

• It's a polymer of D-fructose linked by β(1,2) linkages.

• It's linear and lacks branching.

• It has a lower molecular weight than starch.

• It colors yellow with iodine.

• Hydrolysis yields fructose.

• Inulin sources include onions, garlic, and Jerusalem artichoke.

Structural Polysaccharides

• Cellulose is the most abundant extracellular structural polysaccharide.

• It's present in all land plants but absent in meat, egg, fish, and milk.

• Cellulose is not digestible by humans.

• It is synthesized and degraded on earth at 1015 kg each year.

• Cellulose comprises about 50% of all carbon in vegetation.

• Cellulose is the most widely distributed carbohydrate in plants.

• It's structurally resistant, fibrous, tough, white, solid, insoluble in water but soluble in ammoniacal cupric hydroxide solution (Schweitzer's reagent), and gives no color with iodine, lacking sweetness.

• Pectin is found as intercellular substances in young plants and ripe fruits like guava, apples, and pears.

• It's a component of the middle lamella between cell walls and adjacent cells.

• It is a polysaccharide of α-D-galacturonic acid, where some free carboxyl groups are esterified with methyl alcohol or combined with calcium or magnesium ions.

• It's called polygalacturonides and has high molecular weights.

• Chitin is an abundant biopolymer found in fungi and arthropods (e.g., crabs, insects).

• Chitin is found in the exoskeleton of insects and crabs and the framework of lobster/crab shells.

• Chitin is hardened with calcium carbonate.

Mucopolysaccharides

• Mucopolysaccharides are polymers of disaccharides (aminosugar-acidsugar).
• One monosaccharide is N-acetyl-glucosamine or -galactosamine.
• The other is D-glucuronic or L-iduronic acid.
• Mucopolysaccharides are gelatinous substances with high molecular weights (up to 5 x 106).
• They are structural support materials for connective tissues and mucous substances, serving as lubricants and cementing substances.
• Hyaluronic acid, chondroitin sulfates (A & C), dermatan sulfate, and heparin are examples.

Hyaluronic Acid

• Hyaluronic acid is a component of various tissues, including the vitreous body of the eye, umbilical cord, and synovial fluid.
• It is the most abundant member of mucopolysaccharides.
• In animals, hyaluronic acid is a high-viscosity biological lubricant largely due to 0.03% hyaluronic acid content.
• Frequently, it's prepared from umbilical cord.
• Chemically, it is a straight-chain polymer of D-glucuronic acid and N-acetyl-D-glucosamine (NAG).
• Hyaluronic acid is an acidic substance with a molecular weight approaching 5,000,000.
• It is connected by β-1,3 and β-1,4 linkages.
• Hyaluronidase is a spreading factor of skin and connective tissue.
• It helps foreign bodies (pigments, pathogens) penetrate the tissue due to depolymerization.
• The enzyme plays a role in fertilization, allowing sperm advancement in the cervical canal.

Chondroitin

• Chondroitin is a component of cartilage and cell coats.
• It is a parent substance of chondroitin sulfate A and chondroitin sulfate B.
• Chemically, chondroitin resembles hyaluronic acid but with galactosamine instead of glucosamine.
• Polysaccharide is a polymer of β-D-glucuronido-1,3-N-acetyl-D-galactosamine joined by β-1,4 linkages.

Chondroitin Sulfates (A & C)

• Chondroitin sulfates A and C are widely distributed and structural components of cartilage, tendons, and bones.
• They are often associated with collagen and other proteins.
• Chondroitin sulfates are derivatives of chondroitin.
• Sulfate groups attached to galactosamine moieties at carbon 4 (chondroitin sulfate A) or 6 (chondroitin sulfate C).
• Linkages are β-1,3 and β-1,4.

Dermatan Sulfate

• Dermatan sulfate is structurally similar to chondroitin sulfate A, but replaces D-glucuronic acid with L-iduronic acid (different at C5).
• It is also known as chondroitin sulfate B.
• It differs from both chondroitin sulfate A and C in its repeating disaccharide unit.
• The linkages are α-1,3 and β-1,4.

Heparin

• Heparin is a sulfated mucopolysaccharide.
• It's found in liver, lung, and arterial walls (wherever mast cells are).
• It likely neutralizes biogenic amines (like histamine).
• Heparin acts as an anticoagulant by inhibiting blood coagulation through the prothrombin-thrombin conversion, eliminating thrombin's effect on fibrinogen.
• Heparin contains more than two carbohydrates in its repeating units.

Proteoglycans

• Proteoglycans are conjugated proteins.
• "Core" proteins are covalently linked to glycosaminoglycans (GAGs).
• These give proteoglycans a large size and high viscosity.

Other Polysaccharides

• Xylans, agar-agar, and vegetable gums are other significant polysaccharides.
• There are different types of important polysaccharides and uses.

Applications

• Polysaccharides are used in various applications, including water treatment, pulp and paper, biomedical (e.g., wound dressings, anticoagulants, tissue engineering, and orthopedic applications).
• Other applications include cosmetics, biotechnology, and agriculture (e.g., seed/leaf coating, hydroponics/fertilizers, and controlled agrochemical release).

This quiz covers the structure, classification, and functions of polysaccharides. Learn about their hydrolysis, components, and roles in food storage and structure. Test your knowledge on homopolysaccharides and heteropolysaccharides.