Carbohydrates Quiz: Starch and Cellulose

Homogenous Polysaccharides

• Starch is formed from two chief constituents: amylose and amylopectin

• Amylose is a straight chain and helical structure formed from α-D-glucose units linked by α-1-4 glycosidic linkages

• It gives a blue color with iodine and forms the inner part of the granule, constituting 15-20% of starch granule

• Amylopectin is a highly branched chain formed from α-D-glucose units linked by α-1-4 glycosidic linkage and α-1-6 glycosidic linkage at point of branching

• It gives a violet color with iodine and forms the outer part of the granule, constituting 80-85% of starch granule

• Partial hydrolysis with amylase enzyme or acids gives various types of dextrins

• Complete hydrolysis by amylase enzyme gives amylose

• Complete hydrolysis by acid gives glucose units

• Dextrin is produced by hydrolysis of starch (amylopectin) and includes amylodextrin, erythrodextrin, and achrodextrin

• Dextran is produced by bacteria, formed from α-D-glucose linked by α-1-3, 1-4, and 1-6 glycosidic linkage

• It is used in hypovolemia as fluid therapy for shock treatment and in emergency as supportive treatment

• Glycogen is called animal starch and is the main storage form of carbohydrates in animal tissues (liver and muscle)

Heterogenous Polysaccharides

• Hyaluronic acid is formed from β-glucuronic acid attached to β-N-acetyl glucosamine by β-1-3 and 1-4 glycosidic linkages

• It is present in subcutaneous tissues, synovial fluid, vitreous humor of the eye, and umbilical cord

• It hydrolyzed by hyaluronidase enzyme present in heads of sperms and secreted by some bacteria

• Chondroitin sulfates are formed from β-glucuronic acid attached to β-N-acetyl galactosamine by β 1-3 and β 1-4 glycosidic linkages

Other Polysaccharides

• Inulin is formed from repeated units of α-D fructose joined by α 1-2 glycosidic linkage

• It is soluble in warm water and is used in investigation of glomerular filtration (GFR) as it is not absorbed by renal tubules

• Chitin is found in the exoskeleton of insects (invertebrates) and is formed from β-N-acetyl glucosamine units linked by β-1-4 glycosidic linkage

• It is insoluble in water, acid, and alkalis

• Cellulose is the most abundant carbohydrate found in nature and is formed from β-D-glucose linked by β-1,4 glycosidic linkage

• It is insoluble in water and cannot be digested in carnivorous animals and humans, but is important in stimulating peristaltic movement

• In herbivorous animals, there are microorganisms that have enzymes that can attack the β linkage, producing cellobiose on hydrolysis

Properties of Monosaccharides and Sugar Derivatives

• Effect of acid: Phosphoric acid forms ester with glucose, while sulphuric acid removes water from monosaccharides, giving a substance called furfural or hydroxyl methyl furfural

• Oxidation:

  • Oxidation of aldhyde group produces aldonic acid (e.g., glucose gives gluconic acid)
  • Oxidation of last alcoholic group produces uronic acid (e.g., glucose gives glucuronic acid)
  • Oxidation of both aldhyde and alcoholic groups produces saccharic acid (e.g., glucose gives glucaric acid)

• Reduction:

  • Production of sugar alcohols: sorbitol, mannitol, xylitol, ribitol, and inositol
  • Inositol is a cyclic alcohol derived from glucose, present in muscle, and is a member of vitamin B-complex