Polysaccharides: The Long Chain of Simple Sugars

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Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide unit bound together by glycosidic linkage. Example: starch, glycogen, cellulose, chitin etc.

Characteristics of polysaccharide

  • On hydrolysis, they yield monosaccharide units which are usually similar.
  • D glucose is the commonest component of polysaccharide.
  • They have high molecular weight.
  • They are usually amorphous, tasteless, nonsugar, insoluble in water.
  • A great majority of carbohydrate of nature occurs in polysaccharide.
  • They do not exhibit any properties of aldehyde or ketone.

Starch

Starch is the most abundant polysaccharide after cellulose. It is a storage product and found in tubers, roots, seeds and other storage organs where it functions as a reserve nutrient for the growth and development of the plant.

Starch content of cereal grains range from 10 to 30% and potatoes from 50 to 70% of dry weight.

Components of starch

Amylose (15-20%) and amylopectin (80-85%) are the two component of starch and these two are polysaccharide themselves.

Source here
Amylose Amylopectin
15-20% of total starch80-85% of total starch
Amylose has a straight chainAmylopectin has a branched chain
Bond among the glucose is 1, 4 typeBoth 1,4 and 1, 6 (to branch out)
Less soluble in waterMore soluble in water
Does not form a gel when hot water is addedForms a gel when hot water is added
Can be hydrolyzed with α amylase and β amylase enzymes completelyCan not be hydrolyzed with α amylase and β amylase enzymes completely
Gives a dark blue or black color when iodine solution is addedGives a reddish brown color when iodine solution is added

 

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