What is a polysaccharide? Definition and explanation

What is a polysaccharide? Definition and explanation

A polysaccharide designates macromolecules formed by the polymerization of simple or healthy carbohydrates. For sugars; the correct word in French is polysaccharide or polyholoside, but usage has consecrated the use of this anglicism. Polysaccharides are biomolecules formed by the union of a large number of monosaccharides.

The polysaccharides carbon belong to hydrate carbon and fulfill various functions, mainly of reserve energy and structural. The main polysaccharides are: starch, glycogen, cellulose and chitin.

Bonds in polysaccharides

The polymers such as the amylose which are formed of a channel linear with α-D- units glucose linked together by α-1,4-glycosidic bonds. Underneath (colored), due to hydrogen bonding , amylose acquires a spiral structure that contains six units of glucose per turn. Bottom right, amylopectin and glycogen both contain branch points linked by α-1,6 bonds. These branching points occur more often in glycogen.

Polysaccharides are polymers whose constituents, monomers, are monosaccharides, which are repeatedly linked by glycosidic bonds. These compounds have a very high molecular weight. This depends on the number of residues or monosaccharide units involved in their structure. This number is almost always unknown, variable within margins, unlike what happens with informative biopolymers, such as polypeptides of DNA or proteins, which have in the chain a fixed number of pieces, and more of a specific sequence.

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Polysaccharides Breakdown

Polysaccharides can be broken down, by hydrolysis of the glycosidic bonds between residues, into smaller polysaccharides. Hydrolysis also produces disaccharides or monosaccharides. Their digestion inside cells or in digestive cavities consists of hydrolysis catalyzed by digestive enzymes ( hydrolases ) generically called glucosidases, specific for certain polysaccharides and especially for certain types of glycosidic bonds. Thus, for example, the enzymes hydrolyzing starch whose bonds are of the α type cannot decompose the cellulose whose bonds are of the β type, although in both cases the monosaccharides are the same. Glucosidases that digest polysaccharides, which can be called polysaccharides, usually break one of the two bonds, thus releasing disaccharides and allowing other enzymes to do the job.


For example, a fucosan is a polysaccharide present in algae of the genus fucus and in certain other brown Phaeophyceae algae and producing fucose by hydrolysis. Physode for the ( corpuscle or) grain of fucose. Fucosan is colorless in water but turns brown or black when exposed to air. (Do not confuse it with fucan or fucoidan.)

The dextrins are midsize glucose polysaccharides. The shine and stiffness imparted to clothes by the starch are due to the presence of dextrins formed during the ironing of the clothes. Due to their wet tackiness, dextrins are used as adhesives on stamps, envelopes and labels; as binders to hold pills and tablets together; and in the form of pastes. Dextrins are easier to digest than starch and therefore are widely used in the commercial preparation of infant foods. Complete hydrolysis of starch gives, in successive stages, glucose: starch → dextrins → maltose→ glucose. In the human body, several enzymes known collectively as amylases sequentially break down starch into usable glucose units.

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