Polysaccharide

Polysaccharides . They are biomolecules that fall among carbohydrates and are formed by the union of a large number of monosaccharides and fulfill diverse functions, especially energy and structural reserves. Polysaccharides are chains, branched or not, of more than ten monosaccharides.

Polysaccharides are polymers , whose constituent monomers are monosaccharides, which are repetitively linked through glycosidic bonds. These compounds have a very high molecular weight, which depends on the number of residues or monosaccharide units that participate in their structure. This number is almost always indeterminate, variable within certain margins, unlike what happens with informative biopolymers, such as DNA or protein polypeptides , which have a fixed number of pieces in their chain, in addition to a specific sequence.

Summary

[ disguise ]

• 1 Chemical properties
• 2 Functions
• 3 Classification of polysaccharides
  • 1 According to its composition
• 4 See also
• 5 Sources

Chemical properties

Polysaccharides can be broken down, by hydrolysis of the glycosidic bonds between residues, into smaller polysaccharides, as well as disaccharides or monosaccharides. Its digestion within the cells, or in the digestive cavities, consists of a hydrolysis catalyzed by digestive enzymes (hydrolases) generically called glucosidases, which are specific for certain polysaccharides and, above all, for certain types of glycosidic bond. Thus, for example, the enzymes that hydrolyze starch, whose bonds are of the type called α(1->4), cannot decompose cellulose, whose bonds are of the β(1->4) type, although in both cases the monosaccharides are the same. The glycosidases that digest polysaccharides, which may be called polysaccharides, generally break every second bond, thereby releasing disaccharides and letting other enzymes then complete the work.

In the formation of each glycosidic bond, one molecule of water is “left over”, just as in its breakage by hydrolysis a molecule of water is consumed, so in a chain made of n monosaccharides there will be n-1 glycosidic bonds. Starting from the fact that the general formula, not without exceptions, of monosaccharides is: CxH2xOx, it is easy to deduce that polysaccharides will almost always respond to the general formula: Cx(H2O)x–1.

Features

Polysaccharides represent an important class of biological polymers . Its function in living organisms is usually related to structure or storage. Starch is used as a way to store monosaccharides in plants, being found in the forms of amylose and amylopectin (branched) . In animals, glycogen is used instead of starch which is structurally similar but more densely branched. The properties of glycogen allow it to be metabolized more quickly, which adjusts to the active life of animals with locomotion .

Classification of polysaccharides

According to biological function, polysaccharides are classified into the following groups:

• Reserve polysaccharides: The main energy-providing molecule for the cells of living beings is glucose . When it is not broken down in energy catabolism to extract the energy it contains, it is stored in the form of α(1->4) type polysaccharides, represented in plants by starch and in animals by glycogen .
• Structural polysaccharides: These are carbohydrates that participate in the construction of organic structures. Among the most important we have cellulose , which is the main component of the cell wall in plants, and chitin , which plays the same role in fungi , in addition to being the basis of the exoskeleton of arthropods and other related animals.
• Other functions: Most cells of any living being usually have this type of molecules on their cell surface. For this reason, they are involved in cellular recognition phenomena (Example: Major histocompatibility complex, protection against adverse conditions (Example: Polysaccharide capsules in microorganisms or adhesion to surfaces (Example: the formation of biofilms or biofilms, by acting as a kind of glue .

According to its composition

• Homopolysaccharides: They are formed by the repetition of a monosaccharide.
• Heteropolysaccharides: They are formed by pure bodyboarding and the ordered repetition of a disaccharide formed by two different monosaccharides (or, what is the same, by the alternation of two monosaccharides).

Some heteropolysaccharides participate, together with polypeptides (chains of amino acids), in various mixed polymers called pepidoglycans, mucopolysaccharides or proteoglycans. These are essentially structural components of tissues, related to cell walls and extracellular matrices.