Heteropolysaccharides

Introduction to Heteropolysaccharides

  • Long chains of monosaccharides make up polysaccharides (glycans). A polysaccharide is a polymeric structure made up of monosaccharides linked together by glycosidic bonds. Polysaccharides make up a majority of biomass. Polysaccharides make up more than 90% of the carbohydrate mass in nature.

  • Polysaccharides are divided into two categories: homopolysaccharides and heteropolysaccharides. A homopolysaccharide is classified as a chain that contains only one type of monosaccharide unit, whereas a heteropolysaccharide contains two or more types of monosaccharide units. Monosaccharides may link in a linear fashion or branch out into complex formations in both types of polysaccharides. Polysaccharides, unlike proteins, do not have a fixed molecular weight. This variation is due to differences in polysaccharide assembly mechanisms. Polysaccharide syntheses are carried out without the use of a template and depend solely on the intrinsic properties of enzymes.

In this article, we will study Heteropolysaccharides, heteropolysaccharides examples, and homopolysaccharides and heteropolysaccharides examples in detail.


Detailed Study of Homopolysaccharides and Heteropolysaccharides Examples


Heteropolysaccharides

Heteropolysaccharides are polysaccharides that contain multiple monosaccharide units. Many naturally occurring heteropolysaccharides have peptides, proteins, and lipids attached to them.  Some heteropolysaccharides examples are:

1) Peptidoglycans 

2) Agarose

3) Glycosaminoglycans (GAGs)


1. Peptidoglycan

Peptidoglycan (murein) is a part of the bacterial cell wall found on the outside of almost all bacteria's cytoplasmic membrane. Its primary role is to maintain cell integrity by resisting turgor.

Peptidoglycan is made up of linear polysaccharide strands that are connected together by short peptides.

The polysaccharide strands are made up of 1,4 glycosidic linkages that connect alternating N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc) residues. GlcNAc and MurNAc are linear polymers that are crosslinked in the cell wall by short peptides whose exact structure varies depending on the bacterial species.

By hydrolyzing -1,4 linkages between GlcNAc and MurNAc, the enzyme lysozyme destroys bacteria. Tears contain lysozymes, which function as a bacterial defence mechanism. Penicillin and related antibiotics destroy bacteria by blocking the formation of crosslinks, causing the cell wall to become too fragile to withstand osmotic lysis.

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2. Agarose 

Agarose is a natural heteropolysaccharide derived from red seaweed, and it is a structural part of their cell wall.

Agarose is a linear polymer made up of agarbiose repeating units. D-galactose (-D-glalactopyranose) and L-galactose derivative (3,6-anhydro—L-galactopyranose) are connected together by -1,4 glycosidic linkages to form agarbiose. Agarbiose units are linked together by a -1,3 glycosidic linkage to form a polymer with 600-700 residues. An ether bridge connects C3 and C6 in the 3,6-anhydro—L-galactopyranose residue. A sulphate ester at the C2 position can be found in a small percentage of 3,6-anhydro—L-galactopyranose residues.

Agarose is purified from agar or derived from red seaweed that produces agar. Agarose and agaropectin are the two main components of agar.

The remarkable gel-forming property of agarose makes it ideal for the electrophoretic separation of DNA and RNA molecules in biochemistry experiments.

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3. Glycosaminoglycans

Glycosaminoglycans are heteropolysaccharides that are only present in animals and bacteria and not in plants. Glycosaminoglycans are found in the extracellular matrix (ECM), which binds cells together in tissues and provides a porous pathway for nutrients and oxygen to reach individual cells in multicellular animals.

Glycosaminoglycans are a type of linear polymer made up of disaccharide units that repeat. They're a kind of complex carbohydrate that includes amino sugars as well as uronic acids. N-Acetylglucosamine or N-acetylgalactosamine is one of the two monosaccharides, whereas the other is normally a uronic acid, such as D-glucuronic or Liduronic acid. Hyaluronic acid, chondroitin sulphate, heparin, and keratin sulphate are examples of glycosaminoglycans.


Homopolysaccharide 

Homopolysaccharide examples are starch, glycogen, chitin, cellulose, and dextran. Some of them are explained below:


1. Starch

A homopolysaccharide, starch is made up of glucose monomer units linked together by glycosidic linkage. Plant cells' starch is the most essential storage polysaccharide or nutrient reservoir. The starch molecules are found in large clusters or granules within the plant cells. Humans consume more than half of their carbohydrates in the form of starch. Amylose and amylopectin are two types of starch that are both made up of glucose monomers.


2. Glycogen

Animal cells' primary storage polysaccharide molecule is glycogen. Glycogen is structurally similar to amylopectin; the only difference is the degree of branching. In comparison to amylopectin, glycogen is highly branched, with a new branch emerging from the glycogen chain every 8-12 residues. The polymer of -D-glucose bound by glycosidic linkage (α-1, 4) is known as glycogen. (α-1, 6) linkage exists at the branching point.


3. Cellulose

One of the most common biomaterials on the earth is cellulose. Plants produce it in the majority of cases, but bacteria may also produce it. Cellulose is a tough, fibrous, water-insoluble polysaccharide found mostly in plant cell walls. It is important for maintaining the structural integrity of plant cell walls. Cellulose is a -D-glucose homopolymer with -1,4 linkages. The cellulose molecule, like amylose, is a linear, unbranched homopolysaccharide made up of 10,000-15,000 million -D-glucose units linked together by glycosidic linkage.


Difference Between Homopolysaccharides and Heteropolysaccharides

Homopolysaccharides

Heteropolysaccharides

They are chemical compounds that are made up of a single type of monomer.

They are compounds that are made up of two or more different types of monomer.

Made up of the same repeating unit.

Made up of the different repeating unit.

A single type of monomer is involved.

Different types of monomer are involved.

They are simple structures compared to heteropolysaccharide.

They are complex structures.


Did You Know?

Heparin is made up of a disaccharide repeating unit which is made up of D-glucuronate sulphate/L-idurunote sulphate and N-sulphoglucosamine –6-sulfate linked by 1,4 glycosidic bonds. A -1,4 linkage links the disaccharide units together.

It can be found in the liver, lungs, spleen, and monocytes, among other places. Heparin is primarily made from animal lung tissues in commercial preparations. It is an anticoagulant that is often used in clinical trials when taking blood in vitro. It is also used to prevent intravascular coagulation in humans. Antithrombin binds to and inhibits thrombin, a protease that is required for blood clotting.

FAQs (Frequently Asked Questions)

Question: Is Chitin a Heteropolysaccharide?

Ans: Chitin is a homopolysaccharide (polysaccharide). This simply means that it is made up of repeating units of the same monosaccharide, which is N-acetylglucosamine in this case. Glycogen and cellulose are two other homopolysaccharides. The monosaccharide units in a heteropolysaccharide are made up of several different monosaccharide units.

Question: Is Hyaluronic Acid a Heteropolysaccharide?

Ans: Heteropolysaccharides are polysaccharides whose molecules are made up of various types of monosaccharides. Hyaluronic acid is a heteropolysaccharide since it is made up of thousands of alternate units of N-acetyl glucosamine and glucuronic acid.

Question: Is it True that Glycogen is Lost Overnight?

Ans: Though muscle glycogen levels do not significantly decrease overnight, the brain's demand for glycogen as a fuel depletes liver glycogen. Due to the brain's 0.1 g/min, glucose consumption rate at nighttime is fast, it will deplete the liver's glycogen storage from 90 to 20 grams.