Introduction to Heteropolysaccharides on Vedantu
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
Did You Know?
Heparin is made up of a disaccharide repeating unit which is made up of D-glucuronate sulphate/L-iduronate 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.
Long chains of monosaccharides make up polysaccharides (glycans). A polymeric structure made up of monosaccharides linked together by glycosidic bonds is known as a polysaccharide and they make up a majority of biomass. These Polysaccharides also make up more than 90% of the carbohydrate mass in nature.
Polysaccharides are divided into two categories: Homopolysaccharides and Heteropolysaccharides.
A chain that contains only one type of monosaccharide unit is known as homopolysaccharides, whereas a heteropolysaccharide contains two or more types of monosaccharide units.The Monosaccharides may link in a linear fashion or even branch out into complex formations and this happens in both types of polysaccharides. Unlike proteins, the Polysaccharidesdo not have any fixed molecular weight. This variation is said to be due to the differences in polysaccharide assembly mechanisms. Without the use of a template, thePolysaccharide synthesis is carried out, and these depend on the intrinsic properties of enzymes.
The polysaccharides that contain multiple monosaccharide units are known as Heteropolysaccharides. Many naturally occurring heteropolysaccharides contain peptides, proteins, and lipids and these are attached to them. Some examples of heteropolysaccharides:i) Peptidoglycans, ii) Agarose, and iii) Glycosaminoglycans (GAGs).
Peptidoglycan (murein) is a part of the bacterial cell wall which is found on the outside of almost all of the bacteria's cytoplasmic membrane. The primary role of the Peptidoglycan is to be able to maintain cell integrity by resisting turgor. This is made up of linear polysaccharide strands which are connected together by short peptides.
Agarose is a natural heteropolysaccharide and you can get it from red seaweed. It is a structural part of their cell wall. A linear polymer made up of agarose repeating units is what Agarose is.
Agarose is ideal for the electrophoretic separation of DNA and RNA molecules in biochemistry experiments and this is due to it’s gel-forming property.
Heteropolysaccharides that are only present in animals and bacteria and not in plants are known as Glycosaminoglycans, and are found in the extracellular matrix (ECM), which binds cells together in tissues in order to provide a pathway for the nutrients and oxygen to reach individual cells in the case of multicellular animals.
Some examples of Homopolysaccharide are: starch, glycogen, chitin, cellulose, and dextran.
Cellulose is the most common biomaterial on the earth. Plants produce cellulose in a majority of cases, but bacteria can also produce it. The tough, fibrous, water-insoluble polysaccharide found mostly in plant cell walls is known as Cellulose and it is important for maintaining the structural integrity of the cell walls of plants. Cellulose is a -D-glucose homopolymer with -1,4 linkages.
FAQs on Heteropolysaccharides
1. What is a heteropolysaccharide?
A heteropolysaccharide is a type of complex carbohydrate, or polysaccharide, that is composed of two or more different types of monosaccharide units or their derivatives. These monomer units are linked together by glycosidic bonds to form long, often branched chains. Unlike homopolysaccharides which have a single repeating monomer, the variation in monomers gives heteropolysaccharides a wide range of complex structures and biological functions.
2. What is the main difference between a homopolysaccharide and a heteropolysaccharide?
The primary difference lies in their monomeric composition. Homopolysaccharides consist of only one type of monosaccharide unit repeated throughout the polymer (e.g., starch and cellulose are made only of glucose). In contrast, heteropolysaccharides are built from two or more different types of monosaccharide units. This structural difference leads to functional diversity, with homopolysaccharides typically serving storage or structural roles, while heteropolysaccharides are involved in more specialised functions like lubrication, cell recognition, and anticoagulation.
3. What are some important examples of heteropolysaccharides and their functions?
Some key examples of heteropolysaccharides include:
- Hyaluronic Acid: Found in connective tissues, synovial fluid, and the vitreous humour of the eye. It acts as a lubricant and shock absorber.
- Heparin: A well-known natural anticoagulant that prevents blood clotting. It is found in mast cells, liver, and lungs.
- Chondroitin Sulfate: A major component of cartilage, providing resistance to compression.
- Bacterial Cell Walls (Peptidoglycan): A polymer of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) units, providing structural integrity to bacterial cells.
4. What is hyaluronic acid and why is it considered a heteropolysaccharide?
Hyaluronic acid is a glycosaminoglycan, a major type of heteropolysaccharide. It is classified as a heteropolysaccharide because its structure is built from a repeating disaccharide unit. This unit consists of two different monosaccharide derivatives: D-glucuronic acid and N-acetyl-D-glucosamine, linked together by alternating β-(1→4) and β-(1→3) glycosidic bonds. Since it contains more than one type of monomeric unit, it perfectly fits the definition of a heteropolysaccharide.
5. What is heparin and what is its primary biological role?
Heparin is a highly sulfated heteropolysaccharide belonging to the glycosaminoglycan family. Its structure is complex, composed of repeating disaccharide units of a uronic acid (like L-iduronic acid or D-glucuronic acid) and a glucosamine derivative. Its primary biological role is as a powerful anticoagulant. It works by binding to and activating antithrombin III, a protein that inactivates thrombin and other clotting factors, thus preventing the formation of blood clots.
6. What are glycosaminoglycans (GAGs) and why are they a major class of heteropolysaccharides?
Glycosaminoglycans, or GAGs (also known as mucopolysaccharides), are long, unbranched heteropolysaccharides consisting of a repeating disaccharide unit. This repeating unit typically contains an amino sugar (like N-acetylglucosamine or N-acetylgalactosamine) and a uronic acid (like glucuronic acid or iduronic acid). They are a major class because many prominent heteropolysaccharides, including hyaluronic acid, heparin, and chondroitin sulfate, belong to this group and play critical roles in the extracellular matrix and connective tissues.
7. Why are heteropolysaccharides structurally more complex than homopolysaccharides?
The structural complexity of heteropolysaccharides arises from several factors that are absent in homopolysaccharides. Firstly, the presence of multiple types of monomers allows for varied sequences and chemical properties along the chain. Secondly, these monomers can be linked by different types of glycosidic bonds (e.g., α-1,4 or β-1,3), and the potential for branching is often greater and more irregular. This combination of different units, linkages, and branching patterns creates a vast array of unique three-dimensional structures, which is essential for their specialised biological functions.
8. How does the presence of different monomer units in heteropolysaccharides contribute to their diverse biological functions?
The variety of monomers directly dictates function. For instance, the presence of negatively charged groups like sulfate (–SO₄²⁻) and carboxyl (–COO⁻) groups in GAGs like heparin and hyaluronic acid makes them highly hydrophilic. This allows them to attract and hold large amounts of water, making them excellent lubricants and shock absorbers. The specific sequence of monomers can also act as a recognition site for proteins, enabling functions in cell adhesion, signalling, and binding to growth factors, a level of specificity not typically seen with simple, repeating homopolysaccharides.
9. Why is chitin classified as a homopolysaccharide, even though its monomer is a modified sugar?
This is a common point of confusion. Chitin is classified as a homopolysaccharide because it is a polymer made of a single, repeating monomer unit. That specific monomer is N-acetyl-D-glucosamine. Although N-acetyl-D-glucosamine is a derivative (a modified version) of glucose, it is the *only* type of unit in the entire chitin chain. The definition of a homopolysaccharide is based on having one repeating monomer type, regardless of whether that monomer is simple or modified. A heteropolysaccharide must contain at least two *different* types of monomers.
