Polysaccharide - definition, examples, function and structure (2023)

Polysaccharide Definition

A polysaccharide is a large molecule made up of manymonosaccharides. Monosaccharides are simple sugars, like glucose. Special enzymes join these tiny monomers together to create large sugar polymers, or polysaccharides. A polysaccharide is also calledglycan. A polysaccharide can be ahomopolysaccharide, where all monosaccharides are the same, or oneheteropolysaccharidein which the monosaccharides vary. Depending on which monosaccharides are connected and which carbons of the monosaccharides are connected, polysaccharides take a variety of forms. A molecule with a linear chain of monosaccharides is called a linear polysaccharide, while a chain that has arms and loops is known as a branched polysaccharide.

Functions of a polysaccharide

Depending on their structure, polysaccharides can have a wide variety of functions in nature. Some polysaccharides are used to store energy, some to send cellular messages, and others to provide support to cells and tissues.

energy storage

Many polysaccharides are used to store energy in organisms. While energy-producing enzymes only work on monosaccharides stored in a polysaccharide, polysaccharides are normally folded and can contain many monosaccharides in a dense area. Also, because the side chains of monosaccharides form as many hydrogen bonds as possible with themselves, water cannot penetrate the molecules, making themhydrophobic. This property allows the molecules to stick together and not dissolve in the cytosol. This reduces the concentration of sugar in a cell and more sugar can be absorbed. Polysaccharides not only store energy, but also allow for changes in the concentration gradient, which can influence cellular uptake of nutrients and water.

cellular communication

Many polysaccharides are convertedglycoconjugateswhen covalently bound to proteins or lipids. Glycolipids and glycoproteins can be used to send signals between and within cells. Proteins destined for a specific organelle can be "tagged" by certain polysaccharides that help the cell move towards a specific organelle. Polysaccharides can be identified by special proteins, which then help attach the protein, vesicle, or other substance to a microtubule. The system of microtubules and associated proteins within cells can carry any substance to its destination location once tagged by specific polysaccharides. Additionally, multicellular organisms have immune systems that are driven by the recognition of glycoproteins on the surface of cells. The cells of a single organism will produce specific polysaccharides to adorn its cells. When the immune system recognizes other polysaccharides and different glycoproteins, it goes into action and destroys the invading cells.

Mobile support

By far one of the main functions of polysaccharides is that of support. All plants on Earth are sustained, in part, by the polysaccharidecellulose. Other organisms, such as insects and fungi, usechitinto support the extracellular matrix around your cells. A polysaccharide can be mixed with any number of other components to create stiffer fabrics, less stiff fabrics, or even materials with special properties. Between chitin and cellulose, both polysaccharides made from glucose monosaccharides, living organisms create hundreds of billions of tons each year. Everything from the wood of trees to the shells of sea creatures is produced by some form of polysaccharide. By simply rearranging the structure, polysaccharides can change from storage molecules to much stronger fibrous molecules. The ring structure of most monosaccharides aids in this process, as seen below.

Structure of a polysaccharide

All polysaccharides are formed by the same basic process: monosaccharides are connected viaglycosidic bonds. When in a polysaccharide, the individual monosaccharides are known aswaste. Below are just a few of the many monosaccharides created in nature. Depending on the polysaccharide, any combination of them can be combined in series.

The structure of the molecules that are combined determines the structures and properties of the resulting polysaccharide. The complex interaction between its hydroxyl (OH) groups, other side groups, the configurations of the molecules, and the enzymes involved affect the resulting polysaccharide produced. A polysaccharide used for energy storage will give easy access to monosaccharides while maintaining a compact structure. A polysaccharide used as a scaffold is usually assembled as a long chain of monosaccharides, which acts as a fiber. Many fibers together produce hydrogen bonds between the fibers that strengthen the overall structure of the material, as seen in the image below.

Glycosidic bonds between monosaccharides consist of an oxygen molecule linking two carbon rings. The bond is formed when a hydroxyl group is lost from the carbon of one molecule, while the hydroxyl group of another monosaccharide loses hydrogen. The carbon of the first molecule will replace the oxygen of the second molecule as its own and the glycosidic bond will be formed. As two hydrogen molecules and one oxygen molecule are expelled, the reaction also produces a water molecule. This type of reaction is calleddehydration reactionas water is removed from the reactants.

Examples of a polysaccharide

Cellulose and Chitin

Cellulose and chitin are structural polysaccharides consisting of many thousands of glucose monomers combined into long fibers. The only difference between the two polysaccharides is the side chains attached to the carbon rings of the monosaccharides. In chitin, the glucose monosaccharides were modified with a group containing more carbon, nitrogen, and oxygen. The side chain creates a dipole, which increases hydrogen bonding. While cellulose can produce hard structures like wood, chitin can produce even harder structures like bark, limestone, and even marble when compressed.

Both polysaccharides form long linear chains. These chains form long fibers, which lie outside the cell membrane. Certain proteins and other factors help the fibers intertwine into a complex shape, which is held in place by hydrogen bonding between the side chains. Therefore, simple glucose molecules that were previously used for energy storage can be converted into molecules with structural rigidity. The only difference between structural polysaccharides and storage polysaccharides is the monosaccharides used. By changing the configuration of glucose molecules, instead of a structural polysaccharide, the molecule will branch and store many more links in a smaller space. The only difference between cellulose and starch is the glucose configuration used.

glycogen and starch

Probably the most important storage polysaccharides on the planet, glycogen and starch, are produced by animals and plants, respectively. These polysaccharides form from a central starting point and spiral outward due to their complex branching patterns. With the help of various proteins that bind to individual polysaccharides, the large branched molecules are formed.granulesor groupings. This can be seen in the image below of the glycogen molecules and associated proteins seen in the middle.

When a glycogen or starch molecule is broken down, the responsible enzymes start at the ends furthest from the center. This is important as you will notice that due to the extensive branching, there are only 2 starting points but many endings. This means that the monosaccharides can be quickly extracted from the polysaccharide and used for energy. The only difference between starch and glycogen is the number of branches that are produced per molecule. This is caused by different parts of the monosaccharides forming bonds and different enzymes acting on the molecules. In glycogen, a branch occurs every 12 or more residues, while in starch a branch occurs only after every 30 residues.

  • monosaccharide– The smallest unit of sugar molecules, or a sugar monomer.
  • monomer– A single entity that can be combined to form a larger entity, or polymer.
  • Polymer– Includes proteins, polysaccharides, and many other existing molecules of smaller combined units.
  • Polypeptide– A polymer of amino acid monomers, also called a protein.


1. If you haven't brushed your teeth for a while, you may notice yellow plaque starting to form. Part of the plaque consists of dextrans, or polysaccharides, which are used by bacteria to store energy. Where do bacteria get the monosaccharides to create these polysaccharides?
A.They synthesize them from sunlight.
B.They create them from your genetic code.
C.They collect them from the food scraps you eat.

Answer to question #1

Cthis right. Every time you eat a little, you get pieces of food between your teeth. There are monosaccharides present in most foods that can feed bacteria and allow them to store energy in dextrans and create plaque. However, the digestive process begins in saliva, and as food remains in the mouth, it continues to release monosaccharides that allow bacteria to grow. That's why it's important to brush and floss regularly.

2. Plants produce both the amylose from starch and the structural polymer of cellulose from glucose units. Most animals cannot digest cellulose. Even ruminants, such as cattle, cannot digest cellulose and rely on internal symbiotic organisms to break down the cellulose bonds. However, all mammals produce amylase, an enzyme that can break down amylose. Why can't amylase break cellulose bonds?
A.Cellulose and amylose are structurally different, and amylase does not recognize cellulose.
B.Cellulose's glycosidic bonds are stronger.
C.The extracellular matrix created by cellulose cannot be broken down.

Answer to question #2

Athis right. Although glucose is used to create both molecules, different configurations are used. In amylose, this causes a dense branching pattern with many exposed spots that can be digested by amylase. Amylase specifically recognizes amylose and cannot bind or break cellulose bonds. In part, this is because the bonds in cellulose are stronger, but not because of the glycosidic bonds. Cellulose exhibits several other linkages not seen in amylose that occur between side chains. This also helps it hold its shape, but it's not impossible to break. Cows spend many hours chewing on their bundle of plant fibers, slowly breaking the bonds between the cellulose molecules.

3. Hyaluronan is a molecule found in vertebrate joints that provides support by creating a gelatinous matrix to cushion the bones. Hyaluronan is created from several different monosaccharides linked together in long chains. Which of the following describes hyaluronan?
1. Homopolisacarideo
2. Saccharide heteropolis
3. Polymer
4. Monomer

A.All of them
B.1, 3
C.2, 3

Answer to question #3

Cthis right. Hyaluronan is a polysaccharide made from different types of monosaccharides, making it a heteropolysaccharide. It is also generally known as a polymer or a molecule made up of monomers. In this case, the monosaccharides are the monomers.


What is the function and structure of a polysaccharide? ›

Polysaccharides are major classes of biomolecules. They are long chains of carbohydrate molecules, composed of several smaller monosaccharides. These complex bio-macromolecules functions as an important source of energy in animal cell and form a structural component of a plant cell.

What is the function of a polysaccharide? ›

Polysaccharides are major classes of biomolecules. They are long chains of carbohydrate molecules, composed of several smaller monosaccharides. These complex bio-macromolecules functions as an important source of energy in animal cell and form a structural component of a plant cell.

What is the definition of a polysaccharide and example? ›

poly·​sac·​cha·​ride -ˈsak-ə-ˌrīd. : a carbohydrate that can be decomposed by hydrolysis into two or more molecules of monosaccharides. especially : one (as cellulose, starch, or glycogen) containing many monosaccharide units and marked by complexity. called also glycan.

What structure do polysaccharides have? ›

Polysaccharides can form spiral, linear fibrous, or branched structures. The individual monosaccharide components of polysaccharides are called residues, and they are connected by glycosidic bonds. The most common examples of polysaccharides are starch, glycogen, and cellulose.

What is the function of polysaccharides quizlet? ›

Polysaccharides are polymers of monosaccharaides linked together by dehydration reactions. they are long chains of sugar units that may function as storage molecules or as structural compounds.

What are 3 polysaccharides and their functions? ›

Three important polysaccharides, starch, glycogen, and cellulose, are composed of glucose. Starch and glycogen serve as short-term energy stores in plants and animals, respectively. The glucose monomers are linked by α glycosidic bonds. Glycogen and starch are highly branched, as the diagram at right shows.

Which of these is an example of a polysaccharide? ›

Starch, cellulose, gum and glycogen are polysaccharides.

What is the structure and function of starch? ›

Starch is made up of long chains of sugar molecules that are connected together. The linear polymer amylose is the most basic form of starch, while amylopectin is the branched form. The primary role of starch is to help plants in storing energy. In an animal's diet, starch is a source of sugar.

What is the structure of the polysaccharide cellulose? ›

The structure of cellulose consists of long polymer chains of glucose units connected by a beta acetal linkage. The graphic on the left shows a very small portion of a cellulose chain. All of the monomer units are beta-D-glucose, and all the beta acetal links connect C # 1 of one glucose to C # 4 of the next glucose.

What is the definition of polysaccharides? ›

(PAH-lee-SA-kuh-ride) A large carbohydrate molecule. It contains many small sugar molecules that are joined chemically.

What is an example of a polysaccharide quizlet? ›

Polysaccharides: More than two monosaccharides joined. Really large, hard to break down. Examples: Starch, Glycogen, cellulose, chitin, peptidoglycan.

What is a polysaccharide simple definition for kids? ›

Polysaccharides are relatively more complex carbohydrates. They are polymers made up of many monosaccharides. They are very large, often branched, molecules. They tend to be amorphous, insoluble in water, and have no sweet taste.

What is the function of the carbohydrates? ›

Carbohydrates play an important role in the human body. They act as an energy source, help control blood glucose and insulin metabolism, participate in cholesterol and triglyceride metabolism, and help with fermentation.

How many structural polysaccharides are there? ›

Structural polysaccharides are of two main types: chitin and cellulose.

What is a primary function of carbohydrates? ›

Carbohydrates, also known as carbs, are vital at every stage of life. They're the body's primary source of energy and the brain's preferred energy source. Carbs are broken down by the body into glucose – a type of sugar. Glucose is used as fuel by your body's cells, tissues, and organs.

What are the functions of polysaccharides A level biology? ›

What are the functions of polysaccharides? Polysaccharides act as storage molecules in both animal and plant cells. They also provide structural support such as cellulose and have a role in cell signalling.

What is the function of polysaccharides in cell wall? ›

Subsequently, we learned that defined fragments of polysaccharides, released from covalent attachment within plant cell walls, can function as regulators of various physiological processes such as morphogenesis, rate of cell growth and time of flowering and rooting, in addition to activating mechanisms for resisting ...

What is the polysaccharide function of energy storage? ›

One of the best known polysaccharides is starch, the main form of energy storage in plants. Glycogen is an even more highly branched polysaccharide of glucose monomers that serves the function of storing energy in animals.

What are the functional classes of polysaccharides? ›

Polysaccharides can be broadly classified into two classes: Homo-polysaccharides – are made up of one type of monosaccharide units. ex: cellulose, starch, glycogen. Hetero-polysaccharides – are made up of two or more types of monosaccharide units.

What are the 4 types of polysaccharides? ›

Types of Polysaccharides

Examples of homopolysaccharides are glycogen, cellulose, starch and insulin. Glycogen is made up of a large chain of molecules and is found in animals and fungi.

What are examples and sources of polysaccharides? ›

  • Cereal foods, cornmeal, pretzels, flours, oats, instant noodles, pasta, rice.
  • Potato, corn.
  • Small amounts in other root vegetables and unripe fruit.

What are 5 functions of starch? ›

In food products, the functional roles of starch could be as a thickener, binding agent, emulsifier, clouding agent or gelling agent.

What is the structure and function of cellulose? ›

Cellulose is the primary structural component responsible for much of the mechanical strength of the cell wall. The distribution and orientation of cellulose microfibrils within the cell wall contribute to the control of cell growth.

What is an example of a function of starch? ›

Starch is a carbohydrate and a natural component of most plants, including fruits, vegetables, and grains. Starchy foods are an essential part of a balanced diet, as they provide energy, fiber, and a sense of fullness. The body breaks down starch molecules into glucose, which is the body's primary fuel source.

What is the structure of glycogen polysaccharides? ›

Glycogen is a polysaccharide that consists entirely of glucose molecules that are linked by two types of bonds - the alpha-1,4-glycosidic bond and the alpha-1,6-glycosidic bond. The alpha-1,4-glycosidic bond is the more common bond and it gives glycogen a helical structure that is suitable for energy storage.

What is the structure and function of cellulose polysaccharide? ›

Cellulose is an organic compound belonging to the category of polysaccharides. It is a polymer made up of glucose subunits. It is found in bacterial and plant cells and is abundantly present in their cell walls. Cellulose plays an important role in the structure and strength of plants.

What is the structure and function of monosaccharides? ›

The monosaccharide consists of single unit which contains carbon chain of three to six carbon. They can combine through glycosidic bonds to form larger carbohydrates. The main function of monosaccharide is to produce and store energy. Glucose and fructose are the most available monosaccharide in nature.


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