Functions of Polysaccharides (A-level Biology)
What are the Functions of Polysaccharides?
Polysaccharides are involved in various key processes important in the maintenance of homeostasis in an organism.
Starch
- Starch is the key energy store in plants. Most living organisms obtain their energy from glucose. Excess amounts of glucose can be stored in the form of starch, which can later be broken down by a cell to obtain energy.
- Starch is made from amylose and amylopectin. The major starch that we will be concerning ourselves with is a carbohydrate that is actually made up of two polysaccharides of α-glucose: amylose and amylopectin.
- Starch is only found in plants. It is important to note that starches are only found in plants, not animals.
- Starch is insoluble. This is also an adaptation for storage, because starch does not alter the water potential of cells. If it did, there could be an influx of water down an osmotic gradient, making cells swell (and even burst!).
Amylose
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- Amylose has a structure adapted for compact storage.
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- Amylose is an unbranched chain of α-glucose. Amylose is unbranched, and exists in a coiled helical structure, which gives it an overall cylindrical shape.
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- Amylose is compact and easy to store. The purpose of this structure is simply because it allows the amylose to be neatly compacted, thereby allowing cells to store larger amounts of amylose.
- Amylose is compact and easy to store. The purpose of this structure is simply because it allows the amylose to be neatly compacted, thereby allowing cells to store larger amounts of amylose.
Amylopectin
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- Amylopectin has a structure adapted for fast breakdown.
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- Amylopectin is a branched chain of α-glucose. Unlike amylose, amylopectin is not in a helical structure, but instead exists as a long chain with branches extending outwards along the backbone.
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- Amylopectin is easy to break down. The branched structure means that the glycosidic bonds are much more readily available to various enzymes, which break down these branches in order to release glucose for respiration.
Glycogen
- Glycogen is a key energy store in animals. Whilst starch is the key energy store in plants, glycogen is the key energy store in animals.
- Glycogen also consists of α-glucose. Excess α-glucose molecules can be linked together to form very long polymers of glycogen.
- Glycogen is stored in the liver. Glycogen is typically stored in the liver. When energy levels in an organism run low, signals produced by the hypothalamus in the brain can activate the production of certain endocrine hormones which trigger the release and breakdown of glycogen into glucose. This glucose is then utilised by cells during cellular respiration in order to obtain energy.
- Glycogen has a structure adapted for storage and fast breakdown. Glycogen has more branches than amylopectin, and therefore can easily be broken down. Glycogen is also compact, like starch.
Cellulose
So far, the two carbohydrates which we have discussed (starch and glycogen) have primary been involved in energy processes and are made up of α-glucose.
- Cellulose is made from β-glucose. Monomers of β-glucose form very strong chains held together by glycosidic bonds, which result in the formation of long cellulose chains
- Cellulose is found in plant cell walls. Cellulose primarily functions as a structural support for plant cells and is found primarily in plant cell walls.
- Cellulose is unique to plants. Just like starch.
- Cellulose is adapted to be strong. The β-glucose cellulose chains are very tough and are able to form very strong fibres called microfibrils. This makes plant cell walls strong.
FAQs
Polysaccharides are complex carbohydrates made up of many simple sugars. They play an important role in the human body and are found in food sources such as grains, vegetables, and fruits.
Polysaccharides are complex carbohydrates that are made up of long chains of monosaccharide units. They play important roles in many biological processes and have several key functions, including:
Energy storage: Polysaccharides such as starch and glycogen are used by plants and animals, respectively, as a way to store glucose for energy. These polysaccharides are broken down into glucose molecules when energy is needed.
Structural support: Some polysaccharides, such as cellulose, chitin, and peptidoglycan, are used by organisms to provide structural support. Cellulose is the main component of plant cell walls, while chitin is found in the exoskeletons of insects and crustaceans, and peptidoglycan is a component of bacterial cell walls.
Cell signaling and recognition: Polysaccharides such as glycosaminoglycans and glycoproteins are involved in cell signaling and recognition. These molecules are often found on the surface of cells and help cells communicate with each other, as well as with other molecules in the body.
Water absorption and retention: Polysaccharides such as hyaluronic acid and chondroitin sulfate are important for absorbing and retaining water in the body. They are found in connective tissues, such as cartilage and skin, and help to keep these tissues hydrated and flexible.
Fiber for digestion: Polysaccharides such as dietary fiber are important for maintaining digestive health. Fiber cannot be digested by the body, but it helps to regulate digestion and promote the growth of beneficial bacteria in the gut.
Starch is a common example of a polysaccharide. It is found in foods such as potatoes, rice, and bread.
Glycogen is a polysaccharide that is stored in the liver and muscles. It serves as a reserve source of energy for the body, providing quick energy when needed.
Cellulose is a polysaccharide that makes up the cell walls of plants. It is not digestible by humans but provides fiber, which helps regulate digestion and maintain a healthy gut.
The structure of polysaccharides affects their function because it determines how they are broken down and used by the body. Polysaccharides with a linear structure are easier to break down and are used more quickly as energy, while those with a branched structure are more complex and take longer to digest.
Polysaccharides differ from other carbohydrates in that they are made up of many simple sugars, while other carbohydrates like glucose and fructose are single sugars. The number of simple sugars in a polysaccharide affects its structure, function, and how it is used by the body.
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