“Starch, cellulose and glycogen are all polysaccharides; however they differ in the role they play in living cells. These differences are most likely related to the differences in their structures. What are their uses, and how do their uses relate to their structures?”
Starch, cellulose and glycogen are all polymers of glucose monomers, polysaccharides joined together by dehydration synthesis. All of them play different roles in living cells — starch and cellulose in plant cells cell wall and glycogen in cells of human skeletal muscle and liver and some fungi.
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Starch and glycogen are both made from alpha-glucose, which is an isomer of glucose in which the hydroxyl (-OH) group attached to carbon number 1 is below the plane of the ring.
Starch is used as an energy reserve in plants, it is found commonly in everyday food we consume, such as potatoes, rice and yams. Starch is a polysaccharide carbohydrate consisting of a large number of glucose monosaccharide units joined together by glycosidic bonds. It composed of two kinds of polymer: amylose and amylopectin. Amylase is a helical alpha-glucose chain without branches, with a molecular weight ranging from 4000 to 150000. The several thousands of glucose molecules are joined by alpha-1, 4 glycosidic bonds, held between each glucose unit. Amylopectin, on the other hand, is a branched alpha-glucose chain, with a molecular weight of 500000 or above. It carries alpha-1,6 connecting branches every 24 to 30 glucose residues of the alpha-1,4 linked chain, resulting in a tree or brush-like structure.
It contains up to a million glucose residues which make it among the largest molecules occurring in nature. Starch is the compact of glucose, so a huge amount of glucose units are packed in one glycogen/starch molecule and occupy a small space only, which can be easily broken off by hydrolysis and used as energy. Dehydration synthesis links glucose molecules together with ester bonds (C-O-C).
These bonds are easily broken down by digestive enzymes to provide glucose that is absorbed into our bloodstream as blood sugar. Starch is also relatively insoluble in water and hence will not affect the osmotic balance or diffuse out of the cell, that’s why they are stored as granules in the cytoplasm, without affecting the operation of plant cells.
Glycogen is used as an energy reserve in animals, which is why it is also called animal starch. Glycogen can be described as an “animal equivalent” of amylopectin, with a highly branched structure and has a molecular weight of about 480000. Most of the glucose units are linked by alpha-1,4 glycosidic bonds, approximately 1 in 12 glucose residues also make the alpha-1,6 glycosidic bond with second glucose, which results in the creation of a branch. It is shorter and has more branches when compared to amylopectin, and is more soluble than starch.
The highly branched structure permits the rapid release of glucose from glycogen stores, for example, in muscle cells during exercise. The ability to rapidly mobilize glucose is more essential to animals than to plants. It also shares the advantage of being tightly crammed together, allowing it to be easily broken off by hydrolysis and used as energy while using little spaces. Glycogen is created when there are high blood sugar levels and excess glucose in the body. The pancreas secretes insulin, which stimulates the creation of glycogen from glucose and signals the body to use glucose as its main form of energy.
Cellulose is made from beta-glucose, an isomer of glucose in which the hydroxyl group attached to carbon 1 is above the plane of the ring.
Cellulose is the structural component of the primary cell wall of green plants. It has a much more rigid structure than starch or glycogen, as the glucose monomers are linked by 1, 4 glycosidic bonds of beta-glucose, which produce a very straight chain. the beta-1,4 glycosidic bond is stick outward between each beta-glucose unit, which enables the linkage of hydrogen bond with other beta-glucose units surrounding it, thus the hydrogen bond is actually giving the mechanical strength for cellulose.
It is highly insoluble in water, and most organisms can not produce enzymes to break it down. Cellulose is highly permeable, hence materials are able to move in or out of the cellulose cell wall freely. Beta-glucose unit in cellulose is a parallel array, which there are some microfibrils formed. the space of microfibril also allows materials to move in or out. Lignin deposits on the microfibrils also allow the lignified plant to stand upright.
Humans can’t digest fibre, another name for cellulose, but it is an important part of a healthy diet since it can maintain the shape of feces passing through the digestive tract, allowing it to move smoothly and at a faster rate, which helps to stop too much water being absorbed in the large intestine and so reduces constipation. It also feeds the bacteria in your large intestine, which digests some of the cellulose and other molecules your enzymes can not.
Cellulose is made by the condensation of beta-glucose.
the beta-1,4 glycosidic bond is stuck outward between each beta-glucose unit, this enables the formation of a hydrogen bond with another beta-glucose unit surrounded it,
thus the hydrogen bond is actually giving the mechanical strength for cellulose.
features of cellulose
-> insoluble in water
-> give no change with iodine solution
-> long chain of beta-glucose
-> can be hydrolyzed with suitable enzyme.
Importance of cellulose for plant
-> Cellulose is highly permeable, hence materials are able to move in or out of the cellulose cell wall freely.
-> beta-glucose unit in cellulose is a parallel array, which there are some microfibrils formed. the space of microfibril also allows materials to move in or out.
-> lignin deposits on the microfibrils which allow the lignified plant to stand upright.
The glucose monomers are linked by 1,4 glycosidic bonds. Hydrogen bonds between adjacent cellulose molecules allow them to form strong fibres, which suite them to their role as the main structural component of plant cell walls.
Cellulose is a special kind of carbohydrate. It is insoluble and most organisms can not produce enzymes to break it down. It is found only in plants, and it’s found in the cell wall. It is composed of ï¿½ glucose molecules, which create a more rigid structure when joined than the? links found in energy storage glycogen and starch molecules.
The reason for this is that when you make 1-4 glycosidic bonds with beta glucose it creates a very straight chain. The chains of cellulose lie close to each other so you get hydrogen bonding between the chains. This makes the molecule very stable and highly resistant to breakdown. You are probably wearing cellulose as you sit here and read this. The cotton used to make clothes etc is cellulose from around the seeds of the cotton plant.
Fibre helps the plant keep a strong structure. Humans can’t digest fibre, but it is an important part of a healthy diet because it helps the digestive tract by giving it more to push on. This helps the contents move through at a reasonable rate. It also helps to stop too much water from being absorbed in the large intestine and so reduces constipation. It also feeds the bacteria in your large intestine. These bacteria are not bad, they are good. They can digest some of the cellulose and other molecules your enzymes can not. Half the weight of your poo may be bacteria! But without healthy bacteria you are less likely to have a healthy gut, so keep eating the fibre!
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