An introduction to Starch and Cellulose
Polysaccharides are the most abundantly available in nature among carbohydrates and perform a variety of functions, such as energy storage or as components of plant cell walls. Polysaccharides are very large polymers made up of tens to thousands of monosaccharides, linked by glycosidic linkages. Common polysaccharides: Starch, glycogen, and cellulose.
Heteropolymers can include, in addition to monosaccharides, sugars, amino sugars, or non-carbohydrate substances. Heteropolymers are common in nature and are non reducing carbohydrates (with no sweet taste).
Starch
Starch is a glucose polymer in which all repeat units are directed in one direction and connected by alpha bonds. Starch is edible and can be eaten safely by humans as we have the enzymes which can break it down into glucose.
It is a grain, with the main source for starch being potatoes, wheat, corn, and rice. These carbohydrates are broken down into glucose and used as a source of energy and a metabolism aid when reaching our bodies.
Starch is less crystalline and is weaker than cellulose. Despite the fact that raw starch is not soluble in cold water, it can be dissolved in warm water and can be used in different ways.
It's most commonly used as food but has other uses as well. It can be used as glue, for tightening up clothes and weaving linen, for thickening sauces and for paper treatment.
Cellulose
Cellulose is a glucose polymer whose units can be rotated around the axis of a backbone of glucose unit polymer chains, and are connected by beta links. It is the most natural organic compound and is a fundamental component of plant cells.
While humans can easily consume any type of cellulose, such as the outer shells of corn, the only animals that can digest cellulose are termites and cud-chewing goats, deer, or buffalo because they have some enzymes that can break down cellulose into glucose.
It has many commercial uses and is the main component of the paper and the fibre used to make clothes such as linen and cotton. Cellophane and rayon are also made from cellulose through dissolving the pulp by viscose, causing it to degrade and then dissolve into cellulose xanthate in caustic soda.
Structure of Starch
Starch is made from a chain of α-glucose monomers. The glycosidic bonds are present in its linkage which is formed through the reaction of condensation. Water is released in this reaction. Mainly starch is made up of sugar glucose. Glucose is a molecule made up of carbon (C), hydrogen (H), and oxygen (O) whose basic chemical formula of C6H12O6. An α- glucose monomer structure is drawn below.
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Structure of Cellulose
The successive unit of glucose monomer present in the structure of starch is rotated 180 o around the polymer backbone chain’s axis and cellulose structure is obtained. At high temperatures, cellulose can be broken down into glucose (C6H12O6) by treating with concentrated minerals acids. (C6H10O5)n is the general formula used for cellulose.
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Structural Difference Between Starch and Cellulose
Starch consists of two ingredients-amylose and amylopectin. Amylose is a long linear chain of -D-(+)-glucose units joined by glycosidic association C1-C4 (along-link).
Amylopectin is a branched-chain polymer consisting of ‐D-glucose units in which the chain is formed by glycosidic connection C1-C4 and glycosidic connection C1-C6 branches.
Cellulose, on the other hand, is a straight-chain polysaccharide with β - D-glucose units joined by glycosidic linkage C1-C4 (β-link).
Starch vs Cellulose
There are some parameters to differentiate between starch and cellulose. The difference between starch and cellulose are given below on the basis of parameters.
Starch and cellulose are made from the same monomer i.e. glucose hence they are very similar polymers. As their monomer is the same so they also have the same glucose-based repeat units. Cellulose is comparatively much stronger than starch. Hence cellulose is used for making fibres, clothes, papers, rope etc. while starch is practically not that useful in making things.
FAQs on Difference Between Starch and Cellulose
1. How are Starch and Cellulose similar and different?
Starch and cellulose are two similar polymers commonly occur. In fact, both are made of the same monomer, glucose, and have the same replicate units based on glucose. Only one difference does exist. All glucose-repeat units in starch are oriented in the same direction. The main difference between starch and cellulose is in their linkage because the glucose units in starch are connected by α- linkages, and that the glucose units in cellulose are connected by β- linkages.
2. Why can humans digest starch but not cellulose?
To digest starch is easy for the human body but not cellulose because our body does not contain necessary enzymes that help the digestion of cellulose but there are some enzymes that can digest starch because such enzymes are able to break alpha linkage of starch. Bond cannot be digested by our intestines. The bond is for supporting structure. We do not want to be able to break down our structural support and that is why we need it in our food.
3. Why is cellulose stronger than starch?
They are bound together in cellulose, so that opposite molecule are rotated 180 degrees from one another. This seemingly minor change makes cellulose much stronger than starch since parallel cellulose fibres stack up just like corrugated sheets stacked on top of each other. Cellulose has more hydrogen bonds between adjacent glucose units, both within a chain and between adjacent chains, making it a tougher fibre than glycogen or starch.