Is cellulose and starch a carbohydrate?

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Starch, cellulose, and glycogen are polysaccharides found in organisms. Starch is found in plants as their major storage form of carbohydrates. Linear chains of starch are called amylose and when branched they are called amylopectin. Glycogen is similar to amylopectin but is highly branched. It is the major carbohydrate storage form in animals and fungi. Cellulose is a linear polysaccharide, which forms hydrogen bonds among several cellulose chains to form a fibrous structure. It is the major component of the cell wall of plants, some algae, and fungi. Thus, the main difference between starch cellulose and glycogen is their role in each organism.

Starch and cellulose are two very similar polymers. In fact, they are both made from the same monomer, glucose, and have the same glucose-based repeat units.

There is only one difference. In starch, all the glucose repeat units are oriented in the same direction. But in cellulose, each succesive glucose unit is rotated 180 degrees around the axis of the polymer backbone chain, relative to the last repeat unit.

When material scientists are talking material science talk they say that the glucose units in starch are connected by alpha linkages, and that the glucose units in cellulose are connected by beta linkages.

Does this make any difference? It makes a lot of difference! The most important difference in the way the two polymers behave is this: You can eat starch, but you can't digest cellulose. Your body contains enzymes that break starch down into glucose to fuel your body. But we humans don't have enzymes that can break down cellulose. Some animals do, like termites who eat wood, or cattle who eat grass and break down cellulose in their four-chambered stomachs. So unless you're a termite or a cow, don't try to nourish yourself on woodchips. It's not even good as "fiber" in your diet, sorry to say.

Cellulose is also a lot stronger than starch. Starch is practically useless as a material to make things, but celluose is strong enough to make fibers, and hence rope, clothing and paper products. Cellulose doesn't dissolve in water the way starch does, and certainly doesn't break down as easily. Breaking down or dissolving in water just would be a little too inconvenient for something we use to make clothes and buildings with. It would certainly be embarrassing if a good soaking rain washed away all the wooden houses, park benches, and playground equipment. And what about trees? The forests that we depend on for so many important contributions to our world would melt away in a good downpour. Glad that doesn't happen.

Starches are carbohydrates in which 300 to 1000 glucose units join together. It is a polysaccharide which plants use to store energy for later use. Starch forms in grains with an insoluble outer layer which remain in the cell where it is formed until the energy is needed. Then it can be broken down into soluble glucose units. Starches are smaller than cellulose units, and can be more readily used for energy. In animals, the equivalent of starches is glycogen, which can be stored in the muscles or in the liver for later use.

Foods such as potatoes, rice, corn and wheat contain starch granules which are important energy sources for humans. The human digestive process breaks down the starches into glucose units with the aid of enzymes, and those glucose molecules can circulate in the blood stream as an energy source. Tillery, et al. point out an interesting example of this enzyme-catalyzed breakdown process. If you chew on a piece of bread for a while, it will begin to taste sweet because the enzymes in saliva are already beginning to break down the starch into glucose, a sugar.

Biochemical concepts

Chemistry concepts

Tillery,Enger, Ross
Ch 14.

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 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 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.

(Image will be uploaded soon)

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.

(Image will be uploaded soon)

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.

Parameter

Starch

Cellulose

Background

This word was derived from the German language and it means strength, or to stiffen something.

It was discovered in 1838 from plant matter and was used to produce thermoplastic for the first time.

Glucose Range

Uses about 200-1000 glucose molecules to form one starch molecule.

Takes up 500 glucose molecules to form one starch molecule.

Bonding

Hydrogen bonding

None

Role

To store energy in the form of carbohydrates.

To form a specific structure of plants.

Type of chain

They are coiled and unbranched (amylose) or long, branched (amylopectin).

These are long, straight, unbranched chains forming H-bonds with the adjacent chains.

Solubility in water

Amylose is soluble in water, and amylopectin is insoluble in water.

Insoluble

Forms

Grain form

Fibres form.

Found in

It is found in plants

It is found only in plants (cell walls)

Glucose unit linkages

Starch contains glucose residues as α(1-4) glycosidic bonds in amylose, while glycosidic bonds at branching points in amylopectin α(1-6), otherwise α(1-4) bonds.

Cellulose constitutes their residues of glucose as glycosidic bonds with β(1-4).

Molar mass

The molar starch mass varies

162.1406 g/mol

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.

Is cellulose a carbohydrate?

What type of carbohydrate is starch and cellulose?

What is starch & cellulose?

Is starch is a carbohydrate?