What makes cellulose so strong

Amylose is the simpler of the types of molecule and is largely linear chains of C1-to-C4 glysosides, several thousand units in length.

Amylopectin is more complex and these molecules are branched using a combination of C1-to-C4 bonds and C1-to-C6 bonds about every 25 glucose units along the chain.

Such large, complex molecules do not dissolve well in water. Glycogen is also made by linking together glucose molecules. Like starch, it is used by animals to store sugar and provide energy. It is similar to amylopectin in structure, but branched with a C1-to-C6 glycosidic bond about every ten glucose units. Click here to. Components of Cells.

The Macromolecules. In the surface chains there is a mixture of the gauche-gauche and gauche-trans conformations with gauche-trans predominant when the cellulose is dry, but less so when it is wet. The trans-gauche conformation at C-6 in the core chains allows O-6 to hydrogen bond to the chain alongside, and also lets it accept an intramolecular hydrogen bond from O-2 of the preceding residue of the same chain.

This hydrogen bond is absent in the surface chains. These differences in hydrogen bonding mean that the surface chains have some freedom to move out of the flat-ribbon conformation. The lack of intramolecular hydrogen bonding in the surface chains also means that they can form more hydrogen bonds to water or adjacent polysaccharides. From the ratio of surface to core chains it is possible to estimate the size of the crystalline units.

The hydrogen bonds are formed between these chains due to hydrogen atoms and hydroxyl groups which firmly hold the chains together. This results in the formation of cellulose microfibrils that are firm and strong.

Cellulose is present in plant cells in the form of cellulose microfibrils. These microfibrils together form polysaccharide or cellulose matrix. Further details of the polysaccharide matrix will be discussed somewhere else in this article. Cellulose differs from the rest of polysaccharides in its properties. The unique properties of cellulose are due to its unique structure. They also depend on the number of glucose subunits present in cellulose.

It has the following properties;. Cellulose is synthesis does not occur in animals. It is limited to only plants or bacteria. The biosynthesis of cellulose in two organisms follow different steps. In plants, cellulose synthesis takes place on special complexes present at the cell membrane called rosette terminal complexes. These complexes are the hexameric transmembrane proteins that are capable of free floatation in the plasma membrane.

They contain at least three cellulose synthase enzymes. These transmembrane rosettes perform two functions; polymerization of glucose residues to form cellulose chain and assembly of cellulose microfibrils. The process of cellulose chain synthesis begins on the cytoplasmic end of the rosette terminal complexes. The cellulose synthase enzymes use glucose residues provided by UDP-glucose. In the first step, glucosephosphate is converted to glucosephosphate in the cytoplasm of plant cells by phosphoglucomutase enzyme.

This step is common in the synthesis of starch, glycogen, and cellulose. The hydrolysis of pyrophosphate makes this step irreversible. It is also the rate-limiting step in cellulose synthesis. Cellulase synthase requires a primer for the synthesis of cellulose chains. The steroid molecule sitosterol-beta-glucoside serves the function of primer in the synthesis of cellulose. The cellulose synthase begins constructing a cellulose chain on primer using glucose residues provided by UDP-glucose molecules.

It joins the glucose residues via beta glycosidic bonds to form a long chain of cellulose releasing UDP molecules. Once a cellulose chain has been elongated to a certain length, the cellulase enzyme present in the cytoplasm cleaves this chain from the primer. In the cell wall, different cellulose chains are arranged parallel to each other and hydrogen bonds are formed among them. This results in the formation of cellulose microfibrils with high tensile strength. Bacteria use the same family of enzymes for cellulose synthesis as used by plants.

However, the bacterial enzymes are encoded by different genes. Another hypothesis is that plants acquired the cellulose synthesis enzymes from bacteria after endosymbiosis. Cellulose is also synthesized by some animals called tunicates. Tunicates are invertebrate animals found in the sea. They have a hard shell that encloses the delicate body of the animal. Cellulose is found in the shell of these animals. The process of cellulose synthesis is also somehow same as in the plants and bacteria.

The structure of cellulose is essentially the same. Understanding the arrangement of cellulose microfibrils and polysaccharide matrix in the cell wall of plants is also important.

We have studied earlier that as the cellulose chains are synthesized, they are exported out of the cell into the cell wall. Here the cellulose chains are arranged in parallel fashion forming hydrogen bonds among themselves. This results in the formation of cellulose microfibrils.