How is cellulose made

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Unlike starch or glycogen, these chains do not undergo any coiling, helix formation or branching. Rather, these chains are arranged parallel to each other. 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. Polysaccharide matrix is formed when other sugar molecules interact with these cellulose microfibrils. In the primary cell wall of plants, glucans and arabinoxylans are the two major components of the polysaccharide matrix.

These polysaccharides interact with one another and form a network among the cellulose microfibrils. This network is strengthened by cross-links formation. These cross-links are formed when arabinoxylan residues react with acids like ferulic acid FA and diferulic acid DFA. Due to this reason, it is also said that the polysaccharide matrix is made up of acidic polysaccharides.

In addition to the cellulose microfibrils and polysaccharide matrix, the primary cell wall also contains cross-linking polysaccharides. These polysaccharides cross-link the cellulose microfibrils to form a complex network. Most important of these cross-linking polysaccharides is hemicellulose. It is a derivative of cellulose and will be discussed briefly towards the end of this article. Calcium also plays an important role in network formation. It cross-links the acidic polysaccharides present in the polysaccharide matrix.

Cellulose is the most abundantly produced biopolymer on earth. It is present in the cell wall of all plant cells. Cellulose is also present in the cell wall of other organisms like bacteria and algae. Besides, cellulose is also present in wood obtained from the trees.