What do cellulose molecules consist of

Cellulose: Beta glucose is the monomer unit in cellulose. As a result of the bond angles in the beta acetal linkage, cellulose is mostly a linear chain.

Starch: Alpha glucose is the monomer unit in starch. As a result of the bond angles in the alpha acetal linkage, starch-amylose actually forms a spiral much like a coiled spring. Dietary fiber is the component in food not broken down by digestive enzymes and secretions of the gastrointestinal tract.

This fiber includes hemicelluloses, pectins, gums, mucilages, cellulose, all carbohydrates and lignin, the only non-carbohydrate component of dietary fiber.

High fiber diets cause increased stool size and may help prevent or cure constipation. Cereal fiber, especially bran, is most effective at increasing stool size while pectin has little effect.

Lignin can be constipating. Fiber may protect against the development of colon cancer, for populations consuming high fiber diets have a low incidence of this disease. The slow transit time between eating and elimination associated with a low fiber intake would allow more time for carcinogens present in the colon to initiate cancer. But constipated people do not have a higher incidence of colon cancer than fast eliminators, so fiber's role in colon cancer remains unclear.

Dietary fiber may limit cholesterol absorption by binding bile acids. Note in these cyclic structural diagrams, the carbon atoms composing the ring are not explicitly shown. Two monosaccharide molecules may chemically bond to form a disaccharide. The name given to the covalent bond between the two monosaccharides is a glycosidic bond.

Glycosidic bonds form between hydroxyl groups of the two saccharide molecules, an example of the dehydration synthesis described in the previous section of this chapter:. Common disaccharides are the grain sugar maltose , made of two glucose molecules; the milk sugar lactose , made of a galactose and a glucose molecule; and the table sugar sucrose , made of a glucose and a fructose molecule Figure 3.

Polysaccharides, also called glycans , are large polymers composed of hundreds of monosaccharide monomers. Unlike mono- and disaccharides, polysaccharides are not sweet and, in general, they are not soluble in water. Like disaccharides, the monomeric units of polysaccharides are linked together by glycosidic bonds.

Polysaccharides are very diverse in their structure. Three of the most biologically important polysaccharides— starch , glycogen , and cellulose —are all composed of repetitive glucose units, although they differ in their structure Figure 4.

Cellulose consists of a linear chain of glucose molecules and is a common structural component of cell walls in plants and other organisms. Glycogen and starch are branched polymers; glycogen is the primary energy-storage molecule in animals and bacteria, whereas plants primarily store energy in starch. The orientation of the glycosidic linkages in these three polymers is different as well and, as a consequence, linear and branched macromolecules have different properties.

Modified glucose molecules can be fundamental components of other structural polysaccharides. Examples of these types of structural polysaccharides are N-acetyl glucosamine NAG and N-acetyl muramic acid NAM found in bacterial cell wall peptidoglycan. Polymers of NAG form chitin , which is found in fungal cell walls and in the exoskeleton of insects. Figure 4. Starch, glycogen, and cellulose are three of the most important polysaccharides.

In the top row, hexagons represent individual glucose molecules. Micrographs bottom row show wheat starch granules stained with iodine left , glycogen granules G inside the cell of a cyanobacterium middle , and bacterial cellulose fibers right.

Chitin is a structural polymer found in cell walls of fungi and exoskeletons of some animals. Skip to main content. Microbial Biochemistry. Search for:. Carbohydrates Learning Objectives Give examples of monosaccharides and polysaccharides Describe the function of monosaccharides and polysaccharides within a cell.

Sometimes known as glycans , there are three common and principal types of polysaccharide, cellulose, starch and glycogen , all made by joining together molecules of glucose in different ways.

This molecule is synthesized, stored, modified and used as a building material by plants. It is certainly the most abundant of all the polysaccharides. In the cellulose molecule the individual glucose monosaccharides are all linked to one another in the form of a long, long, linear chain.

The carbon atom number 1 C1 in one sugar is linked to the fourth carbon atom C4 of the next sugar in an extended array. All the glucose molecules in cellulose have the beta-configuration at the C1 atom, so all the glycosidic bonds that join the glucose molecules together are also of the beta type. This means that the cellulose molecule is straight, and many such molecules can lay side by side in a parallel series of rows. Tiny forces called hydrogen bonds hold the glucose molecules together, and the chains in close proximity.

Although each hydrogen bond is very, very weak, when thousands or millions of them form between two cellulose molecules the result is a very stable, very strong complex that has enormous strength.