What do cellulose and starch have in common

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. Think about It Why do monosaccharides form ring structures?

Figure 3. Common disaccharides include maltose, lactose, and sucrose. Think about It What are the most biologically important polysaccharides and why are they important? Key Concepts and Summary Carbohydrates , the most abundant biomolecules on earth, are widely used by organisms for structural and energy-storage purposes. Carbohydrates include individual sugar molecules monosaccharides as well as two or more molecules chemically linked by glycosidic bonds.

Monosaccharides are classified based on the number of carbons the molecule as trioses 3 C , tetroses 4 C , pentoses 5 C , and hexoses 6 C. They are the building blocks for the synthesis of polymers or complex carbohydrates. Disaccharides such as sucrose, lactose, and maltose are molecules composed of two monosaccharides linked together by a glycosidic bond.

Polysaccharides , or glycans , are polymers composed of hundreds of monosaccharide monomers linked together by glycosidic bonds. The energy-storage polymers starch and glycogen are examples of polysaccharides and are all composed of branched chains of glucose molecules.

The polysaccharide cellulose is a common structural component of the cell walls of organisms. Other structural polysaccharides, such as N-acetyl glucosamine NAG and N-acetyl muramic acid NAM , incorporate modified glucose molecules and are used in the construction of peptidoglycan or chitin.

Multiple Choice By definition, carbohydrates contain which elements? Carbohydrates contain carbon, hydrogen, and oxygen. Show Answer Answer d. Monosaccharides may link together to form polysaccharides by forming glycosidic bonds.

Like starch in plants, glycogen is found as granules in liver and muscle cells. When fasting, animals draw on these glycogen reserves during the first day without food to obtain the glucose needed to maintain metabolic balance.

Although the percentage of glycogen by weight is higher in the liver, the much greater mass of skeletal muscle stores a greater total amount of glycogen. Glycogen is structurally quite similar to amylopectin, although glycogen is more highly branched 8—12 glucose units between branches and the branches are shorter. When treated with iodine, glycogen gives a reddish brown color. Glycogen can be broken down into its D-glucose subunits by acid hydrolysis or by the same enzymes that catalyze the breakdown of starch.

In animals, the enzyme phosphorylase catalyzes the breakdown of glycogen to phosphate esters of glucose. Cellulose, a fibrous carbohydrate found in all plants, is the structural component of plant cell walls. The largest use of cellulose is in the manufacture of paper and paper products. Like amylose, cellulose is a linear polymer of glucose. This extreme linearity allows a great deal of hydrogen bonding between OH groups on adjacent chains, causing them to pack closely into fibers part b of Figure 5.

As a result, cellulose exhibits little interaction with water or any other solvent. Cotton and wood, for example, are completely insoluble in water and have considerable mechanical strength. Because cellulose does not have a helical structure, it does not bind to iodine to form a colored product.

Cellulose yields D-glucose after complete acid hydrolysis, yet humans are unable to metabolize cellulose as a source of glucose. 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. Starch , a word that comes from old English and means to stiffen , is also a polysaccharide made in plants.