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Chemistry And Carbohydrates

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The Chemistry of Carbohydrates

The chemistry of carbohydrates most closely resembles that of alcohol, aldehyde, and ketone functional groups. As a result, the modern definition of a carbohydrate is that the compounds are polyhydroxy aldehydes or ketones. The chemistry of carbohydrates is complicated by the fact that there is a functional group (alcohol) on almost every carbon. In addition, the carbohydrate may exist in either a straight chain or a ring structure. Ring structures incorporate two additional functional groups: the hemiacetal and acetal.

A major part of the carbon cycle occurs as carbon dioxide is converted to carbohydrates through photosynthesis. Carbohydrates are utilized by animals and humans in metabolism to produce energy and other compounds. Carbohydrates are initially synthesized in plants form a complex series of reactions involving photosynthesis. They store energy in the form of starch or glycogen in animals and humans. They provide energy through metabolism pathways and cycles. Carbohydrates also supply carbon for synthesis of other compounds. (Berdanier, Pgs 45-47).

Metabolism occurs in animals and humans after the ingestion of organic plant or animal foods. In the cells a series of complex reactions occurs with oxygen to convert. For example glucose sugar into the products of carbon dioxide and water and energy. This reaction is also carried out by bacteria in the decomposition/decay of waste maters on land and in water.

Combustion occurs when any organic material is reacted or burned in the presence of oxygen to give off the products of carbon dioxide and water and energy. The organic material can be any fossil fuel such as natural gas (methane), oil, or coal. Other organic materials that combust are wood, paper, plastics, and cloth. The whole purpose of both processes is to convert chemical energy into other forms of energy such as heat.

All carbohydrates are made up of units of sugar (also called saccharide units). Carbohydrates that contain only one sugar unit (monosaccharides) or two sugar units (disaccharides) are referred to as simple sugars. Simple sugars are sweet in taste and are broken down quickly in the body to release energy. Two of the most common monosaccharides are glucose and fructose. Glucose is the primary form of sugar stored in the human body for energy. Fructose is the main sugar found in most fruits. Both glucose and fructose have the same chemical formula (C6H12O6). Disaccharides have two sugar units bonded together. For example, common table sugar is sucrose a disaccharide that consists of a glucose unit bonded to a fructose unit. (Honeyman, Pgs. 66-69).

Complex carbohydrates are polymers of the simple sugars. In other words, the complex carbohydrates are long chains of simple sugar units bonded together (for this reason the complex carbohydrates are often referred to as polysaccharides). The potato actually contains the complex carbohydrate starch. Starch is a polymer of the monosaccharide glucose. (Honeyman, Pgs. 66-69).

Starch is the principal polysaccharide used by plants to store glucose for later use as energy. Plants often store starch in seeds or other specialized organs, for example, common sources of starch include rice, beans, wheat, corn, potatoes, etc. When humans eat starch, an enzyme that occurs in saliva and in the intestines called amylase breaks the bonds between the repeating glucose units thus allowing the sugar to be absorbed into the bloodstream. Once absorbed into the bloodstream, the human body distributes glucose to the areas where it is needed for energy or stores it as its own special polymer - glycogen. Glycogen, another polymer of glucose, is the polysaccharide used by animals to store energy. Excess glucose is bonded together to form glycogen molecules, which the animal stores in the liver and muscle tissue as an "instant" source of energy. Both starch and glycogen are polymers of glucose, however starch is a long, straight chain of glucose units, whereas glycogen is a branched chain of glucose units.

Another important polysaccharide is cellulose. Cellulose is yet a third polymer of the monosaccharide glucose. Cellulose differs from starch and glycogen because the glucose units form a two-dimensional structure, with hydrogen bonds holding



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