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The structure and function of carbohydrates.

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Introduction

The structure and function of carbohydrates Carbohydrates are a widely diverse group of compounds that are common in nature. Chemically, carbohydrates are molecules that are composed of carbon, along with hydrogen and oxygen - usually in the same ratio as that found in water (H2O). Typical carbohydrates are composed of strings or chains of monosaccharides - that is, chains of individual sugars. A monosaccharide (mono = one, saccharide = sugar) is the smallest carbohydrate unit. The type of monosaccharides in the chain, length of the chain, and method of linking all determine the composition of the carbohydrate. A listing of some of the saccharides include: * Monosaccharides - single molecules, usually with 5 or 6 carbons * pentoses - sugars with 5 carbons, including arabinose, xylose, ribose * hexoses - sugars with 6 carbons, including glucose, fructose, galactose, mannose ...read more.

Middle

The glucoses in cellulose are linked together differently than starch, that changes the properties of the molecule. Cellulose cannot be digested by enzymes produced by mammals. However, some bacteria do produce cellulase, the enzyme that breaks down cellulose. 4. lignin - the polysaccharide that comprises the woody parts of plants. Cobs, hulls, and the woody portions of trees and shrubs all contain this complex carbohydrate. Lignin is largely indigestible and is therefore unavailable to animals. Some classify lignin in a separate category of compounds due to the complexity of the chemical structure. Sugars generally don't exist in nature in linear chains. Instead, they normally exist in a ring structure, which may be in an alpha or beta form, depending on how the ring is formed. ...read more.

Conclusion

The structure of cellulose is similar to that of amylose in starch - that is, linear chains of glucose, except that the glucose molecules are joined by ?-1,4-glucosidic linkages. This linkage is the reason that humans cannot digest cellulose. Lignin is actually a class of compounds that provides the woody structure to cell walls. The characteristics of lignin vary depending on the plant species, maturity and method of determination. However, lignin is clearly important to nutrition, as it is the component that limits digestibility of fiber sources such as hay. Plant cell walls are complex arrangements of cellulose, hemicellulose and lignin. This contributes significantly to the overall digestibility of the fiber. The proportion of each component depends on species and age of the plant. Chemical determination of structural carbohydrates of plants normally includes determination of acid or neutral detergent fiber. ...read more.

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