Carbohydrates

Introduction

Carbohydrates are so-called because these molecules are made up of carbon atoms ("carbo") bonded to groups of oxygen and hydrogen atoms, called hydroxide groups ("hydrate"). Carbohydrates are a major energy source for living organisms. They also have a structural role. For example, the cell walls in plants and wood are both made of a carbohydrate called cellulose. In fact, most of the weight of plants comes from a carbohydrate of one kind or another. Depending on their structure, they are grouped in families. The simplest sugars, such as glucose, are called monosaccharides. Molecules made up of two monosaccharides bonded together are called disaccharides. The word saccharide comes from the Latin saccharum, meaning "sugar." Molecules made up of more than two monosaccarides are called polysaccharides. Sugars are very soluble in water, as seen when adding a spoonful to a cup of tea.

A large class of organic compounds that includes sugars, starches, and fiber. Carbohydrates contain two hydrogen atoms and one oxygen atom (H2O) for each carbon atom, and the name carbohydrate relates to the apparent "hydrated carbons" in their chemical formulas. Carbohydrates represent such a variety of substances that they are grouped into several categories (Zawadzki, 1854-1859) .

Nutritionally important carbohydrates are categorized as simple and complex, according to their size. Simple carbohydrates are referred to as sugars. Simple carbohydrates in the form of natural sweeteners are among the most common food additives. Examples are sucrose, dextrose, fructose, and corn syrup, as well as any word on a food label that ends in complex carbohydrates occur in plants as starch and fiber.

Nutritionists classify carbohydrates in foods according to their degree of processing. Refined carbohydrates, like sugar and white flour, are highly purified materials, containing little, if any, of the nutrients found in the whole food from which the carbohydrate was prepared; therefore, they supply mainly calories. Carbohydrates are also classified according to size: monosaccharides, dissacharides, oligosaccharides, and polysaccharides. The simplest are monosaccharides, which include simple sugars. The family of hexoses are monosaccharides containing six carbon atoms; glucose and fructose are examples. Pentoses are simple sugars with five carbon atoms; ribose, the raw material for RNA, is the most common example.

Discussion

The predominant carbohydrate of the body is glucose. Glucose in the blood is called blood sugar and is a major fuel source for most cells of the body. The brain relies on glucose to meet its energy needs. Unless the diet supplies adequate carbohydrates, the body's metabolism switches to a starvation mode, in which body fat is burned to meet most energy needs. To fuel the brain during starvation, glucose is synthesized from amino acids obtained by the breakdown of muscles. Disaccharides contain two linked simple sugars. The most familiar is sucrose (table sugar). This disaccharide contains glucose and fructose. Fragments of complex carbohydrates are called oligosaccharides. As an example, food additives like maltodextrin are derived from starch and typically contain 3 to 10 glucose units. Because they are much smaller than starch molecules they are water soluble.

he largest carbohydrates are polysaccharides, which are ...