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How are carbohydrates classified into monosaccharides, disaccharides, oligosaccharides, and polysaccharides?

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A biochemical flowchart shows the metabolic pathways for carbohydrate utilization, including glycolysis, the pentose phosphate pathway, and the tricarboxylic acid (TCA) cycle. The diagram traces the conversion of glucose, fructose, and glycerol through various intermediates, leading to energy production, carbon dioxide release, and biosynthesis of amino acids and porphyrins. Key steps and branches are labeled, with colored boxes highlighting biosynthetic outputs. — Carbohydrate Pathways for the utilization of carbohydrates.

Carbohydrates are classified into four major groups based primarily on the number of simple sugar units they contain.1

Monosaccharides

Monosaccharides, or simple sugars, are the basic building blocks of carbohydrates. They are polyhydroxy aldehydes or ketones that typically contain three to nine carbon atoms, with five or six being the most common. They are classified by their carbon count (e.g., pentoses have five, hexoses have six) and the presence of an aldehyde or keto group.12

Disaccharides

A disaccharide is formed when two monosaccharide molecules are linked together by a glycosidic bond. Common examples include sucrose, lactose, and maltose.13

Oligosaccharides

Oligosaccharides consist of three to six monosaccharide units. They are relatively infrequent in natural sources compared to other carbohydrate classes.1

Polysaccharides

Polysaccharides are large, complex molecules that may contain up to 10,000 monosaccharide units. They are classified as:1
* Homopolysaccharides: Composed of only one type of monosaccharide (e.g., cellulose, starch, glycogen).45
* Heteropolysaccharides: Composed of two or more different types of monosaccharides or sugar derivatives.45