What constitutes a disaccharide?

A disaccharide is specifically defined as a carbohydrate composed of two monosaccharide units that are linked together by a glycosidic bond. This type of sugar is formed when two simple sugars undergo a dehydration synthesis reaction, resulting in the release of a water molecule and the formation of the bond between them.

Common examples of disaccharides include sucrose, which is formed from glucose and fructose, and lactose, formed from glucose and galactose. The presence of exactly two sugar units is what distinguishes disaccharides from other types of carbohydrates, such as monosaccharides (which consist of a single sugar unit) and polysaccharides (which consist of many sugar units).

Understanding the definition and structure of disaccharides is essential in biochemistry and can help in recognizing their role in nutrition and biological processes.