What defines a disaccharide?

A disaccharide is defined as two monosaccharides (simple sugars) that are chemically bonded together. This process usually involves a dehydration reaction, where a water molecule is released as the two sugar units combine. Common examples of disaccharides include sucrose, which is composed of glucose and fructose, and lactose, which is formed from glucose and galactose. The unique properties of disaccharides, including their two-sugar structure, differentiate them from polysaccharides, which are large carbohydrate chains, and from monosaccharides, which are single sugar units. Additionally, disaccharides are not proteins, which are made up of amino acids rather than sugars. Understanding the structure and composition of disaccharides is fundamental in biochemistry and nutrition, as they play key roles in energy metabolism in living organisms.