Disaccharides are a type of carbohydrate, commonly known as “double sugars,” that play various roles in living organisms. They consist of two smaller sugar units chemically linked together.
Understanding Monosaccharides
Monosaccharides are the most basic form of carbohydrates, often referred to as simple sugars. These individual sugar units serve as the fundamental building blocks for more complex carbohydrates like disaccharides and polysaccharides. Common examples of monosaccharides include glucose, fructose, and galactose. Glucose is a primary energy source for cells, while fructose is naturally found in fruits and honey, and galactose is a component of milk sugar.
The Chemical Reaction: Dehydration Synthesis
The formation of a disaccharide from two monosaccharides occurs through a chemical process called dehydration synthesis, also known as a condensation reaction. During this reaction, a molecule of water (H₂O) is removed as the two monosaccharide units join, specifically when a hydroxyl (-OH) group from one and a hydrogen atom (H) from the other are released. This removal of water allows for the creation of a new chemical bond between the two sugar molecules. The specific covalent bond formed between the two monosaccharides during dehydration synthesis is called a glycosidic bond. This linkage connects the two sugar units, transforming them into a single disaccharide molecule.
Examples of Disaccharide Formation
Common disaccharides illustrate this process, formed from specific combinations of monosaccharides. Sucrose, or table sugar, is a disaccharide created when one molecule of glucose bonds with one molecule of fructose. This combination occurs naturally in plants like sugarcane and sugar beets. Another familiar disaccharide is lactose, or milk sugar, which is found in dairy products. Lactose forms when a molecule of glucose joins with a molecule of galactose. The synthesis of lactose primarily occurs in mammary tissue. Maltose, or malt sugar, is a disaccharide composed of two glucose molecules linked together. This sugar is frequently produced during the breakdown of starches, such as in germinating grains like barley, which is why it is present in malted products. In each of these examples, the formation of the disaccharide involves the removal of a water molecule and the creation of a glycosidic bond between the two constituent monosaccharides.