How are monosaccharides linked to form disaccharides?

Monosaccharides are linked to form disaccharides through a process called dehydration synthesis or condensation reaction.

In more detail, monosaccharides, the simplest form of carbohydrates, can combine to form more complex sugars like disaccharides. This process involves the removal of a water molecule, hence the term 'dehydration synthesis'. It's also known as a condensation reaction because water (H2O) is a by-product of the reaction.

The reaction occurs between two monosaccharides, each contributing one part of the water molecule that will be removed. One monosaccharide donates a hydroxyl group (OH), while the other donates a hydrogen atom (H). When these two components combine, they form a water molecule, which is then released. The remaining parts of the monosaccharides then bond together, forming a disaccharide.

This bond between the two sugar molecules is called a glycosidic bond. It's a type of covalent bond, meaning it involves the sharing of electrons between atoms. The formation of a glycosidic bond is what links the two monosaccharides together to form a disaccharide.

An example of this process can be seen in the formation of sucrose, a common disaccharide. Sucrose is formed by the condensation of a glucose molecule and a fructose molecule. During this reaction, the glucose molecule donates a hydroxyl group, and the fructose molecule donates a hydrogen atom. These combine to form water, which is released, and the remaining parts of the glucose and fructose molecules bond together, forming sucrose.

This process is not limited to the formation of disaccharides. It's also how polysaccharides, or complex carbohydrates, are formed. Polysaccharides are simply long chains of monosaccharides linked together by glycosidic bonds. The same dehydration synthesis process occurs, just multiple times, to link all the monosaccharides together.