The Glycosidic Bond (Cambridge (CIE) AS Biology): Revision Note

To make monosaccharides more suitable for transport and storage, and to have less influence on a cell’s osmolarity, they are bonded together to form disaccharides and polysaccharides

Disaccharides and polysaccharides are formed when two hydroxyl (-OH) groups (on different saccharides) interact to form a strong covalent bond called the glycosidic bond (the oxygen link that holds the two molecules together)

Every glycosidic bond results in one water molecule being removed, thus glycosidic bonds are formed by condensation

Each glycosidic bond is catalysed by enzymes specific to which OH groups are interacting

As there are many different monosaccharides, this results in different types of glycosidic bonds forming (e.g maltose has a α-1,4 glycosidic bond and sucrose has a α-1,2 glycosidic bond)

The glycosidic bond is broken when water is added in a hydrolysis (meaning ‘hydro’ - with water and ‘lyse’ - to break) reaction

Disaccharides and polysaccharides are broken down in hydrolysis reactions

Hydrolytic reactions are catalysed by enzymes, these are different to those present in condensation reactions

Examples of hydrolytic reactions include:

• The digestion of food in the stomach and intestines

• The breakdown of stored carbohydrates in muscle and liver cells for use in cellular respiration

Sucrose is a non-reducing sugar which gives a negative result in a Benedict’s test

• When sucrose is heated with hydrochloric acid this provides the water that hydrolyses the glycosidic bond resulting in two monosaccharides that will produce a positive Benedict's test