Forming the Glycosidic Bond

• Monosaccharides


  To make monosaccharindes more suitable for transport, storage and to have less influence on a cell's osmolarity, They are bonded together to form disaccharides and polysaccharides
• Forming the glycosidic bond

  1. Two hydroxyl (-OH) groups (on different saccharides) interact to form a strong covalent bond called the glycosidic bond

  2. Glycosidic bond results in one water molecule being removed, thus glycosidic bonds are formed by Condensation

  
• Glycosidic bond


  The oxygen link that holds the two molecules together
• 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)

  
• Types of Glycosidic Bonds

  • Maltose: α 1,4 (Disaccharide)
  • Sucrose: α 1,2 (Disaccharide)
  • Cellulose: β 1,4 (Polysaccharide)
  • Amylose: α 1,4 (Polysaccharide)
  • Amylopectin: α 1,4 and α 1,6 (Polysaccharide)

  
• Breaking the glycosidic bond

  1. The glycosidic bond is broken when water is added in a hydrolysis reaction

  2. Disaccharides and polysaccharides are broken down in hydrolysis reactions

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

  4. Examples of hydrolytic reactions include the digestion of food in the alimentary tract and the breakdown of stored carbohydrates in muscle and liver cells for use in cellular respiration

  
• Sucrose


  • 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