Carbohydrates

• Carbon, Hydrogen and Oxygen
  • i.e. glycogen, cellulose and starch

Glucose - C₆H₁₂O₆ 

• Hexose
• It takes a ring or cyclic form
• The glucose ring conains 5 carbon atoms and an oxygen atom and is called a pyranose ring

It can exist in two forms:

Fructose

• Hexose sugar
• Fructose forms into a ring with 4 carbon atoms and an oxygen atom called a furanose ring
• Is used in the food industry to manufacture sweets and confectionary

Five crabon sugars, pentoses, are important components of nucleic acids

• e.g ribose

Carbohydrates made of two monosaccharides 

• Sucrose - formed when a molecule of alpha- glucose combines with a molecule of fructose

A reaction in which a molecule of water is removed when two molecules combine is called a condenstation reaction. When monosaccharides combine in this way a Glycosidic bond is formed. In reverse, disaccharides can be digested into monosaccharides by a hydroylsis reaction.

• Maltose - formed by joinig an alpha-glucose molecule to a glucose molecule

 Maltose is a reducing sugar

Built from many monosaccharides linked by glycosidc bonds. 

• A chemist calls this a polymer because it is constructed from a huge number of identical monomers

Some polysaccharides may function as stores of energy e.g glycogen and starch, and others have a structural roles e.g chitin and cellulose

Starch - major storage carbohydrate of most plants

• A mixture of two polysaccharides, both of which are polymers of alpha glucose
• Most starch consist of amylose and amylopectin
  • Amylase
    • Unbranched chain with 1,4 links only
  • Amylopectin
    • Highly branched with many terminal ends. 1,4 and 1,6 links
• The bonds create a helix
• Molecules are both compact and insoluble, but are readily hydrolysed to form sugar due to many terminal glucose molecules

Glycogen - Only found in animals

• Polymer of alpha glucose
• Similar to Amylopectin except glycogen molecule is more highly branched
• Granules of glycogen can be seen in liver cells and muscle fibres using electron microscopy

Cellulose - In plant cell walls

• 1,4 links between beta glucose molecules
• Straight and unbranched
• Every other beta molecule is rotated 180^o  
• Many hydrogen bonds - strong, insoluble, durable and slighty elastic
• Laid down in layers running in different directions, adding strength 
• Most abundant carbohydrate