AS AQA Biology: Carbohydrates




Uses include:

1. Providing energy and regulation of blood glucose

2. Sparing the use of proteins for energy

3. Breakdown of fatty acids and preventing ketosis

4. Biological recognition processes

5. Flavour and Sweeteners

6. Dietary fibre

These only contain Carbon, Oxygen and Hydrogen and include monomers, dimers and polymers as shown in the diagram below:


These are the simplest form of sugars and are usually colourless, water-soluble and crystalline.

The general formula is Can H2n On. The most important monosaccharide is glucose which is a hexose sugar, (six carbons) and has the formula C6 H12 O6. It forms a six sided ring as shown below. It has many isomers with the same formula but different structure these include fructose and galactose.

Beta Glucose, an alpha glucose has the OH-H bond the other way round.


These are known as double sugars, and are essential two Monosaccharides joined together via a glycosdic bond, which involves the formation of water. This is called a condensation reaction. The reverse, hydrolysis involves the addition of water to break bonds.

There are three common disaccharides:

Maltose (or malt sugar) is glucose 1-4 glucose. It is formed on digestion of starch by amylase, because this enzyme breaks starch down into two-glucose units. Brewing beer starts with malt, which is a maltose solution made from germinated barley. Maltose is the structure shown above.

Sucrose (or cane sugar) is glucose 1-2 fructose. It is common in plants because it is less


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