biological molecules

• carbohydrates, proteins and lipids are biological molecules
• biological molecules are found in living organisms and are produced by cells
• Carbohydrates come in different sizes, with the smallest carbohydrates being simple sugars, such as glucose and fructose. We call these simple sugars 'monomers'. Carbohydrate monomers can join together to form carbohydrate polymers, such as glycogen and starch.
• carbohydrate

  diagram

  
• in a complex carbohydrate, there are chemical bonds between the monomers. If these chemical bonds are broken, the complex carbohydrate can be broken down into simple carbohydrates (e.g. starch can be broken down into glucose molecules).

  
• break down of complex carbohydrates into simple carbohydrates (simple sugars) is carried out by enzymes in the mouth and small intestine.
• proteins are made up of long chains of amino acids bonded together. A protein is a polymer, whilst the amino acids it is made from are the monomers.

  
• Enzymes in the stomach and small intestine break proteins down into amino acids.

  
• Lipids contain a single glycerol molecule attached to three fatty acid molecules.

  These fatty acid molecules are often different lengths, and it's the length and structure of the fatty acid molecules that determines whether a lipid is a fat or an oil.

  
•  lipids are not polymers, because they aren't formed from long chains of monomers. This is a key difference between lipids (not polymers), and carbohydrates and proteins (are polymers).
• Enzymes in the small intestine are responsible for breaking lipids down inside the body.
• monomer

  the basic building blocks of larger organic molecules called polymers
• polymer

  large molecules made of small, repeating molecular building blocks called monomers.