• Most of the molecules in living organisms fall into three categories:?carbohydrates, proteins and lipids
• These?all contain carbon?and so are described as organic molecules

Carbohydrates

• Carbohydrates contain the elements carbon, hydrogen and oxygen
• A monosaccharide is a?simple?sugar e.g.?glucose?(C₆H₁₂O₆) or?fructose
  • Glucose molecules contain lots of?energy?which can be released in respiration by?breaking the bonds?between the carbon atoms

   

• A?disaccharide?is made when?two?monosaccharides join together
  • Maltose?is formed from?two glucose?molecules
  • Sucrose?is formed from?one glucose?and?one?fructose?molecule

   

• A?polysaccharide?is formed when?lots?of monosaccharides join together
  • Starch, glycogen or cellulose?are all formed when?lots?of glucose?molecules join together
  • Polysaccharides are insoluble and therefore useful as storage molecules

   

Glycogen, cellulose and starch are all made from glucose molecules

Fats

• Most fats (lipids) in the body are made up of?triglycerides
• Their basic unit is?one glycerol molecule?chemically bonded to?three fatty acid chains
• The fatty acids vary in size and structure
• Lipids are divided into?fats?(solids at room temperature) and?oils?(liquids at room temperature)

The structure of a triglyceride

Proteins

• Proteins are formed from long chains of?amino acids
• There are 20 different amino acids
• When amino acids are joined together a?protein?is formed
• Amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins
  • Examples of proteins include?enzymes,?haemoglobin, ligaments and keratin

   

Amino acids join together to form proteins

Protein shape

• Different proteins have different amino acid sequences resulting in them being?different shapes
• Even a small difference in the?amino acid sequence?will result in a completely?different?protein being formed
• The?different sequences of amino acids?cause the polypeptide chains to?fold in different ways?and this gives rise to the different shapes of proteins
• In this way, every protein has a?unique 3-D shape?that enables it to carry out its function
• The shape of a protein?determines its function
• For example:
  • Enzymes?have a specifically shaped?active site?- this is where a?specific substrate?molecule fits in order for a reaction to take place
  • If the shape of the active site does not match the shape of the molecule that fits into it, the reaction will not take place
  • Antibodies?are proteins produced by certain types of?white blood cells?that attach to antigens on the surface of pathogens
  • The?shape of the antibody?must match the?shape of the antigen?so that it can attach to it and signal it for destruction

   

Every enzyme has a different shaped active site-specific to one substrate