Debbie Spicer
The role of proteins
Proteins are made up of amino acids which are joined together to form one or more polypeptide chains these chains are folded into a three-dimensional shape which is different from protein to protein. The shape is determined by the order that the amino acids are arranged in this is the primary structure of the protein. The secondary structure of the protein is held together by hydrogen bonds. The polypeptide chains may coil to form a α helix or they may lie in a β-plated sheet. The chain may be folded again to give its tertiary structure. Some proteins are made up of more than one polypeptide chain and the way in which these chains are held together determines its quaternary structure. Haemoglobin is made out of four polypeptide chains so it has a quaternary structure. Each of the polypeptide chains in haemoglobin is attached to a haem group, which is important in the transport of oxygen around the body.
The structure of a protein is very important in enzymes as the tertiary structure of an enzyme gives it its active site. The active site is where the substrate binds to in a reaction. If the active site were a different shape, the substrate would not fit in it so the enzyme would not catalyse the reaction. The enzyme reduces the amount of activation energy that is needed for a reaction to take place so that rate of reaction increases. It also means that a reaction can occur at a lower temperature and pressure. According to the induced fit theory when a substrate combines with an enzyme, it induces it to change its shape so that the amino acids in the active site can carry out their catalytic function effectively. Once the reaction has occurred. Products are formed that are of different shapes to the original substrate so they no longer bind to the active site and diffuse away. The enzyme returns to its original shape so that it can be used again.
