Enzymes

• Enzymes are catalysts produced by living things
• Living things have thousands of different chemical reactions going on inside them all the time. These reactions need to be carefully controlled - to get the right amounts of substances
• You can usually make a reaction happen more quickly by raising the temperature. This would speed up the useful reactions but also the unwanted ones too.
• There is a limit to how far you can raise the temperature inside a living creature before its cells start getting damaged
• Living things produce enzymes that act as biological catalysts
• Enzymes reduce the need for high temperatures and we only have enzymes to speed up the useful chemical reactions in the body
• A catalyst is a substance which increases the speed of a reaction, without being changed or used up in the reaction
• Enzymes are all large proteins and all proteins are made up of chains of amino acids. These chains are folded into unique shapes, which enzymes need to do their jobs

  
• Chemical reactions usually involve things either being split apart or joined together
• Every enzyme has an active site with a unique shape that fits onto the substance involved in a reaction

  A) Active site

  
• Enzymes are really picky - they usually only catalyse one specific reaction
• For the enzyme to work, the substrate has to fit into its active site

  
• If the substrate doesn't match the enzyme's active site, then the reaction won't be catalysed

  
• This diagram shows the 'lock and key' model of enzyme action. This is simpler than how enzymes actually work

  
• In reality, the active site changes shape a little as the substrate binds to it to get a tighter fit. This is called the 'induced fit' model of enzyme action
• The substance that an enzyme acts on is called the substrate
• Enzymes need the right temperature and pH
• Changing the temperature changes the rate of an enzyme-catalysed reaction
• Like with any reaction, a higher temperature increases the rate at first
• If it gets too hot, some of the bonds holding the enzyme together break. This changes the shape of the enzyme's active site, so the substrate won't fit anymore
• If an enzyme gets too hot, it is said that it is denatured
• All enzymes have an optimum temperature that they work best at
• The pH also affects enzymes. If it gets too high or too low, the pH interferes with the bonds holding the enzyme together and denatures it
• All enzymes have an optimum pH that they work best at. It is often neutral pH 7, but not always
• Pepsin is an enzyme used to break down proteins in the stomach. It works best at pH 2, which means it's well-suited to the acidic conditions there