enzymes

• a catalyst is a substance which increases the speed of a reaction without being changed or used up in the reaction
• 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
• 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
• 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
• the active site changes shape a little as the substrate binds to it to get a tighter fit
• changing the temperature changes the rate of an enzyme-catalysed reaction
• a higher temperature increases the rate at first, but 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 any more. the enzyme is said to be denatured
• all enzymes have an optimum temperature that they work best at
• the pH affects enzymes. if it's too high or too low, the pH interferes with the bonds holding the enzyme together. this changes the shape of the active site and denatures the enzymes
• all enzymes have an optimum pH that they work best at. it's often neutral pH 7, but it can also work best at pH 2, which means it's well suited to the acidic conditions