Enzymes

• Living things have thousands of different chemical reactions going on inside of them all the time. These reactions need to be carefully controlled - to get the right amounts of substances.
• You can make a reaction quicker by raising its temperature but there's 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. So they usually only catalyse one specific reaction each.
• For an 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.
• Changing the temperature changes the rate of an enzyme-catalysed reaction. Like with any 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 at best.
• PH affects enzymes. If its 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 enzyme.
• All enzymes have an optimum pH that they work best at. It's often neutral pH 7, but not always - e.g. 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.