Enzymes

• enzymes are catalysts produced by living things
• living things have thousands of different chemical reactions going on inside them all the time
• these chemical reactions need to be carefully controlled to get the right amounts of substances
• you can usually make a reaction happen quicker by increasing the temperature but this would speed up all reactions- even unwanted ones
• enzymes reduce the need for high temperatures and we only have enzymes to speed up 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
• chemical reactions usually involve things being split apart or joined together
• the substrate is the molecule being changed in the reaction
• every enzyme has an active site- the part where it joins on to its substrate to catalyse the reaction
• enzymes only work with one substrate. they are said to have a high specificity for their substrate
• for the enzymes to work, the substrate has to fit into the active site. this is called the lock and key mechanism
• changing the temperature changes the rate of an enzyme-catalysed reaction
• like with any reaction, a high temp increases the rate at first
• if it gets too hot, the bonds holding the enzyme together break. this means the enzyme is denatured
• all enzymes have an optimum temp that they work best at
• the pH also affects enzymes. if it's too high or low, the pH interferes with the bonds holding the enzyme together
• the pH can change the shape of the active site and denature the enzyme
• all enzymes have an optimum pH they work best at. it's usually pH 7 but not always (pepsin is an enzyme that works best at pH 2)
• substrate concentration also affects the rate of reaction. the higher the substrate concentration, the faster the reaction. this is because the enzyme is more likely to meet up and react with a substrate
• this is only up to a point as after that, all the active sites are full and adding more substrates makes no difference
• to calculate the rate of reaction use:

  rate = 1000 / time
• proteins, lipids and some carbohydrates are big molecules
• it's important that organisms are able to break down bigger molecules into their smaller components
• digestive enzymes break down the big molecules into smaller, soluble molecules. these can pass easily through the walls of the digestive system, allowing them to be absorbed into the bloodstream
• the bloodstream passes smaller molecules into the cells
• plants store energy in the form of starch (a carbohydrate). when plants need energy, enzymes break down the starch into smaller molecules called sugars. these sugars can then be respired
• enzymes called carbohydrases convert carbohydrates into simple sugars. amylase converts starch into maltose and other sugars
• protease converts proteins into amino acids
• lipase converts lipids into glycerol and fatty acids
• organisms need to be able to synthesise carbohydrates, proteins and lipids from their smaller components. enzymes are used to do this
• carbohydrates can be synthesised by joining together simple sugars
• glycogen synthase is an enzyme that joins together lots of chains of glucose molecules to make glycogen