Enzymes 30th September 2020 Learning objectives • Define the term enzyme. • Explain how enzymes work. Big Picture • Many reactions take place within our cells. • These reactions are controlled by enzymes. • Enzymes are proteins that act as biological catalysts. • A catalyst is a substance that speeds up the rate of a chemical reaction. • Enzymes are chemicals that speed up a reaction but are not changed by the reaction. • Most enzymes in human cells work best at a temperature of 37°C, because this is our normal body temperature. Enzymes are proteins • Enzymes are proteins, and can be composed of hundreds of amino acids. • For example, human salivary amylase contains 496 amino acids. • http://biology.kenyon.edu/BMB/jsmol2015/3BLKAmylase/index4.htm l Building up a starch molecule Student’s activity Research on how enzymes work. Create a poster or a powerpoint to explain how enzymes work. Enzyme action 7th October 2020 • L.O Explain how enzyme works. • Plan an investigation on the effect of temperature on enzyme activity. Keywords • Enzyme- A biological catalyst. • Complementary- each piece fits into each other like a key and a padlock or a jigsaw. • Substrate- The substance the enzyme works upon such as a glucose or maltose. Enzyme action • An example of an enzyme-controlled reaction is the joining up of two glucose molecules to make a larger molecule called maltose. • You can see that the enzyme and substrate molecules have complementary shapes (like adjacent pieces of a jigsaw) so they fit together. Other substrate molecules would not fit into this enzyme as they would have the ‘wrong’ shape. Can this enzyme act on the food substance? Molecule of a substance Other substrate molecules would not fit into this enzyme as they would have the ‘wrong’ shape. Can this enzyme act on the food substance? A molecule of the substance Building up ‘reaction’ involving an enzyme and a substrate The product (substance AB) is released by the enzyme molecule and the enzyme is then free to repeat the reaction with more substrate molecules. Breaking up reaction involving an enzyme and a substrate. Enzyme action • Molecules of the two substances might have combined without the enzyme being present, but they would have done so very slowly (it could take hours or days to happen without the enzyme). • By bringing the substances close together, the enzyme molecule makes the reaction take place much more rapidly. Enzyme action • The process can be extremely fast: it has been found that catalase, a very common enzyme found in most cells, can break down 40 000 molecules of hydrogen peroxide every second! • A complete chemical reaction takes only a few seconds when the right enzyme is present. Students’ activity • Use the worksheet provided to plan an investigation on the effect of temperature on enzyme activity. • Use the planning sheet to: ØWrite down the research question ØIdentify the variables ØMake a hypothesis ØMaterials needed ØMethod used ØSafety precautions Temperature, pH and Enzymes • L.Os • Explain how temperature affects enzyme activity. • Explain the effect of pH on enzyme activity. 14th Oct 2020 Temperature and enzyme activity Temperature At 370C (warm water) At 200C (cold water) At 4OC (ice water) observation The colour of iodine changed from blue-black to colourless. The colour of iodine changed to light blue. The colour of iodine changed to light blue. Explanation The enzyme broke down starch into sugar. There is no starch in the mixture. The enzyme broke down some starch into sugar. The process was very slow. The enzyme broke down some starch into sugar. The process was extremely slow. Temperature and enzymes • Most enzymes in the human body work best at about 37°C, because this is our normal core body temperature. • The temperature at which an enzyme works best is known as the optimum temperature. Describe the shape of this graph? As the temperature increases, the particles gain kinetic Energy and move faster. The particles collide more frequently. The enzyme collides with the substrate more frequently thus Increasing the rate of reaction. Above optimum temperature, the enzyme is denatured and Therefore the rate of reaction decreases. The rate of reaction increases as the temperature increases, reaching a maximum at the optimum temperature for this enzyme (close to 37 °C). This section of the graph follows the same general pattern as many other reactions: the rate of reaction approximately doubles for every 10 °C increase in temperature. If the temperature rises above the optimum for an enzymecatalysed reaction, the rate of reaction decreases very quickly. This is different to the rate/temperature graph for a reaction catalysed by an inorganic compound, which will continue to show an increased rate as temperature increases. • An increase in temperature increases the rate of an enzyme-catalysed reaction because it makes the molecules move more. • This increases the chances of a collision between the active site of the enzymes and the substrate molecules If the temperature rises above an enzyme’s optimum temperature, the shape of the enzyme will start to change. This changes the shape of the active site as well, so the substrate can no longer bind with the enzyme. This will decrease the rate of reaction. When the shape of the enzyme changes, the enzyme is said to have been denatured. pH • Different enzymes work best at different pH values. • For example, salivary amylase, pepsin and trypsin are all digestive enzymes. • Amylase digests starch into maltose. It has an optimum pH of 7. • Pepsin, which digests proteins, has an optimum pH of 2. • Trypsin is an enzyme produced by the pancreas. It also digests proteins, by breaking them into small peptides. It has an optimum pH of 8.5.