The rate at which substrate molecules can be bind to the enzyme's active site, be formed in to products leave can be very rapid. Temperature has complex effect on enzyme activity; a rise in temperature will increase the kinetic energy of the enzyme and the substrate molecules, and therefore will tend to increase the rate of chemical reaction. However, increase the temperature will also affect the stability of the enzymes molecule. Beyond this, a high temperature high internal vibration courses the internal hydrogen bonds to break, unraveling the 3D structure denaturing the enzyme. The substrate can no longer recognise its active site. This is shown in the lock and key theory below
Enzymes only work on one specific type of substrate that means that there is only one kind of substrate that will fit into the enzyme's active site. Most enzymes optimum working temperature is 37°C (body temperature. Enzymes have their optimum temperature which is when the molecules of the enzyme are moving at their fastest. This makes it more likely that the enzyme molecules will collide with the substrate and react. At 60°C, enzymes become completely denatured, which means the molecular bonds of the enzyme are broken, the active site (the area on the enzyme where the reaction takes place) is deformed and the enzyme becomes useless. The molecular bonds of enzymes are generally weak and are broken by slight changes in its surroundings, like temperature or pH. Also there is other ways, which can increase the rate of reaction, which is surface area, enzyme concentration, and substrate of concentration.
Apparatus
2 Beakers
2 Measuring cylinders
Test tube
Delivery tube
Thermometer
Stop clock
Goggles
Hydrogen Peroxide (2cm³ for each test)
Potato
Knife
Cutting Board
Kettle
Plan:
I will collect all the necessary equipment needed. I will then chop up and measure the potato pieces weighing to 3 cm each. For every sample of potato, I test; I will set up the equipment as shown in the diagram. Before starting the experiment, I will ensure the heated water is at the right temperature and check the volume of water in the test tube so that I ensure that the results are fair and reliable. Then I will start by adding 5cm³ of Hydrogen Peroxide into a test tube. I will then cut a piece of potato with a cork borer, using size 4. The next step would be to boil the kettle so we can then add cold water to decrease the temperature down to what is needed for the experiment. Use a thermometer to measure the temperature. When the temperature is correct I will place the test tube into the beaker filled with the heated water. I then will add the potato and the hydrogen peroxide in the test tube. I will quickly then close the bung onto the test tube and place in position. Start the stop clock and time the experiment for 2 minutes. After the 1st and 2nd minute is complete measure the volume of oxygen gas collected. For clarification that oxygen gas is produced perform the oxygen test. I then will repeat the experiment twice.
Safety
Hydrogen peroxide is corrosive and irritant so, to ensure this experiment is carried out safely, I plan to wear goggles to protect my eyes from the hydrogen peroxide. Care also needs to be taken to prevent hydrogen peroxide getting on clothing. I will also take care when preparing the potato pieces with the knife and I will take care with the boiling water to make sure I don’t burn myself.
Variables that Affect the Rate of Reaction
Concentration
Increasing the concentration of an enzyme will increase the rate of reaction as there are more active sites available and so more substrate molecules will be converted quicker. If there is more substrate concentration and the same amount of enzyme concentration the reaction would be slower as the active site would have to convert more substrate molecules and so the time would increase.
Temperature
As temperature increases, molecules move faster as they are given more energy. In an enzyme catalysed reaction this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed. . However, an above certain temperature the structure of the enzymes molecules vibrates so energetically that some of the bonds holding the enzymes molecules in its precise shape begin to break. The enzymes will begin to lose its shape and activity and will become denatured.
PH
Any change in pH affects the reaction and bonding in an enzyme and so alters it shape. Each enzyme has an optimum pH at which its active site best fits the substrate. Changing the pH results in denaturing of the enzyme and a slower rate of reaction.
Inhibition
Inhibitors compete with the substrate for the active sites of the enzyme (competitive inhibitors) or attach themselves to the enzyme, altering the shape of the active site so that the substrate is unable to occupy it and the enzyme cannot function (non-competitive inhibitors). Inhibitors therefore slow the rate of reaction.
Catalysts
A catalyst is a substance that alters the rate of a chemical reaction without being used up. The mass of the catalyst remains unchanged throughout the reaction. The catalyst allows a surface for the particles to stick on which increases the amount of colliding particles, which speeds the reaction up.
(Information used from )
Fair test
In this experiment I will keep the concentrate and the ph constant, and I'll only change the temperature. All the variables I will keep the same except the temperature to make the test fair. I will also keep the surface area the same by drilling a hole with equal diameter through the potato and only use the inside so that it is a controlled experiment. I must also assume that the substrate concentration is the same within the same potato but I cannot be sure and so I must take this into consideration when looking into the reliability of my results. I will do the experiment 2-3 times so that I can get an averaged result and more reliable set of data. I will obtain my set of data by timing the breakdown of the substrate until it is broken down all the way till the outside. I will also have to peel the outside layer of the potato, as it is not digestible and so will alter the results and time it takes to react. To heat the enzyme instead of using a Bunsen burner, which is harder to control, I am going to use cold and boiling water to get rite temperature by mixing the cold and hot together. The temperatures I am taking are at 0 oC, 10 oC, 20 oC, 37.5 oC, 50 oC, 60 oC, and 70 oC. I have increased it in a systematic way so that I can get a large set of data and draw an accurate graph from these results.
