Biology coursework: Substrate specificity in yeast AIM: To find out which substrate (glucose, starch, maltose, sucrose or lactose), does yeast, the organism containing the enzyme, breaks down the quickest. Introduction: Usually, every enzyme has a specific substrate that is what we call the “lock and key” theory. We can try the reaction of an enzyme with different substrates and this enzyme will just work well with one of those substrates. One type of reaction catalyzed by enzymes is anaerobic respiration. (fermentation), made by yeast that uses a sugar as a substrate. This reaction will produce CO2 and energy.
Measuring how much CO2 the reaction produces we could know how well the enzyme is working with a substrate, checking thus its specificity. Materials: 5 Ignition tubes Pipette Glucose Maltose Sucrose Lactose Yeast Cotton wool Test tubes Stop watch Ruler Variables: Independent variable: substrate (glucose, starch, maltose, lactose, sucrose), enzyme (yeast), volume of substrate, volume of enzyme. Dependent: volume of CO2 released (measured in mm) Controlled variables: Temperature, pressure, time.
Method: 1- Fill 5 ignition tubes, half with yeast (2.0 ml) and half with each corresponding substrate (2.0 ml), using a pipette. 2- Quickly after the mixture is done, place the ignition tubes upside down in a test tube, helping yourself with a pen. 3- Start the stop watch once the ignition tube is upside down in the test tube, and measure the space left (this will be time 0) 4- Place some cotton wool on the top of each test tube in order to block oxygen, and therefore, for anaerobic respiration to occur.
5- Prepare one mixture with the yeast (enzyme), and with water, to act as a control. Treat the control in the same way you have done it with the samples. 6- As anaerobic respiration occurs, CO2 is released displacing the mixture of yeast and substrate into the test tube. Measure the amount of CO2 released during 20 minutes, taking a reading of the empty space inside the ignition tube every 5 minutes. 7- Repeat the experiment 3 times for statistical purposes.