Title: Enzyme Catalysis of Hydrogen Peroxide by Catalase
Problem and Objectives: How do different temperatures and different levels of pH affect the reaction rate of the enzymes in chicken liver? Demonstrate the activity of an enzyme in living tissue, observe the effects of changes in temperature and pH on the activity of an enzyme, perform analyses for the presence of an enzyme in tissues, and analyzing relationships between environmental conditions and enzyme activity. Background: Cells produce proteins which are called enzymes and their job is to help reduce the amount of energy needed to start a reaction. Enzymes are catalysts which are chemical substances that reduce the amount of activation energy needed for the reaction to begin. All enzymes are all proteins or RNA molecules that speed up metabolic reactions and help to break down poisonous chemicals in the organism’s body. An enzyme will only react if the enzyme fits well with the substrate, which is why they are similar to a lock and key. The substrate will bind to the enzyme at the active site and when this happens a slight change in the shape of the enzyme will occur. This change of shape binds the enzyme to shape of the substrate and then weakens the chemical bonds of the substrate. When this happens it produces the activation energy that is needed for a chemical reaction to take place. The enzyme will only bind correctly with the substrate if the environmental conditions are to their liking. They like to work at room temperature and at the neutral range of pH. After the reaction the enzymes are not destroyed or changed and can be reused. Activation energy is what is needed for many chemical reactions to take place and for most reactions the amount of activation energy is very high. (Crafton 2012) and (Postlethwait and Hopson 2009) Hypothesis (es): If extreme changes in temperature affect the enzyme, then lowering or raising the temperature by amounts far out of normal range will cause the enzyme to function incorrectly. If extreme changes to the pH level affect the enzyme, then lowering or raising the acidity or alkalinity by drastic amounts will cause the enzyme to not work correctly. Procedures: Get safety goggles and put them on. For the normal catalase activity first put some hydrogen peroxide into a clean test tube, and then use tweezers to put a small piece of chicken liver in the test tube. Then push the liver down into the hydrogen peroxide using a stirring rod, and watch the bubbles of oxygen being released. This heated up the test tube which was another clue that this reaction was an exergonic reaction. After observing this then get another clean test tube and hydrogen peroxide in it and add a small piece of liver and watch the reaction occur in this one too and give off a lot of oxygen bubbles as well. After this, pour the liquid into yet another clean test tube and think about what would happen if more liver was placed in this liquid. Place the liver into the liquid mixture of hydrogen peroxide and liver and the new mixture didn’t fizz as much as with just the hydrogen peroxide and one thing of liver. The thought of what would happen when adding more liver to the mixture was correct because it was thought that the mixture would cause a smaller reaction and it did. If more hydrogen peroxide was then added to the liver from the previous steps then there would be a more gas releasing reaction than adding more liver. Test this and it was true that more hydrogen peroxide would cause a larger reaction. This proves that enzymes, such as chicken liver are reusable, while the substrates, such as hydrogen peroxide, are not.
Next get four clean test tubes and put equal amounts of hydrogen peroxide in each and put a small piece of liver in one, a small piece of potato in another, the third a small piece of apple, and to the last one a small piece of carrot. After putting these in their respective test tubes, record the reaction rate of each substance in...
References: Crafton-Sizemore, L. 2012. Notes on Biochemistry 4 September 2012
Catalase Handout 2012. 4 September 2012
The website http://www.mrothery.co.uk/enzymes/enzymes.htm was very helpful for this lab also.
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