Hydrogen Peroxide  Water + Oxygen DO NOW: Both reactions show decomposition reaction of hydrogen peroxide. What is the difference between top reaction and the bottom reaction? Reaction #1 Hydrogen Peroxide  Water + Oxygen Catalase Reaction #2 Hydrogen Peroxide  Water + Oxygen #1 Takes longer to occur than #2 #2 uses catalase An enzyme is used in the #2 and not in #1 #2 has a helper (enzyme) to make the reactant break down.

Effect of Enzyme on Chemical reaction What does an enzyme do to the Reaction?

H2O2  H2O + O2(g) Purpose of the Lab: Compare a enzyme catalyzed reaction to a non-enzyme catalyzed reaction. Observe how changing the source, form and quality of the enzyme influences the reaction. Below is the chemical reaction you observed: H2O2  H2O + O2(g)

Post Lab Questions Does the data table contain qualitative or quantitative data? Which test tubes indicated a chemical reaction was taking place? How did you know? Which test tubes indicated a chemical reaction was not taking place? How did you know? Which test tube is the negative control? What does it lack? Which test tube showed the effect of temperature that influenced enzyme function? Explain. Which test tube attempted to show the effect of increasing enzyme concentration? Explain. Which test tube illustrates the absence of an enzyme? What was the source of catalase in this lab? What was the cause of the bubbles? What would you need to determine if this reaction was exothermic or endothermic? Catalase works best at pH 7. Predict what would happen to the decomposition of hydrogen peroxide was lowered to a pH of 2. Write a hypothesis.

Potato versus Liver How are you sure the potato or liver is causing the decomposition reaction to occur? It is believed that both potato and liver contain catalase. Provide evidence to support this. Can your data support the hypothesis that using liver provides a greater concentration of enzyme? Purpose of Questions #1 & 2 was to emphasize the importance of a control. Purpose of Question #3 is to see how observations can generate new questions to be answered.

What does Bubbles or Bubbling really indicate? Rate – something per time How would you express the rate for The reaction you overserved? # of bubbles formed per minute If you reran the lab, how would obtain this information? Why would someone have bubbling occur in test tube 1 after a while?

An enzyme only lowers the EA How an enzyme Works… Unanalyzed – without enzyme Catalyzed – with enzyme How does adding the enzyme change the graph? Does an enzyme affect the delta G? An enzyme only lowers the EA

How does the enzyme lower EA? Catalase O2 Enzyme weakens or stresses the bond holding the H’s and O’s in H2O2. When bonds reach enough stress, they break and the reaction proceeds making water and oxygen. Without the enzyme, it will take more energy and time to stress the bonds for the reaction to proceed.

Enzyme available with empty active site Active site Substrate 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme (sucrase) Glucose Fructose Figure 5.15 The catalytic cycle of an enzyme. 4 Products are released 3 Substrate is converted to products

Using the diagram on previous slide… Name the type of reaction occurring. Where on the diagram where would the EA start to be lowered? How could you modify the diagram to show a reaction with an unaffected EA? Using the illustrations of enzymes from the previous slide and the one for catalase, could sucrase be used for the decomposition of hydrogen peroxide? Write out the equation for the chemical reaction for the slide.

Progress of the reaction without enzyme EA without enzyme EA with enzyme Reactants Energy Net change in energy (the same) Reaction with enzyme Figure 5.14 The effect of an enzyme is to lower EA. Products Progress of the reaction

5.15 A specific enzyme catalyzes each cellular reaction For optimum activity, enzymes require certain environmental conditions Temperature is very important, and optimally, human enzymes function best at 37ºC, or body temperature while certain prokaryotes (bacteria) can live in extreme temperature because their enzymes do not denature at temperature above 100 degrees Celsius. Temperature above optimal will cause enzymes to denature and no longer function. Temperature below optimal will slow molecular motion decreasing the likelihood of forming an enzyme-substrate complex to catalyze a reaction. A good number of enzymes require a pH around neutrality for best results Salinity (concentration of salt in solution) can affect enzyme function. Certain chemicals also alter enzyme function and have been used to kill bacteria. For the BLAST Animation Enzymes: Types and Specificity, go to Animation and Video Files. Student Misconceptions and Concerns 1. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. 2. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. Copyright © 2009 Pearson Education, Inc.