Classwork #10 - Enzymes Key Vocabulary protein enzyme catalyst reactant substrate active site product

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1 Biology Noble efforts change lives. Name: Excellence. Tenacity. Community. Reflection. Classwork #10 - Enzymes Key Vocabulary protein enzyme catalyst reactant substrate active site product Pre-Reading The biomolecules produced by cells perform many functions that sustain life. Biomolecules such as carbohydrates and fats store an abundance of energy that the cell can use and metabolize. DNA, another type of biomolecular polymer, contains all the information and instructions that a cell follows. Proteins are the most varied of the common cellular biomolecules. The diversity of proteins within a cell reflect that variety of functions that they perform. Proteins can be used to provide structure to a cell, repair damage, or break down large molecules, among many other functions. Enzymes are one type of protein polymer that play a unique role in the cell. Enzymes are large biomolecules that are responsible for facilitating the thousands of chemical reactions that sustain life. More specifically, they are catalysts they help speed up the rate of these chemical reactions in living organisms. Without enzymes, breaking down polymers into their component monomers (or vice versa, building polymers out of their monomers) would take too long and lead to the demise of the organism. Organelles within cells contain enzymes that help them carry out their specific functions. For example, lysosomes, a type of organelle, contain enzymes that help the cell digest food and other foreign molecules. Due to the multitude of chemical reactions that occur in a cell, enzymes are very specific, usually recognizing just one or a few closely related set of reactants in a chemical reaction. For this reason, each different enzyme in the cell is responsible for speeding up only a single type of chemical reaction. In a chemical reaction that is helped by an enzyme, the reactants are called the substrates. Substrate binds with enzymes at the enzyme s active site. The active site is the location on the enzyme where the substrate and enzyme make contact. The enzyme then helps to convert the substrate into products of the specific chemical reaction. The chemical reaction is considered complete once there are no substrates left to be converted into products. Figure 1 below displays the interactions of an enzyme, substrate, and products. A C B D Figure 1 Figure 1

2 A cell s physical and chemical environment affects enzyme activity. The activity of an enzyme is affected by general environmental conditions, such as temperature and ph. Each enzyme works best at certain optimal conditions, which keeps the enzyme and active site in its properly folded structure. When conditions are suboptimal, the bonds that hold the enzyme together begin to destabilize, and the protein begins to unfold out of its proper configuration. This loss of structure is called denaturation. Experiment 1 In the lab, scientists were able to speed up the decomposition of 25mL of hydrogen peroxide (H2O2) with the use of 10 ml of catalase, an enzyme. The decomposition of hydrogen peroxide is shown in the chemical reaction below. Table 1 and 2 show the progression of the reaction in the presence of catalase and the absence of catalase. 2H 2O 2 2H 2O + 2O 2 Table 1 Table 2 Time Volume (ml) Time Volume (ml) (min) H2O2 H2O Catalase (min) H2O2 H2O Catalase Experiment 2 Knowing that enzymes serve to facilitate the change of substrate to product, a student wanted to see the effects of an enzyme on the rate of a biochemical reaction. The student studied the decomposition of lactose into its component monomers of glucose and galactose. Lactose is a polymerized sugar that gives milk its sweetness. When broken down, its glucose and galactose (a sugar monomer similar to glucose) can be used for cell respiration. The decomposition reaction for lactose is shown below: Lactose à Glucose + Galactose In Part A of the experiment, the student collected 10.0 ml of lactose and mixed it with 2.0 ml of, a protein produced in the small intestine that catalyzes the decomposition of lactose. The student measured the amount of galactose monomers produced until the reaction stopped and graphed this data with respect to time. The student repeated this experiment using 1.0 ml of (Part B), 0.5 ml of (Part C) and finally no. The results of the experiment are shown in Figure 2 below. Amount of D Key: A: 2.0 ml of B: 1.0 ml of C: 0.5 ml of D: 0.0 ml of Figure 2

3 Questions 1. Based on the information in the passage and your knowledge from Lesson 1.7, explain what molecule is the monomer of enzymes. 2. Consider the relationships of the structures shown in Figure 1. a. The enzyme shown in Figure 1 is labeled at four different parts at A, B, C, and D. Explain which label indicates the active site of the enzyme. b. The arrows in Figure 1 are labeled 1, 2, and 3. Describe the interactions between the enzyme, substrate, and products that are occurring at each of the labeled steps. c. Due to a mutation in the cell, the shape of the enzyme shown in Figure 2 is altered into the one shown to the right. Predict how this mutation would affect the enzyme s function and interaction with the given products and reactants.

4 3. Answer the following questions regarding Experiment 1: a. Using Tables 1 and 2 explain the role of enzymes in chemical reactions. b. Compare the average rate of reaction over 2 minutes for an enzyme-catalyzed reaction to that of a reaction without any enzyme. c. A student suggests that rather than measuring the volumes of hydrogen peroxide or water, another way to determine the rate of reaction would be to measure the amount of oxygen produced. Determine whether or not this new method is an experimentally viable method and why. 4. Based on the following graph and the information in the passage, explain the changes in observed enzyme activity as temperature increases. Figure 3

5 5. Answer the following questions regarding the design of Experiment 2: a. Identify the substrate(s), product(s), and enzyme(s) in this experiment. b. Describe the purpose of conducting Experiment According to Figure 2, for each trial in the experiment (A, B, C, and D), the amount of galactose increased as time passed. Explain why this trend exists. 7. Analyze the data only for Trial A of the experiment in Figure 2. a. Compare the rate of reaction in the first half of the experiment to that of the second half. b. Explain why this trend exists. 8. Consider the point in time in Figure 2 marked by the arrow. a. What trend do you see when comparing the data points for each of the different trials at this point in time?

6 b. Explain why this trend exists.