Practice tests for lab quiz.pdf

all living things are able to transform energy from one form to another. Enzymes are biological catalysts that can increase the rate of a chemical reaction (e.g. the breakdown of sugar to energy) by more than a million-fold. Almost all enzymes are proteins, composed of subunits called amino acids....

all living things are able to transform energy from one form to another. Enzymes are biological catalysts that can increase the rate of a chemical reaction (e.g. the breakdown of sugar to energy) by more than a million-fold. Almost all enzymes are proteins, composed of subunits called amino acids. 20 different amino acids that become the building blocks of proteins. It is the number of amino acids (hundreds to thousands) and their specific sequence that is unique for each protein or enzyme and will determine if and how the protein works. Changes in the sequence of the amino acids can sometimes have serious or even deadly consequences (e.g. sickle cell anemia is the result of a change in only one amino acid in the beta chain of a hemoglobin molecule). Enzymes are highly specific in the reaction they catalyze; usually, a particular enzyme mediates only one chemical reaction. Enzyme-mediated reactions begin with one or more reactants called substrates. Again, only this substrate will react with a given enzyme. In the presence of the enzyme, the substrate binds to the enzyme and is converted into product(s). While the substrate is converted into a new chemical (product), the enzyme itself remains unchanged by this chemical reaction and thus can be recycled to react with more substrate and produce more product. For an enzyme to work, it must first chemically bind to the substrate. This occurs at a specific region called the active site. A number of generalizations can be made concerning the active site: It occupies a relatively small portion of the enzyme molecule. It forms a three-dimensional cleft or crevice in the enzyme molecule. The specificity of the binding depends on the precisely defined arrangement of the amino acids in the active site. Substrates are usually bound to the active site by relatively weak chemical forces. The physical interaction between the enzyme and substrate is called an “induced fit” - The enzyme physically changes shape to interact with the substrate in the active site– bending and breaking (or forming) chemical bonds to produce the product. In addition to substrates, other molecules exist that can interfere with the bonding of the enzyme and substrate. These substances are called inhibitors because they prevent the reaction from occurring. Inhibitors primarily work in either of two ways; (1) they can bind to the active site, thereby blocking it, or (2) they can cause a conformational change in the enzyme so that it can no longer bind with the specific substrate. The importance of enzymes goes beyond transforming the food we eat into energy. In fact, enzymes are responsible for a myriad of functions and can touch our lives in many ways. Therefore they include samples called “controls.” A control is a sample that will give a result of known or predictable outcome (either positive or negative). A positive control will show you the result you expect if the reactants (enzyme, substrate, buffer, etc.) are working correctly. This may be verified by a color change in the solution, evolution of gas bubbles, formation of a precipitate, etc. A negative control is one where one of the key reactants (e.g. enzyme or substrate) is deliberately left out of the mixture. It is used to confirm that there are no contaminants in the materials being used. Hence, the expected reaction does not occur within a negative control sample. Even at a temperature of 0C, one molecule of catalase can decompose about 5,000,000 molecules of hydrogen peroxide in one minute! The purpose of this lab is to explore the effects of various parameters (e.g. concentration, pH, and temperature) on the activity of the enzyme catalase. Your data collection will involve monitoring the production of oxygen (bubbles/foam) from the break down of the hydrogen peroxide. The amount of oxygen generated from the reaction is directly proportional to the “activity” of the enzyme. Later, your lab instructor will prepare an extract from fresh potatoes. This extract contains catalase and will be used in the remaining portions of the lab exercise. Depending on the conditions specified (e.g. enzyme concentration, temperature, pH, etc.), the enzyme activity can vary considerably. Optimal conditions are those that generate the greatest amount of oxygen (i.e. production of foam). Part C. Effect of Temperature on Enzyme Activity 1. Describe what happens to the activity of catalase as temperature increases. As the temperature increases there was less activity except for 37℃ where there was the most enzyme activity 2. At what temperature does catalase (from potatoes) have its optimal activity? 37℃ 3.What effect does boiling have on enzyme activity? Why? The effect that boiling caused the enzyme activity to be less because it denatures Part D. Effect of pH on Enzyme Activity 1. Based on your results, what is the optimal pH for catalase in potatoes? pH: 8&10 2. Is the pH of the potato extract at the optimal pH for this enzyme? Why or why not? The Ph 8 and 10 of potato extract were optimal for this enzyme because it caused more enzyme activity. 3. Based on the criteria you just studied (i.e. concentration, temperature, and pH), summarize the optimal conditions for catalase from potatoes. 37℃, Ph 8&10,Concentration from tube 4 were the optimal for catalase for the potato because they gave the best enzyme activity 4. Suppose you were given a papaya extract to test for catalase. Describe how you would go about investigating and determining the optimal conditions for catalase. I would use the Enzyme concentration experiment and do the 4 tubes, 0.5, 1, 2, 4 ml of papaya extract and distilled water and hydrogen peroxide,then test the amount of foam which the enzyme activates. QUESTIONS:All work is to be your own; answer all questions in complete sentences. Part A. Presence of catalase in potatoes: 1. What differences in enzyme activity did you notice among the four tubes? Explain why. Tube #1: there was no enzyme activity because there was no enzyme source to initiate the reaction. Tube #2: There was no enzyme reaction because there was not enough surface area for binding for there to be a reaction because it was a whole potato Tube #3:There was an enzyme reaction because the mashed potato has more surface area for binding causing a reaction to happen Tube #4:This was the best enzyme reaction because the enzyme was catalyzed which gave a better reaction 2.Why did we use Tube #1 as a "Control?" we used tube #1 as a control to be able to have a baseline for the variables we changed 3. Was Tube #1 a positive control or negative control? Explain. tube #1 is a negative control because it was a baseline to show how the experiment worked when adding in the variables. 4. Which other tube served as a "control" for this experiment? Was it a positive or negative control? Explain. tube #2 was used as a control. The control was negative because even though there was no reaction for tube 2 there were reactions for tubes 3 and 4. So tube 2 gave us a baseline for the experimental groups. Part B. Effect of Enzyme Concentration 1. How does the amount of enzyme (potato extract) used affect the activity? Explain. when there was more potato extract there was more activity which means that there was more foam 2.Why is it important to keep the reaction volume identical in all tubes? It is important to keep the reaction volume identical and have a baseline for before adding in the variable.