Exam 1 Review - Enzyme Kinetics & Hemoglobin and Myoglobin Binding answers

Exam 1 Review - Enzyme Kinetics & Hemoglobin and Myoglobin Binding answers

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Kaiser Imam September 23, 2007 BIOL 215 Exam 1 Review Enzyme Kinetics 1. Why does v max but not K m depend on the amount of enzyme used in an enzyme reaction? The velocity equation for v max includes the concentration of enzyme (actually, the concentration of enzyme active sites ): v max = k 2 [E] = k cat [E]; K m is a substrate concentration and is independent of the concentration of enzyme. 2. Write out the direct kinetic function. v o = ___V max [S] ____ [S] + K m 3. The following data were obtained by measuring the change in reaction rate in an enzyme- catalyzed reaction over time. The k cat for the enzyme is known to be 1500 min -1 . Find the K m and the total enzyme concentration value from the data below: [S] (mM) v o (μmol/min) 1.00 49 2.00 96 8.00 349 50.00 621 100.00 676 1000.00 698 5000.00 699 In this situation v max would be about 700, so therefore ½ v max would be 349. The corresponding [S] for that v o value is 8 M. Therefore, the K m value is 8 mM. To find the enzyme concentration use the equation v max = k cat [E]: v max = 700, k cat = 1500 [E] = v max / k cat = 700/1500 = 0.47 µmol. 4. What is the equation for the Lineweaver-Burk plot and what does it tell you? The direct kinetic plot has limitations since it depends on how accurately one can estimate the v max (the asymptote value). The Lineweaver-Burk plot, also called the double reciprocal plot, can be found by rearranging the direct kinetic function. 1/ v o = 1/ v max + (K m /v max ) (1 / [S]) The Lineweaver-Burk plot allows us to find K m and v max more accurately than the direct kinetic function. 1
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For a one-substrate, enzyme-catalyzed reaction Lineweaver-Burk plots were determined for three different enzyme concentrations . Which of the following three sets of plots would best describe this situation? The family of curves in b) would be expected to be obtained. If the total amount of enzyme ([E]) is increased, v max will increase since v max = k cat [E]. But remember that K m is unaffected by changes in enzyme concentration. Therefore, you should look for plots that show changes in v max without changes in K m , as is shown in b). 6. What is the equation for the Eadie-Hofstee plot? The Eadie-Hofstee graph plots (v o /[S]) against v o . The equation for the Eadie-Hofstee plot is v o / [S] = (v max /K m ) - (1/K m ) v o 7. What are the three types of inhibition? 1) Competitive: inhibitor and substrate compete for binding directly to the active site 2) Uncompetitive: inhibitor binds to an allosteric site only, making it more difficult for the substrate to bind to the active site 3) Noncompetitive: also called mixed inhibition; inhibitor binds in either of the forms described above 8. Modify the Michaelis-Menten mechanism to explain the various types of reversible inhibition and describe which type of inhibition is occurring in each. E
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Exam 1 Review - Enzyme Kinetics & Hemoglobin and Myoglobin Binding answers

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