PS9B

docx

School

Brooklyn College, CUNY *

*We aren’t endorsed by this school

Course

376

Subject

Chemistry

Date

Feb 20, 2024

Type

docx

Pages

6

Uploaded by meem437

Report
CHM 376 Biochemistry I Fall 2023 Problem Set 9B: Enzyme Kinetics 1. Define the following terms: kinetics and chemical kinetics . 2. What is the meaning of the term rate enhancement? 3. Can enzymes make unfavorable reactions favorable ? Do enzymes change K eq ? How can a thermodynamically unfavorable reaction be made favorable? 4. What is the approximate range of rate enhancements observed in enzymes? 5. Why is the study of kinetics useful in understanding the stabilization of the transition states by enzymes? 6. What is site directed mutagenesis and how can it be used to investigate the mechanism of transition state stabilization by enzymes? 7. How can enzyme kinetics be used to understand the role of an enzyme within a cell? How can enzyme kinetics be used to optimize the (research, clinical, and industrial) laboratory use of enzymes? 8. How do catalysts accelerate the rate of a reaction? Use a plot of kinetic energy (x axis) and number of molecules (y axis) to explain your answer. Then use transition state theory to answer the same question. 9. Show that the bimolecular association rate constant ( kinetic ) has units of M -1 s -1 , that the unimolecular dissociation rate constant ( kinetic ) has units of s -1 . Using the relationship between these two different rate constants, what are the units of the dissociation constant ( thermodynamic )? 10. Write the K D (or K d , as it means the same thing) for myoglobin in terms of association and dissociation rate constants. ( This is the same question as #5 but phrased slightly differently ). 11. What do we mean by the phrase, “the binding constant is determined by how fast things come together and how fast they fall apart”? 12. Explain the phrase, “myoglobin can do two things, but enzymes can do three things”. What are the two things that myoglobin can do and what is the one thing enzymes can do that myoglobin cannot? 13. Write the equation for in terms of k a (or k 1 , the same thing) and k d (or k -1 , the same thing), and [L].
14. What is the Brown-Henri hypothesis? How does the Brown-Henri hypothesis relate enzyme function to myoglobin? What is different between an enzyme and a protein like myoglobin? Why, according to Brown and Henri, is there a point where increasing the concentration of substrate does not increase the rate at which product is formed? 15. What is the steady state assumption ? How does it differ from the equilibrium assumption? According to either assumption does the concentration of ES change during enzyme catalysis? 16. Write the mathematical rate model for the Brown-Henri hypothesis. There are three rate constants ( assuming catalysis is irreversible ). What chemical reaction does k 1 describe and what are its units? What does k -1 describe and what are its units? What does k 2 describe and what are its units? How is an enzyme, according to Brown and Henri, like myoglobin? How is it different? 17. Write the M-M equation. Why is an M-M plot of M-M kinetics hyperbolic? 18. Write an equation for V max in terms of enzyme amount (or concentration) and k 2 . Under what conditions does the observed rate equal V max ? 19. Define V max . What is the turnover number ? What are the units of turnover number ? What are the two potential units for V max , and in what way are they similar and different? How does V max depend on [S]? How does V max depend on [E t ]? How many more ways can I ask the exact same question? 20. Using relatively simple experiments, is it possible to determine the value of k 1 and k -1 ? 21. Write an equation in terms of rate constants that describes the fraction of enzymes bound by substrate. Show that the units of this expression (called K M ) are concentration. Show that when [S] = K M , v o = V max /2. 22. Assuming K M = 2mM, at what concentration of [S] would v o = 0.36 X V max ? 23. Is K M an intrinsic property of an enzyme or does it describe a specific enzyme-substrate pair? Can an enzyme have more than one K M value? 24. What information can be obtained from analyzing a progress curve? How do we obtain the data to create a progress curve. Is the entire progress used to obtain this information, or is the analysis restricted to a subset of the entire data? Explain why this is. 25. How is data obtained from a progress curve? What is the relationship between the initial slope of the data on a progress curve and the rate of a chemical reaction. 26. What information is presented on an M-M plot? What is the general shape of the data plotted on an M-M plot? Use your knowledge of receptor-ligand interactions to speculate why this is.
27. Write the full Henri-Michaelis-Menten equation of enzyme kinetics, including the rate constants for each step. Check the Michaelis-Menten equation on your fact sheet. Notice that it does not include the full expression including all rate constants. This means that you must know how each term is expressed in terms of rate constants. 28. What is a progress curve ? What are on the x- and y- axes of a progress curve ? Why is the progress curve approximately hyperbolic ? How do we properly obtain the rate of a chemical reaction from a progress curve? Why do we only use the initial portion of the Progress Curve to obtain data for out M-M plot? 29. Explain the following statement: the observed rate of an enzyme catalyzed reaction is equal to the rate of the chemical step times the fraction of the enzymes bound to substrate . 30. Using the full M-M equation, show that at high substrate concentration [S] >>> (k -1 + k 2 ) / k 1 )), that the rate of the enzyme catalyzed reaction = k 2 [E t ] where k 2 is the rate of the chemical reaction step (product formation) and [E t ] is the concentration of enzyme. Explain why we call this value V max ? 31. Use the M-M equation to show that the units of the rate are the same as the units used to calculate V max , not the units used to calculate K M . 32. What is the distinction between the rate law for enzyme catalysis of a substrate at low substrate concentrations and high substrate concentrations? ( The answer to this question is not explicitly in the PowerPoint. You need to think this one through .) 33. How does the Brown-Henri model (hypothesis) account for the shape of the M-M plot of the enzyme invertase ? 34. Draw a set of ideal progress curves showing three different concentrations of substrate [S 1 ] > [S 2 ] > [S 3 ]. Explain, in no more than 3 sentences how useful information is extracted from this graph. Next, construct an M-M plot for an enzyme following ideal M-M kinetics, showing how the data extracted from the progress curves is used to construct the M-M plot. Label the position of K m and V max on your plot. As you work on this problem recall the distinction between an M-M plot and an enzyme following M-M kinetics. Also remember that the similarity in the appearance of the Progress Curve and the M-M plot showing M-M kinetics is entirely superficial. Do not confuse a Progress Curve with an M-M plot. 35. Why does the M-M plot of an enzyme that follows M-M kinetics show zero order kinetics at high substrate concentration? 36. What is K m ? Write K m in terms of the rate constants from the H-M-M model of enzyme- catalyzed reactions? What is K m a measure of? How can we use K m to determine the fraction of enzymes that are actively processing substrate into product? ( Note: you will no t be given this equation on an exam. This is something you must know ). Given an M-M plot, how can we find K m ? What is the major challenge associated with the approach you just suggested?
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help
37. Consider the following data obtained from an enzyme catalyzed reaction: V o ( mol/min) substrate added ( mol/L) 217 0.8 325 2 433 4 488 6 647 1000 648 1500 What is the approximate K m for the enzyme? Explain your answer. Do not perform a calculation for this problem. Use a reasonable approximation . 38. Two different enzymes are able to catalyze the same reaction A B. They both have the same V max but differ their K m for substrate A. For enzyme 1, the K m is 1.0 mM. For enzyme 2, the K m is 10 mM. When enzyme 1 was incubated with 0.1 mM A, it was observed that B was produced at a rate of 0.0020 mmols/minute. (a) What is the value of V max of the enzymes? (b) What will be the rate of production of B when enzyme 2 is incubated with 0.1 mM A? (c) What will be the rate of production of B when enzyme 1 is incubated with 1 M A. Can you explain your result for (c) and why it did not require you to actually do any additional math ? 39. What is V max ? Provide both a mathematical and written description of V max ? How can V max be experimentally altered? How can we use V max to determine the turnover number (k cat ) of an enzyme-catalyzed reaction? What is the major challenge of determining V max from an M-M plot? ( I have asked this question several times on this Problem Set in a variety of ways. Make sure you can recognize the different ways we can use/interpret V max . In particular, make sure you can make a high-quality estimate of V max from looking at kinetics data, and use this V max as the basis for more complex calculations ). 40. Why is it challenging to obtain the parameters V max and K m from a M-M plot? Explain the Lineweaver-Burk approach to determining the parameters V max and K m of an enzyme-catalyzed reaction.
41. An enzyme, known to follow M-M kinetics, was studied and the following data was obtained: [S] mM Rate Product Formed ( mol/min) 1.5 0.21 2.0 0.24 3.0 0.28 4.0 0.33 8.0 0.40 16.0 0.45 Use L-B analysis to determine K m and V max of this enzyme acting on substrate. ( You will need computer-graphing software, such as EXCEL, to complete this problem. On an exam, a graph may be provided for you, but you might still need to label each axis and interpret the parameters from the graph. ). 42. How do we define the catalytic efficiency of an enzyme? Which parameter is the best measure of the catalytic efficiency, and why? Calculate the catalytic efficiency for the enzyme from Problem #41. 43. Show, using the M-M equation, that when [S] >>> K m , v o = V max . Show, using the M-M equation that when [S] <<<K m , v o =[S][E t ]k cat /K m . Explain the significance of the M-M under both high and low substrate conditions. 44. What is catalytic perfection ? What physical phenomenon defines the upper limit on how fast an enzyme can convert a product into substrate? How does this phenomena drive the evolution of enzymes that participate in channeling? Use the M-M equation to show that the limit on efficiency is the rate of binding the substrate to the enzyme. 45. Write the equation for the random TCM and the ordered TCM models, including all rate constants. What is the major distinction between the random TCM and the ordered TCM? 46. Write the equation for the Ping-Pong (PiPo) model of enzyme kinetics. What is the major distinction between the random/ordered type kinetics and Ping-Pong kinetics?
47. A true story. An enzyme can catalyze a reaction with either of 2 substrates, S 1 or S 2 . The K m for S 1 was found to be 2.0 mM and the K m for S 2 was found to be 20 mM. A student determined that the V max was the same for the two substrates. Unfortunately , she lost the page of her notebook and needs to know the value for V max . She carried out two reactions, one with 0.1 mM S 1 and the other with 0.1 mM S 2 . Unfortunately , she forgot to label which reaction tube contained which substrate. Determine the value of V max from the results she obtained. Tube Number Rate of Formation of Product 1 0.5 2 4.8 48. An enzyme catalyzes a reaction at a velocity of 20 mol/min when the concentration of substrate (S) is 0.01 M. The K m for this substrate is 1 X 10 – 5 M. Assuming that Michaelis-Menten kinetics are followed, what will the reaction velocity be when the concentration of S is (a) 1 X 10 – 5 M and (b) 1 X 10 – 6 M? 49. When 10 g of an enzyme of Mass (M r ) 50,000 g / mol is added to a solution containing its substrate at a concentration one hundred timed K m , it catalyzes the conversion of 75 mol of substrate into product in 3 minutes. What is the k cat (k 2 ) of the enzyme? Recall that k cat and k 2 are, for our purposes, equivalent. 50. The muscle enzyme lactate dehydrogenase catalyzes the reaction: pyruvate +NADH + H + lactate + NAD + . Solutions of NADH, but not NAD + , absorb light at = 340 nm. Explain how this phenomenon could be used to design an enzyme activity assay for lactate dehydrogenase . Note that the answer to this question is not in the PowerPoint. You need to use your prior knowledge of biochemistry concepts to work through this problem, as it involves concepts that span multiple topics. Discuss your approach with your recitation group before speaking with your instructor.
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
  • Access to all documents
  • Unlimited textbook solutions
  • 24/7 expert homework help