MBB 321 Lecture Notes - Lecture 4: Enzyme Kinetics, New Taiwan Dollar, Reagent

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burgundyferret646

7 Oct 2015

School

Simon Fraser University

Department

Molec Biol & Biochem

Course

MBB 321

Professor

Ingrid Northwood

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Document Summary

A key factor affecting the rate of an enzyme-catalyzed reaction is the concentration of substrate [s]. The effect on the initial velocity (v0) of varying substrate concentration [s] can be monitored when the enzyme: at relatively low substrate concentrations, the initial velocity (v0) increases linearly with an increase in. The enzyme first combines reversibly with the substrate to form an enzyme-substrate (es) complex (this step is. The enzyme-substrate (es) complex then breaks down to yield the free enzyme and the reaction product (rate- E+p (the reverse reaction between e and p (k-2) is negligible. Rate-determining step: the slowest step in a reaction, whose rate determines the rate of the entire reaction. In an enzyme-catalyzed reaction, the enzyme can exist in two forms: uncombined form: free enzymes (e, combined enzymes: enzyme-substrate (es) complex, total enzyme [et]: free enzyme [e] + enzyme-substrate complex [es]

Related Questions

A 5 00Î¼l reaction co ntaining 0.5 pmol of an enzyme following Michaelis â Menten kinetics with saturating substrate concentration is studied . For this enzyme k1 = 1 x 10 9 M - 1 s - 1 , k - 1 = 2 x 10 3 s - 1 , and k2 = 1 x 10 5 s - 1 .

a . What is the Vmax for the enzyme considering that it has only one substrate binding site ? b. What are the values of Km and Ks? Is this a rapid equilibrium enzyme or does it follow steady state kinetics? Explain why .

c . What is the substrate concentration needed to achieve half maximal velocity? Explain the basis for your answer.

d . If the substrate concentration in part c is doubled , how many fold will the initial velocity increase?

e . What is the Km i f the concentration of the enzyme is doubled? f . What is the efficiency of this enzyme?

g. Would this enzyme be considered a perfect enzyme? Explain.

h . If 0.25 pmol of an irreversible or classic non - competitive inhibitor is added before starting the reaction. What is the resulting Km for the enzyme?

26. An enzymatic reaction proceeds with maximal velocity (Vmax) when A. the enzyme is in excess of the substrate. B. allosteric activators are present. the reaction is proportional to substrate concentration. D. the substrate concentration exceeds that of a noncompetitive inhibitor. E. the enzyme is saturated with substrate 27- An enzymatic reaction proceeds with maximal velocity (Vmax) when A. the substrate concentration is equal to that of a competitive inhibitor B. allosteric effectors are present. C. the enzyme substrate complex is maximal. D. the substrate concentration exceeds that of a noncompetitive inhibitor. E. all of the substrate is bound to the enzyme. 28. An enzyme affects the rate of a chemical reaction by A. decreasing the free energy change of the reaction. B. increasing the free energy change of the reaction. C. lowering the energy of activation of the reaction. D. displacing the equilibrium constant. E. raising the energy of activation of the reaction. 29. Which statement is CORRECT? A. Enzymes are small molecules that are heat stable. B. Enzymes affect rates of reactions in the forward and reverse direction. C. Enzymes will determine whether a reaction will take place. D. Enzymes are permanently altered following the conversion of substrate to product. 30. Which of the following statements is TRUE? Enzyme catalysis of a chemical reaction: A. increases the energy of the transition state. B. decreases the change in free energy of the reaction. C. increases the change in free energy of the reaction. D. decreases the change in the free energy of activation. 31. Which of the following statements about enzyme substrate complexes is TRUE? A. At high substrate concentration the rate of the reaction is first order. B. The enzyme concentration is higher than the substrate concentration under physiological conditions. C. Alteration in the conformation of the enzyme may occur when substrate binds. D. Increase in enzyme concentration does not affect the rate of the reaction. 32. All of the following statements about enzymes are correct EXCEPT A. enzymes are usually protein in nature and cause reactions to occur B. enzymes form complexes with substrates and products C. enzymes affect the rate of reactions and are not permanently altered during a reaction D enzymes can undergo structural modification during a reaction E. enzyme specificity requires specific functional groups on the enzyme and substrate

33-To stabilize the transition state complex, which of the following must be lowered? A) Initial energy state B) Activation energy C) Net energy change D) The Vmax B) Final energy state 34- Which of the following statements about allosteric enzymes is CORRECT? A The binding of substrate to any active site affects the other active sites B The plot of initial velocity vs. substrate concentration is a straight line C The Keq of the reaction is increased when allosteric activator is bound D The enzymes contains only one polypeptide chain E Allosteric activators bind to all active sites equally 35. Which statement about the two different models proposed to explain enzyme specificity is CORRECT. a. The substrate changes shape when enzyme binds in the Lock and Key Model. b. The enzyme undergoes a covalent modification when bound to substrate in the Lock and Key Model. c. The active site of the enzyme alternates in conformation between opened and closed in the Induced Fit Model. d. The enzyme changes conformation after binding the substrate in the Induced Fit Model. eÂ·The product structure is altered after it has bound to the enzyme in the Induced Fit Model. 36. An enzymatic reaction proceeds with maximal velocity (Vmax) when A. the substrate concentration is equal to that of a competitive inhibitor. B. allosteric effectors are present. C. the enzyme substrate complex is maximal. D. the substrate concentration exceeds that of a noncompetitive inhibitor. E. all of the substrate is bound to the enzyme. 37. Which of the statements below are incorrect? A With all other factors that modify the rate of the enzyme catalyzed reaction remaining constant as we raise the temperature of an enzyme catalyzed reaction there is an initial increase of velocity with temperature. B. The rate of reaction increases with temperature because there is an increasing number of molecules with sufficient energy to pass over the energy barrier which we call the energy of activation C. Reaction rate increases with temperature until a maximum is reached, when the rate of the reaction will suddenly suddenly fall to zero because the enzyme will be denatured and therefore inactive. D. The reaction rate initially increases as temperature rises owing to increased kinetic energy of the reacting molecules E. Enzymes in crease reaction rates due to their ability to lower the energy barriers for reactions F. None of the above 38- Which of the following is true for the induced fit theory of enzyme action? A. The conformation of the substrate changes before binding to the enzyme. B. The active site changes shape during binding of the substrate C. The substrate fits into a preformed active site through a lock-and-key mechanism. D. Enzymes alternate between conformations where the active site is either open or closed. E. The substrate causes a cleft to form in the enzyme where it subsequently binds

MBB 321 Lecture Notes - Lecture 4: Enzyme Kinetics, New Taiwan Dollar, Reagent

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