BCHM 307 1st Edition Lecture 13 Outline of Last Lecture I Enzyme Reaction II Enzyme Rate Equation III Michaelis Menten Plot A Definition of Enzyme Velocity IV Velocity Equation A Michaelis Constant Outline of Current Lecture I Km and Velocity A Velocity Equation II Allosteric Enzyme Reactions A Sigmoidal Curve B Allosteric Chain Reaction III Enzyme Kinetics Graphs A How to Plot the Graph B Reverse Reaction Current Lecture We will continue to look at enzyme kinetics in this lecture Last lecture we defined the Michaelis constant Km Km can also be defined based on what velocity the enzyme operates at Km is the concentration of the substrate when the enzyme is working at the point that is half of the maximum velocity This can be said using a formula as follows Km S where Vo Vmax Vo is the initial velocity This equation can also be derived as shown below If S Km and V Vmax S Km S Then V Vmax S 2 S Therefore V Vmax 2 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Not all enzymes behave in the way described by Michaelis Menten though It is true for all enzymes that the substrate concentration determines the velocity of the catalysis Some enzymes behave in an allosteric manner This means that the first substrate binding event is slow The binding of the substrate to the first enzyme causes other enzymes next to it to change their conformation This shape change will allow other substrates to bind more easily to the enzyme This chain reaction will trigger faster substrate binding with the enzyme If you were to graph the velocity vs the substrate concentration a sigmoidal curve would form This can be contrasted with the typical hyperbolic curve we saw in previous lectures The sigmoidal relationship is due to the enzyme activity jumping from low to high and then leveling off For either type of enzymes it is important to understand how these graphs are formed Biochemists first decide on a set of substrate concentration values These values will go on the X axis They will use the same enzyme concentration throughout the measuring process The velocity of the catalysis reaction will be measured at each substrate concentration level The velocity values are plotted on the Y axis From the curve drawn the Km and Vmax can be determined using the equations described above It is also important to note that in these plots the reverse reaction is not a consideration
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