BCHM 307 1st Edition Lecture 13Outline of Last Lecture I. Enzyme ReactionII. Enzyme Rate EquationIII. Michaelis-Menten PlotA. Definition of Enzyme VelocityIV. Velocity EquationA. Michaelis ConstantOutline of Current Lecture I. Km and VelocityA. Velocity EquationII. Allosteric Enzyme ReactionsA. Sigmoidal CurveB. Allosteric Chain ReactionIII. Enzyme Kinetics GraphsA. How to Plot the GraphB. Reverse ReactionCurrent LectureWe 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= ½ 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/2These 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 changetheir 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
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