Essential Elements of Biochemistry BCHM 3050 Dr Srikripa Chandrasekaran Lecture 2 2 15 2 4 15 Notes Enzymes Part 2 Kinetics I II Liquidy candy syrup A Invertase makes candies more creamier than granular more liquidy than solid Invertase an enzyme that catalyzes the hydrolysis breakdown of sucrose table sugar B Enzymes are easily manipulated Velocity and affinity A Velocity the rate of a reaction B Affinity of the enzyme how strong the enzyme binds to the substrate C Mode of regulation the cell can control the mode of regulation of enzyme activity III Substrate concentration has the greatest effect A Must have a substrate in order to have a reaction In order for the enzyme to function you need to have a substrate Normally more and more reactants allows the enzyme reaction to go faster Velocity rate of enzyme reaction B For a good enzyme once the enzyme gets saturated you can continue to add more and more substrate but the enzyme will not exceed its maximum velocity once it hits it Substrate concentration that corresponded with half of the enzyme s maximum velocity is called Km the Km tells you how good the enzyme is and what the maximum velocity of the enzyme is going to be Given just one of these 3 variables should enable you to figure out the other 2 variables C Initial velocity is fastest The dashed line enzyme does not exist but it is the dream enzyme Enzymes that do exist have maximum velocities so they can only work up to a set speed we do not want them to work beyond their maximum velocities because that could potentially cause harm to the organism The closer the curve is to the dashed line the better the enzyme Grade of an enzyme how much substrate is consumed per minute or any unit of time Molarity moles liter D Importance of Vmax Km Vmax and Km define all enzymes Enzymes rarely operate at their true maximum there usually is not enough substrate around to reach the Vmax Enzymes usually work at half their maximum velocity Km 1 Km how tightly an enzyme will bind to a substrate The x axis of a graph represents the concentration of substrate usually and this is measured by mM or mmolesl 1 The y axis of a graph usually represents the velocity rate and this is measured by mMs 1 Ex If Km is 20mM Vmax 2 is 35 mMs 1 then Vmax is 70 mMs 1 E Significance of Km Km affinity of the enzyme The lower the Km the better for the enzyme The lower the Km means the lower the Vmax and this is good for the enzyme because you do not want the enzyme to waste energy If the Vmax is low it will take less energy for the enzyme to reach its ideal max velocity thus it will be able to produce products as fast as it possibly can while using a low amount of energy The lower the Km the higher the substrate affinity tighter the substrate will bind to the enzyme F Experimental determination of Vmax Km Refer to graph shown in corresponding PowerPoint 5 Graph allows estimation of Vmax Km Estimations would be easier if working with a straight line Lineweaver Burk plots are linear transformations of hyperbolic plots G The Michaelis Menton Equation Leonor Michaelis and Maud Menten developed the hyperbolic relationships and their equation in 1907 Michaelis Menton equation can be used to predict the velocity of a reaction at a given substrate concentration assuming you know the the Km Vmax constants This equation gives you the relationship between Km Vmax substrate and velocity V Vmax S S Km H Lineweaver Burk Plots Lineweaver Burk developed their double reciprocal plot in 1934 They changed the equation slightly in order to avoid having to round the end number rounding was initially required because it is a curve Lineweaver and Burk do the reciprocal of the Michaelis Menton Equation 1 V Km Vmax S 1 Vmax Lineweaver and Burk Equation The advantage of the Lineweaver and Burk Equation is that it fits the equation y mx b slope equation You get crisp numbers do not have to round up 2 3
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