MCB 450 1st Edition Lecture 11Outline of Last Lecture I. Principles of Enzyme Catalysisa. Free Energy and Equilibriab. Keq and ΔG in Living Cellsc. Activation Energyd. Enzyme-Substrate InteractionOutline of Current Lecture I. Effect of [substrate] and [enzyme] on reaction rateII. Km and VmaxIII. KcatIV. kcat / KmV. Bi-substrate reactionsCurrent LectureBig Picture-S -- substrate-P -- product-E -- enzyme11-18-Small Km --> low S-Large Km --> high SDetermination of Km and Vmax from double reciprocal plot-Know this for exam questions11-22-Illustrates the different enzymes and whether they have large or small Km'sGeneralization about Km-Km of an enzyme for its substrate is often near the concentration of that substrate in the cellKcat: rate constant for the rate-limiting step in an enzyme-catalyzed reaction-Km's and Kcat's can vary drastically between enzymesProblem-Expect higher impact on activity-If total amout of E is increased, Vmax will increase because Vmax = k2[E1] (or kcat [E1}.-But, km = (k1 +k2) which is independent of [E], so, will km be the same or different?oKm will be the same-B is the correct graph11-29These 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.-Can use kcat and km to compare enzymes11-30-Chymotrypsin prefers bulkier substrates like phenylalanine-The different values of kcat/km tells us which is the better substrate for chymostrypsinoThe higher the number the betterWhen kcat/Km tells us about an enzyme-If enzyme binds the substrate too well then you can make the reaction rate lower and increase the activation energy-Know slide at end of lecture that has all of the different forms of these equationsSolving kcat and kcat/Km problems- Given Vmax = 75 umoles/3 min = 25 umoles min-1-[Et] = 10 = 10 2g/5x10^4 g mol-1 = 2 x 10^-7 moles-Kcat = Vmax/[Et] = 2.5 x 10 -5 moles min-1/2 x10^7 moles -= 1.25 x 10 ^2 moles/minoThe sort of calculations we might get on the examPing-pong reaction: covalently modified enzyme = intermediate-Chymotrypsin can be categorized as a ping pong
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