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CHMB62H3 (2)

Chapter 5 & Chapter 6 & Chapter 7 .docx

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University of Toronto Scarborough
John Glover

Chapter 5 (5.1, 5.2, 5.3, 5.4) 5.1  Enzyme accelerate reactions by factor of as much as a million or more  Highly specific both in the reactions that they catalyze and in their choie of reactants (substrates)  The specificity of an enzyme is due to the precise interaction of the substrate with the enzyme which is a result of the intricate three-dimensional structure of the enzyme protein 5.2  And enzyme without ite cofactor is reffed to as a apoenzyme the complete catalytically active enzyme is called a haloenzyme  Cofactors can be divided inot two groups 1)small organic molecules called coenzymes and 2)metals 5.3  Enzyme speed p the rate of chemical reactions but the properties of the reaction  Free energy (G) is the thermodynamic property that is a measure of useful energy or energy that is capable to doing work  The free energy difference ( G) between the products and the reacts o Tells us whether the reaction can take place spantaneously o A reaction can take place spontaneously on if G is negative  Releases energy or exergonic o If a reaction can no take place spontaneously if G is positive  And input of energy is required to drive the reaction endergonic  The G is independent of the path of the transformation  The G provides no information about the rate of the reaction  The free energy required to initiate the conversion of reactants into products A + B C + D  G = G + RTln [C][D]/[A][B]  G is the standard free energy change  the simple way to determine G ’ (standard free energy change at pH 7) is to measure the concentrations reactants and products when the reaction has reached equilibrum. At equilibrum there is no net change in the concentration of reactants and porducts and there for G=0  G = -RTln [C][D]/[A][B]  K’eq[C][D]/[A][B] - G /RT  K’eqe 5.4  The interaction if the enzyme and substrate at the active site promotes the formation of the transition state o The active site is a three-dimensional cleft or crevice o The active site takes up a small part of the total volume of a enzyme o Active sites are unique microenvironments o Substrates are bound to enzymes by multiple weak attractions o The specificity of binding depends on the precisely defined arrangement of atoms in an active site Chapter 6 (6.1, 6.2, 6.3,) 6.1  Kinetics- The study of the rates of chemical reactions  The rare of the reaction V id the quantity of A that disappears in a specified unit of time t. it also equals the rate of the appearance of product P. A P  V=-d[A]/dt=d[P]/dt  The rate of the reaction is directly related to the concentration of A by a prportionality constant k called the rate constant  V=k[A] Reactions in which the rate is directly proportional to the reactant concentration are called first-order reaction with unit os s (per second)  Second order reactions or bimolecular reactions 2A P A + B P  V=k[A] or V=k[A][B] the rate constants called second order rate constants -1 -1 have the units M s (per mole per second) 6.2  The rate of cataysis Vowhich is defined as the nuber of moes of products formed per second varies with the substrate concentration [S]  When enzyme concentration is constant  An enzyme E that catalyzes the conversion of S to P by the following reactions E +S ES E + P  Where k i1 the rate constant for the formation of the enzyme-substrate (ES)complex, k 2s the rate constant for the formation of the product P and K -1 and K -2e the constants for the respective reverse reactions.  The amount of of product formed increase with time  Eventually a rime is reached when there is no net increase in the concentration of S or P o The enzyme is still actively converting substrate into product and visa versa but the reactions equalibrum has been attained  V 0s determined for each substance concentration by measuring the rate of product formation at the early times before P accumulates  The simplified reaction scheme E + S ES E + P  Michaelis-Menten equation escribes the variation on enzyme activity as a function of substrate concentration V0=V max[S]/[S] +KM where K M(k +-1)/2 & 1 maxk 2E} T  Vmax is attained only when alll of the enzyme is bound to substrate o Directly dependent on enzyme concentration o At very low substate concentrations when [S] is much less thean the value of M the rate is directly proportional to the substrate concentration V =(V /K )[S] 0 max M o At high substrate concentrations when [S] is much greater the K M V0 Vmaxat this level the enzyme is said to be saturated  When V =V /2 means that [S]=K 0 max M  The Michaelis-menten equation can be transforming into one that ive a straight like by taking the reciprocal of both sides of the equation 1/V =K /V 1/S + 1/V 0 M max max  The K Malue for an enzyme depends on the enviromental condition  Vmaxis the number of substrate molecules that an enzyme can convert into a product per unit time when the enzyme is fully saturated with substrate Vmax=k2[E]T  When [S] KMThe enzyme rate is much less the k catbecause most of the active site are unoccupied and the amount of free enzyme is nearly equal to the total concentration of enzyme [ET V0=k cat[M][S]  Kcat iM a measure of the catalytic efficiency  Multiple-substrare reactions can be divided into town classes o Sequential reactions  All substrates bind to the enzyme before the product is released  In a bisubstrate reaction a ternary complex consisting of the enzyme and both substrates forms o Double displaceent  in double displacement one or more products are releases before all substrates bid the enzyme  defining feature is the existence of a substituted enzyme intermediate 6.3  allosteric enzymes- enzymes that regulate the flux of biochemicals through metabolic pathways o features include; regulation of catalytic activity by enviromentsal signals, including the final product of the metabolic pathew
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