2Alecture+8

2Alecture+8 - Ac>va>on energies do not determine the...

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1/24/10 1 Lecture’8:Enzymes’ Inorganic’catalysts’ Enzymes’(and’other’proteins)’ Protein’structure’and’folding’ Measuring’enzyme’ac>vity’ Costs’associated’with’quality’control’ Average energy state (A + B) Transition state A+B->C+D Average energy (C + D) Progress of the reaction Ac>va>on’energies’ do’not’determine’the’direc>on’of’the’reac>on,’but’they’do’ aFect’its’rate.’ A+B’ ± > C+D’ C+D’ ± > ’A+B’ Average energy state (A + B) Transition state A+B->C+D Average energy (C + D) Progress of the reaction Distribution of energy among molecules If’the’average’energy’of’the’reactants’is’too’low,’very’few’molecules’will’make’it’ over’the’“ac>va>on’energy’barrier”’ Energy state (A + B) Transition state A+B->C+D (this stays the same) Average energy (C + D) (this will go up too) Progress of the reaction Activation energy shrinks Hea>ng’up’a’reac>on’will’speed’it’up,’as’heat’increases’the’G’of’all’ the’molecules’involved’ Energy of input compounds (A and B) RAISED Progress of a reaction Energy of products (C and D) RAISED Δ G Transition state is SAME A,B -> C,D Thus AT HIGHER TEMP, the KINETIC BARRIER DROPS (for both forward and back reactions) BUT the DIFFERENCE (the G) stays the same. But’this’is’not’a’viable’solu>on’for’living’things’ But’just’hea>ng’everything’up’increases’the’ rate’of’ all ’reac>ons-’it±ll’just’shorten’the’>me’ to’equilibrium’ Enzymes’(catalysts),’in’contrast,’provide’ speci²city’ They’also’ can be flipped on and of -’allowing’the’ cell’to’express’just’those’biochemical’pathways’ that’it’needs’at’the’moment’ Life’is’ALL’ABOUT’regula>on’of’metabolism-’and’ choosing’the’right’pathway’for’the’job.’
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1/24/10 2 Fermenta>on’ Pyruvate’oxida>on’ Respira>on’ glucose’-±’pyruvate’(glycolysis)’ ?’ Stay’in’cytoplasm’ Move’to’mitochondrion’ Citric’acid’cycle’ For’example…’ This’is’a’major’decision-’the’cell’must’interpret’ signals’from’the’environment,’and’then’ appropriately’tune’enzymes’and’transporters’up’ and’down.’ Catalysts’ Catalysts’take’part’in’a’reac>on,’and’speed’it’up,’but’ emerge’from’the’reac>on’with’no’permanent’chemical’ change.’ An’inorganic’example’is’solid’MnO 2 ,’which’will’very’ quickly’change’to’H 2 O 2 ’to’H 2 O’and’O 2 .’A’li_le’chunk’of’ MnO 2 ’can’last’you’a’life>me-’it’never’gets’“used’up”.’ Transi>on’metals’(metals’that’are’very’flexible’about’their’ oxida>on’state)’o²en’catalyze’ redox’reac>ons-’this’is’true’ for’biological’reac>ons,’too.’The’metal’provides’a’shortcut’
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2Alecture+8 - Ac>va>on energies do not determine the...

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