Lecture'15'–Chapt'16'Glycolysis'“Living'organisms,'like'machines,'conform'to'the'law'of'conserva?on'of'energy,'and'must'pay'for'all'their'ac?vi?es'in'the'currency'of'catabolism.”'Ernest'Baldwin'Dynamic'Aspects'of'Biochemistry'''Louie'Pasteur’s'scien?fic'inves?ga?ons'into'fermenta?on'of'grape'sugar'were'pioneering'studies'of'glycolysis.'1'OUTLINE''v 'Glycolysis'M''First'phase'M'Reac?ons'1M5'(no'ATP'generated)'M''Second'Phase'–'Reac?ons'6M10'(genera?on'of'ATP)'v 'Feeder'pathway'to'glycolysis'(other'sugars'can'also'enter'the'glycoly?c'pathway)'v 'Regula?on'of'glycolysis'v 'Glucose'transporters'v 'Fate'of'pyruvate'under'anaerobic'condi?ons'M''In'yeast:'Alcohol'fermenta?on'M In'other'microorganisms'and'exercising'muscle:'Lac?c'acid'fermenta?on'v 'HypoxiaMInducible'Factor'2'Metabolic'pathways'are'compartmentalized'within'cells'Phase'1'Phase'2'Glycolysis'pathway'common'to'both'prokaryotes'and'eukaryotes.''In'eukaryotes,'glycolysis'takes'place'in'cytoplasm'3'~'25'ATP'Glucose'is'converted'to'glyceraldehyde'3Mphosphate'(GAP)''5'steps:' '1.'Phosphoryla?on'of'glucose''''2.'Isomeriza?on'''''3.'Second'phosphoryla?on'of'FructoseM6P''''4.'Cleavage'into'two'3Mcarbon'molecules''''5.''Isomeriza?on'of'DHAP'to'GAP'1st'Stage'of'Glycolysis'Uses'2'molecules'of'ATP/glucose'but'makes'no'ATP.''Traps'and'prepares'glucose'for'following'oxida?on'steps'4'Glycolysis:''Reac?on'1'M'Phosphoryla?on'+'Mg+'5'ATP'+'H2O'''''''''''''ADP'+'Pi'' ''''''''∆G°’reac?on'1'='M30.5'kJ/mol ''glucose'+'Pi''''''''''''GM6MP'''+'H2O ' '∆G°’reac?on'2'='+14'kJ/mol'glucose'+'ATP'''''''''''GM6MP'+'ADP'''' '∆G°’overall'='M16.5'kJ/mol'Glucose'is'kept'in'the'cell'by'phosphoryla?on'to'glucoseM6Mphosphate'6'Hexokinase'7'Glycolysis:''Reac?on'2'–'Isomeriza?on'by'phosphoglucose'isomerase'8'Glycolysis:''Reac?on'3M'Second'Phosphoryla?on'Phosphofructokinase'(PFK/PFK1)'9'Glycolysis:''Reac?ons'4'–'Cleavage'of'one'6Mcarbon'to'two'3Mcarbon'molecules'10'Glycolysis:''Reac?ons'5''M'end'of'1st'phase'of'glycolysis'11'GAP'is'converted'to'pyruvate:''5'steps:' '6.'''Oxida?on'of'GAP'to'1,3BPG''''7.'''Phosphoryla?on'of'ADP''''8.'''Mutase''''9.'''Dehydra?on'by'Enolase''''10.'Phosphoryla?on'of'ADP,'giving'pyruvate'Second''Stage'of'Glycolysis'The'three'carbon'units'are'oxidized'to'pyruvate,'genera?ng'4'molecules'of''ATP/glucose'and'2'NADH/glucose'12'Glycolysis''Reac?on'6''''M'''''GAP''is'oxidized'to'1,3MBPG'13'∆G°’'='M50'kJ'molM1'∆G°’'='~'+56'kJ'molM1'Uncoupled'Oxida?on'and'Phosphoryla?on'Reac?ons'14'Coupling'of'the'two'processes'(by'one'enzyme)'allows'the'conserva?on'of'energy'released'by'oxida?on'∆G°’'='+6.3'kJ/mol'15'16'Molecules'with'HighMPhosphoryl'Group'Transfer'Poten?al'Glycolysis:''Reac?on'7'(ATP'producing'reac?on)'2'ATP'consumed'in'the'1st'phase'of'glycolysis'(Reac?ons'1'and'3)'are'‘paid'off’'in'the'this'step'of'the'2nd'phase'of'glycolysis.'2X/glucose'2X/glucose'17'The'forma?on'of'the!highMphosphoryl'group'transfe'rpoten?al'compound'''1,3MBPG'(in'step'6)'is'essen?al'as'a'prepara?on'for'the'ATP'produc?on'(in'step'7).' GAP 1,3-BPG 3 PG Preparative step for ATP production in the following step ATP Step 6 Step 7 Actual ATP production Thermodynamically'favorable'Reac?ons'7'drives'the''less'favorable'Reac?on'6'∆G°’'='+6.3'kJ/mol'∆G°’'='M49.6'kJ/mol'30.5'kJ/mol'M18.9'kJ/mol'18'Compound!with!High/Phosphoryl!Group!Transfer!Poten:al!Glycolysis:''Reac?on'8'–'Phosphoglycerate'Mutase'(Note:''The'term'Mutase'is'applied'to'those'enzymes'that'catalyze'migra?on'of'func?onal'groups'from'one'posi?on'to'another'on'the'same'substrate'molecule)'19'Glycolysis:''Reac?on'9'M''Dehydra?on'of'2MPG'ΔG°′ = +1.8 kJ/mol 20'21'Molecules'with'HighMPhosphoryl'Group'Transfer'Poten?al'Glycolysis:''Reac?on'10'M'ATP'synthesizing'reac?on''(Regulated'step)' ΔG°′ = -31.7 kJ/mol after removing the energy used to phosphorylate ADP'Pyruvate'kinase'(Ketone'form)'22'The'free'energies'of'the'reac?ons'of'glycolysis'under'standardMstate'condi?ons.'hexokinase'PFK'Pyruvate'kinase'ΔG°′'23'The'free'energies'of'the'reac?ons'of'glycolysis'under'actual'intracellular'condi?ons'in'erythrocytes.'∆G'='M96'kJ'molM1'hexokinase'PFK'Pyruvate'kinase'∆G'24'The'net'reac?on'for'glycolysis'is'∆G°’='M'96'kJ'molM1'25'Entry'points'in'glycolysis'for'galactose'and'fructose.'26'Fructose'enters'the'glycoly?c'pathway'in'the'liver'through'the'fructose'1Mphosphate'pathway.'27'Fructose'can'be'converted'to'FM6P'by'hexokinase.'hexokinase'28'Galactose'enters'the'glycoly?c'pathway'in'the'liver'through'the'glucose'6Mphosphate'pathway.'29'Glycosyltransferase'Reac?on'GM6P'phosphoglucomutase'glycolysis'30'31'Regula?on'of'Glycolysis'is'CellMType'Dependent'Muscles'use'glucose'for'fuel'(ATP)'–'to'power'muscle'contrac?on'Liver'uses'glucose'to'maintain'blood'sugar'level.'Regula?on'of'Glycolysis'Enzymes'catalyzing'irreversible'reac?on'in'metabolic'pathways'are'poten?al'control'sites.'• 'hexokinase'• 'phosphofructokinase'• 'pyruvate'kinase'32'Muscle'contains'Hexokinase!I'while!liver!contains'Hexokinase!IV!(Glucokinase).'''This'is'to'adapt'to'the'different'roles'of'muscle'and'liver.''Vmax '2 Km (hexokinase) = 0.03 mM Km (glucokinase) = 10 mM Hexokinase versus Glucokinase
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