3. Application of the free energy ( concept to biochemical reactions. G): the amount of energy available to do work during a reaction at a constant temperature and pressure: change, not absolute value can be measured The free energy difference between the products and the reactants Gibbs observation: under constant temperature and pressure, all systems change in such a way that free energy is minimized(products should have less free energy than reactants for a reaction to occur spontaneously, i. e, 4G has a negative o value
3. Application of the free energy (G) concept to biochemical reactions • Free energy (G): the amount of energy available to do work during a reaction at a constant temperature and pressure; change, not absolute value can be measured. • Free energy change (G): The free energy difference between the products and the reactants. • Gibbs observation: under constant temperature and pressure, all systems change in such a way that free energy is minimized (products should have less free energy than reactants for a reaction to occur spontaneously, i.e., G has a negative value )
ta neit has nothing to do with rate in biochemist ) value of the change in free energy under conditions of 298K(25 C), I atm pressure, pH 7.0(chemists use pH O, 1.e, the concentration of H they use is IM not 10-7M as biochemists use here) and initial concentrations of 1 M for all reactants and products(except H The depends on 4G"o, temperature, ratio of product and reactant concentrations(Q): FO.LG- AGo+ RTIn Q Enzymes only speed up thermodynamical favorable reactions(having a negative 4G
• Spontaneity has nothing to do with rate! • Standard free energy change in biochemistry (G' o ): value of the change in free energy under conditions of 298 K (25oC), 1 atm pressure, pH 7.0 (chemists use pH 0, i.e., the concentration of H+ they use is 1M, not 10-7 M as biochemists use here) and initial concentrations of 1 M for all reactants and products (except H+ ). • The actual free energy chang (G )depends on G' o , temperature, ratio of product and reactant concentrations (Q): • G = G' o + RT ln Q • Enzymes only speed up thermodynamically favorable reactions (having a negative G) !
AG"o is related to the equilibrium constant (the prime again indicates its biochemical transformation): at equilibrium, 4G=0, Q=K thus AGo--RTIn Ke The G and Go values are additive when reactions are coupled (1. e, sharing common intermediates), thus a thermodynamically unfavorable reaction can be driven by a favorable one The overall K ea is multiplicative(the product of wo,两值相乘), although AG o is additive (the algebraic sum of two 两值相如)
• G' o is related to the equilibrium constant K' eq (the prime again indicates its biochemical transformation): at equilibrium, G = 0, Q = K` eq , thus • G' o = -RT ln K' eq • The G and G' o values are additive when reactions are coupled (i.e., sharing common intermediates), thus a thermodynamically unfavorable reaction can be driven by a favorable one. • The overall K` eq is multiplicative (the product of two,两值相乘), although G' o is additive (the algebraic sum of two，两值相加)
4. ATP is the universal currency for biologiealenergy This was first perceived by Fritz Lipmann and Herman Kalckar in 194 1 when studying glycolysis Hydrolysis of the two phosphoanhydride(磷酸酐鍵 bonds in atp generate more stable products releasing large amount of free energy (4G is.5 kJ/mol: 4G in cells is-50 to -65 kJ/mol) The ATP molecule is kinetically stable at pH 7 (i.e it has a high activation energy, 4G* for hydrolysis) and enzyme catalysis is needed for its hydrolysis
4. ATP is the universal currency for biological energy • This was first perceived by Fritz Lipmann and Herman Kalckar in 1941 when studying glycolysis. • Hydrolysis of the two phosphoanhydride (磷酸酐键) bonds in ATP generate more stable products releasing large amount of free energy (G' o is -30.5 kJ/mol; G in cells is -50 to -65 kJ/mol). • The ATP molecule is kinetically stable at pH 7 (i.e., it has a high activation energy, G‡ for hydrolysis) and enzyme catalysis is needed for its hydrolysis
atP is not a long-term storage form of free energy in living cells, being consumed within a minute following its formation (phosphocreatine 磷酸肌酸, act as a energy storage form for longer term) A resting human consumes about 40 kg of ATP in 24 hours A provides energy by group transfer (donating ap PP or AMP to form covalent intermediates), not by simple hydrolysis atp has an intermediate A, thus ADP can accept and ATP can donate phosphoryl groups
• ATP is not a long-term storage form of free energy in living cells, being consumed within a minute following its formation (phosphocreatine, 磷酸肌酸, act as a energy storage form for longer term). • A resting human consumes about 40 kg of ATP in 24 hours! • ATP provides energy by group transfer (donating a Pi , PPi or AMP to form covalent intermediates), not by simple hydrolysis. • ATP has an intermediate phosphoryl group transfer potential, thus ADP can accept and ATP can donate phosphoryl groups