awards MBE would not exist without metabolism as we know it.
Catabolic pathways Anabolic pathways
Fig 10-6 glycolysis
Detail of Fig 10-8
13-2
Unnumbered, page 292 The role of ATP in a coupled reaction.
G = Go' + RTlnQ
G (standard free energy change) is a measure of the equilibrium ratio of products to reactants.
o'
G = -RTlnKeq so: G = -RTlnKeq+ RTlnQ
o'
G = -RTlnKeq+ RTlnQ G = RT(lnQ lnKeq)
If Q is > Keq = Keq < Keq then G is > 0 (reverse reaction is favorable) = 0 (at equilibrium) < 0 (reaction favorable as written)
Living cells are not at equilibrium!
Concentrations of reactants and products are typically far from the equilibrium values (Q Keq). We must consider steady state concentrations of these species for the determination of G.
Key Concept: HOMEOSTASIS
Metabolic Homeostasis
Homeostasis = maintenance of steadystate concentrations of pathway intermediates within a NARROW range The homeostatic state is one of maximum thermodynamic efficiency Maintains balance of cellular functions that utilize common metabolic intermediates
Catabolic pathways Anabolic pathways
Homeostatic conditions
Metabolic Pathways
1) Irreversible (Goverall << 0), but REGULATED! 2) Catabolic and anabolic pathways utilize many common intermediates, but differ at regulatory steps where G<< 0 3) Committed steps are typically points of regulation (e.g., allosteric effects on enzyme activity)
Box Powering 9-B human muscles.
Unnumbered, page 294 (2) Phosphorylated compounds.
31
P NMR of
1 min of exercise
human muscle: Before exercise
i
ATP
phosphocreatine
P
19 min of exercise
10 min after exercise
In-class problem
If creatine phosphate = 5 mM; ATP = 3 mM; creatine = 0.4 mM; and ADP = 0.8 mM
'
What is G at 37 C and pH = 7.2 for:
phosphocreatine + ADP + H+ G creatine + ATP
During study of pathways pay attention to:
1) Changes in structures of intermediates (esp. in carbon skeleton and in oxidation states of C atoms). 2) Phosphate group transfer. 3) Electron transfer (to/from NAD+/NADH etc.)
Least oxidized
Most oxidized
Reduced substrates Oxidized cofactors
Oxidized substrates Reduced cofactors
See Fig 10.6
Figure 9.09 The nicotinamide cofactors.
Unnumbered, page 285 (1) Nicotinamide cofactor.
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Two basic strategies ...