1. ATP and Energetics of Metabolism
C483 Spring 2013

2. 1. What is false of a near-equilibrium reaction?
A) Concentrations of reactants and products are near equilibrium concentrations.
B) The enzyme reaction is most likely not regulated
C) The standard free energy of the reaction is near zero.
D) The free energy of the reaction is near zero.
2. Which thermodynamic quantity is used to determine if a reaction in a cell is spontaneous?
A) △G°'
B) △G
C) △H
D) △S
3. The hydrolysis of ATP to ADP has a △G°' of -30 kJ/mol. If in an E. coli cell the concentrations of ATP, ADP and inorganic phosphate are 7.90 mM, 1.04 mM and 7.9 mM, respectively, which statement is true about the hydrolysis of ATP in the cell?
A) Hydrolysis cannot proceed spontaneously.
B) The hydrolysis is at equilibrium.
C) The free energy of the reaction is less negative than the standard free energy.
D) The free energy of the reaction is more negative than the standard free energy.
E. More than one of the above are true.

3. 4. Which of the following is not a factor contributing to the large free energy of hydrolysis of ATP?
A) Electrostatic repulsion of oxygen atoms.
B) Better solvation of products than ATP itself.
C) Complexes with Mg2+ or Mn2+ ions.
D) Better stability of products than ATP itself.
E) Electrical shielding of products of hydrolysis.
5. ATP is thermodynamically suited as a carrier of phosphoryl groups in animal cells because
A) it is stable under cell conditions.
B) it is not hydrolyzed in cells without enzyme action.
C) it is intermediate in group-transfer potential.
D) All of the above.

4. Catabolism

5. Anabolism

6. ATP Hydrolysis High energy bonds—inherent chemistry
Electrostatic repulsion
Solvation of products
Resonance
Rxn goes to “completion”

7. Qualitative Predictions
Inherently favorable, unfavorable, or near equilibrium?

8. Energetics: A metaphor

9. Standard Free Energy vs. Free Energy
DGo’ is negative
DG is negative
DGo’ is negative
DG is zero

10. Standard Free Energy vs. Free EnergyAD
DGo’ is -32 kJ
DG is -32 kJ
ATP
ADP + P
ADP P
DGo’ is -32 kJ
DG is zero
ATP

11. Quantitative
Inherent component
Concentration component

12. Equilibrium Equilibrium = DEAD!
What is [product]/[rxt] equilibrium of ATP hydrolysis to ADP?
[ADP][Pi]/[ATP] = 4.1 x 105

13. Free Energy of ATP hydrolysis
Actual cellular concentrations don’t vary much from [Pi]=[ATP] = 5 mmol and [ADP]= 1 mmol
What is the actual free energy of ATP hydrolysis in the cell? More or less than -32 kJ?

14. Two Types of Reactions Near-equilibrium reactions
[pdt] and [rxt] near equilibrium concentrations
DG close to zero (regardless of DGo’ )
Not regulated—part of overall flux of metabolism
Metabolically irreversible reactions
DG far from zero
Can only be overcome by energy input
regulated

15. ATP in Metabolism Overcoming a barrier
Can’t change concentrations (ammonia is toxic!)
Couple the reaction to a spontaneous reaction!
Write an equation to couple to ATP hydrolysis:

16. Mechanism of Coupling

17. Phosphoryl Transfer in Energetic Intermediates
Phosphoryl group transfer potential

18. Answers C B D