Download Lecture 16: Thermodynamics and Biochemical Energetics in Biochemistry 440, Fall 2008 - Pro and more Study notes Biochemistry in PDF only on Docsity!
Lecture 16 1
Thermodynamics &
Biochemical energetics
Thermodynamics
- Free energy change of a reaction (ΔG)
- Standard free energy change (ΔGo)
- Relationship of ΔG and ΔGo Bioenergetics
- Coupling of reactions
- ATP Reading assignment: Chapter 13.1 & 13. box 13-1 optional; 13.2 for review only Lecture 16 2
ΔG - the change in free energy
Lecture 16 3
What is ΔG?
ΔG is the change in free energy. Consider the reaction A + B <--> C + D -> Initial conditions: Ai + Bi <--> Ci +Di -> At equilibrium: Ae + Be <--> Ce + De Lecture 16 4
What is ΔG?
! G = RT ln
[ C i ][ D i ]
[^ Ai ][ Bi ]
" RT ln
[ C e ][ De ]
[^ Ae ][ B e ]
Equation 1: Equation 2:
! G = RT ln
[ C i ][ Di ]
[^ Ai ][ Bi ]
" RT ln Keq
R is the gas constant T is the temperature in degrees Kelvin
Lecture 16 5
ΔG^0 is the change in standard free energy.
At standard state, the concentrations of reactants and products are ΔG^0 is the change in free energy going from Substituting into Equation 2 gives Equation 3:
! Go^ = RT ln
" RT ln Keq
Lecture 16 6
ΔG^0 is the change in standard free energy.
Solving Equation 3 gives: Equation 4: 2.303 RT is approx 5 kJ/mole at 25˚C.
! Go^ = " RT ln Keq
! Go^ = "2.303 RT log Keq
In biology, we use ΔG’^0. Standard state with additional assumptions pH = 7. 55 M H 2 O 1mM Mg2+ K’eq makes the same assumptions. Lecture 16 7 Change to log base 10 to give Equation 6:
The relationship of ΔG to ΔG’^0.
Substituting equation 4 into equation 2 gives: Equation 5: ! G =! G '^0 + RT ln
[ C i ][ Di ]
[^ Ai ][ Bi ]
! G =! G
' 0
+ 2.3 RT log
[ C i ][ Di ]
[^ Ai ][ Bi ]
ΔG > 0 =>
ΔG < 0 =>
Lecture 16 8
Consider the reaction A <--> B
Given the reaction A <--> B If [A] = 0.1 M and [B] = 1 M And K’eq = 100 What is Q? What is ΔG’^0? What is ΔG? In which direction will the reaction proceed?
Lecture 16 13 ATP-coupled reactions ΔG’o^ [kJ/mol] ATP+H 2 O <-> Pi+ ADP -30. Pi+Glucose<->Glucose-6P+H 2 O +13.
ATP+Glucose<->Glucose-6P+ADP -16. Lecture 16 14 ATP-coupled reactions in vivo : Direct coupling by an enzyme ATP + Glucose <--> ADP + Glucose-6P Direct phosphoryl-group transfer, no Pi intermediate, bond energy preserved Lecture 16 15 ATP is the most widely used energy currency of the cell P - P - adenosine P - adenosine Lecture 16 16 ATP-hydrolysis Hydrolysis ATP + H 2 O --> ADP + Pi ΔG’^0 = -30.5 kJ/mol Phosphoryl group has high transfer potential Hydrolysis of ATP is favored because ATP is kinetically stable -> high activation energy for hydrolysis
Lecture 16 Figure 13-11^17 Lecture 16 18 ATP does not have the highest transfer potential ΔG’^0 Phosphoenolpyruvate -61.9 kJ/mol Creatine phosphate -43.0 kJ/mol ATP -30.5 kJ/mol Glucose 6-phosphate -13.8 kJ/mol Lecture 16 19 ATP provides energy by group transfers Figure 13-
