Transcript Document

Monday Sept. 5
(it’s supposed to be a
national holiday)
Free Energy from Chemical
Reactions
aA bBcC dD
We can write a description of this reaction at any moment in time
as the mass-action ratio (q)
c
d
[C] *[D]
q
[A]a *[B]b
At equilibrium we say that:
c
Continued
d
[C] *[D]
q  K eq 
[A]a *[B]b
Since, by definition, a system at equilibrium can do no work, then
any system displaced from equilibrium can do work in either the
forward or reverse direction (depending on the direction of
displacement from equilibrium.)
Thus:
K
GC   nRT ln
q
or:
K
GC  2.3* nRT log
q
Chemical Free Energy Plot
Absolute Value of G
ATP Free Energy Problem
[ADP][Pi ] 0.001* 0.010
q

 0.0033
[ATP]
0.003
K
230,125
G  nRT ln( )  0.00831* 298 * ln(
)
q
0.0033
G  2.48 *18.1
G  44.7kJ*mol-1
Another Round of Review
Questions
1. Why do cells maintain concentrations of the
members of the ATP system so far from equilibrium?
2. What does being an open system have to do with your
answer to question(#1?
3. Can individual reactions in an otherwise open,
dynamic system come to Keq?
Metabolism -- ~P Homeostasis
The Ce ntral Role of ATP in Ce llular Ene rge tics
Storage Compounds
(Carbohy drates, Fats)
Catabolic
Pathways
(Breakdown of Complex
Molecules, Aerobic and
Anaerobic ~P
production)
(SUPPLY)
(Spontane ous)
Complex Molecules(poteins, lipids, complex carbs,
protein complexes
OR
Movement and transportrelated processes requiring
enery such as muscle contraction and activ e transport)
ATP
ADP + Pi
Anabolic
Pathways
and
Movement
(DEM AND)
(NonSpontane ous )
knp
Waste Products
(Mainly CO2
and Water)
Raw Materials (Amino Acids,Simple Carbs, etc; also
protein conf ormationsin the case of mov ement
The Measurement of
Metabolism
We will not directly follow these processes any more
than a chemist does who measures the heat evolved or
taken in by a process.
Methods all involve assumptions -- in a way it is like
measuring the economy and no one measure is perfect.
Phosphagen Cycle -Phosphagen Buffer During
High Demand
creatine kinase
C~P + ADP ----------------------> ATP + Creatine
demand reactions
Pi + ADP <----------------------- ATP
This process is controlled by the amount of enzyme
present (CK) and thermodynamically (amts. of
reactants/products)
Replenishment of
Phosphagen
creatine kinase
Creatine + ATP ----------------------> C~P + ADP
aerobic metabolism
ATP <----------------------- Pi + ADP