Class8_glycolysiskinetics.pptx - For, after all, how do we...

“For, after all, how do we know that two and two make four? Or that the
force of gravity works? Or that the past is unchangeable? If both the past
and the external world exist only in the mind, and if the mind itself is
controllable – what then?”
- George Orwell, 1984
“Any technological advance can be dangerous. Fire was dangerous from
the start, and so (even more so) was speech - and both are still
dangerous to this day - but human beings would not be human without
them.”
― Isaac Asimov

Announcements

The reaction quotient Q, gives the current
state of the products and reactants
•
For the reaction A+B ↔ C+D,
Q=[C][D]/[A][B] is the
reaction quotient.
•
The instantaneous Gibbs energy for a reaction is
given by Δ G = Δ G° + RT ln Q or 1.4 log Q
•
If Q < Keq : The reaction will shift to the right (i.e. Δ G<0, reaction
goes in the forward direction, and thus more products will form)
•
If Q > K eq: The reaction will shift to the left (i.e. Δ G>0, reaction goes
in the reverse direction, and thus more reactants will form)
•
If Q = Keq : The reaction is at equilibrium (Δ G=0)
Zumdahl, Steven; Zumdahl, Susan (2003). Chemistry 6th Edition .
Houghton Mifflin Company. ISBN 0-618-22158-1 .

Clicker question: For the reaction A+B ↔ C+D, if  G is
positive, how would the products or reactants have to
change Q to make  G negative?
G
G

Energetically unfavorable reactions are enabled by
coupling them with favorable reactions
•
Example: Glutamic acid + NH3 ↔ glutamine, ΔG°’ = +3.4 kcal/mol
•
Recall that ΔG°’ for ATP hydrolysis = -7.3 kcal/mol
•
First, a
reaction intermediate
is formed in the reaction
Glutamic acid + ATP ↔ glutamyl phosphate + ADP
•
Second, it is energetically favorable for the reaction intermediate to
proceed to replace its phosphate with an amine group (NH3) in the
reaction Glutamyl phosphate ↔ glutamine + Pi
•
Total reaction is glutamic acid + ATP + NH3 ↔ glutamine + ADP + Pi

The difference in ΔG°, not the absolute value of
ΔG°, will determine the ΔG of a coupled reaction
•
Anything higher on the
chart, (larger ΔG°), can
drive the reverse
reaction of anything
lower on the chart
•
For example, hydrolysis
of phosphoenolpyruvate
can drive ATP synthesis,
and ATP hydrolysis can
drive phosphorylation of
glucose

Clicker question. Based on the chart, what is the
approximate  G°’ for the reaction Glucose -->