9: Energetics of Key Metabolic Steps Flashcards
Know how to use the 4 equations listed under “8. Summary” p. 177
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ΔG = 2 equations
AN OBJECTIVE
Focus on Free energy
-nFΔE = ΔG°’ + (1.36)log(products/substrates)
Notes:
Free energy:
When you reverse the direction for writing a reaction, you change the sign of the standard free energy change. This holds also for ΔG.
biochemists define their standard states as ∆G°’. ΔG = ΔG°’, when (subst) and (prod) = 1 M, except H2O = 55.5 M and H+ = 10-7 M.
For sequential reactions the overall ΔG°’T is equal to the sum of the ΔG°’ for each step. This relationship also holds for calculating ΔGT from ΔG for each step.
ΔG°’ =
AN OBJECTIVE
(-1.36)log K’eq
ΔE =
AN OBJECTIVE
ΔE°’ + (.059/n)log(substrates/products)
Note that this one is reversed!
Define entropy & free energy:
ΔS: Entropy, increase (+) or decrease (-) in the randomness of the system. Can be + or – for a spontaneous reaction as long as the entropy of the universe increases.
ΔG: Free energy, the maximum amount of energy which could theoretically be used to do work. Always negative for a spontaneous reaction.
If ΔG is negative, the reaction can proceed from left to right (exergonic).
If ΔG is positive, the reaction will not proceed from left to right (endergonic). In fact, it will proceed from right to left.
If ΔG is zero, there is no net reaction in either direction. The reaction is at equilibrium.
What is a Biochemical standard state?
[H2O] = 55.5 M
[H+] = 10^-7 M
ΔG = 2 equations
AN OBJECTIVE
Focus on Redox
-nFΔE = ΔG°’ + (1.36)log(products/substrates)
Notes:
Redox:
ΔE°’ + (.059/n)log(substrates/products)
RULE: The more positive the standard reduction potential the greater the affinity of the e- acceptor for the electron.
if e-‘s tend to flow to the right, the E° is positive (+). If e-‘s tend to flow to the left, E° is negative (-).
The minus sign accounts for the fact that you are reversing the direction of one of the reactions to make it an oxidation. Don’t change the sign twice.
n is the number of electrons transferred, F = 23.063 kcal/(mol•volt), ΔE°” must be expressed in units of volts.
Log (0) =
Log (1) =
Log (10) =
Log (1/10) =
Log (100) =
Log (10^-2 * 10^-3) =
Log (10^-2 / 10^-4) =
Log (0) = infinite
Log (1) = 0
Log (10) = 1
Log (1/10) = -1
Log (100) = 2
Log (10^-2 * 10^-3) = -5
Log (10^-2 / 10^-4) = 2
Questions will only be power of 10’s on exams
Info given on tests
RT*ln(x) = (1.3)log(x)
RT/nF*ln(x) = (.059/n)log(x)
Faraday constant, F = 23 kcal/(mol•volt)
