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Bioenergetics and Oxidation of Fuels: Overview


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Is a rxn that gives off heat spontaneous or nonspontaneous?
Can a rxn that obsorbs heat be spontaneous?
What must the Gibbs free energy sign be to be spontaneous?
Negative -∆G
What is favorable, a postive or negative enthalpy change?

What is favorable, a positive or negative entropy change?

∆G= ? - ?
∆G = ∆H - T∆S
What does ∆H represent and which sign is favorable?
heat absorbed or released
negative is favorable
What does ∆S represent and which sign is favorable?
measure of disorder
positve is favorable
Which is thermodynamically favorable endergonic or exergonic?
If ∆G is zero and a system is at equilibrium, can a change take place?
Can a rxn occur spontaneously if the ∆G is positive
No, energy must be added
∆G Products - ∆G Reactants = ?
∆G of the rxn
Given that the ∆G of a rxn depends only on the change in free energy of the products minus the reactants, does one take into account the intermediates?
No, the mechanism is not important... just the start and end points
Does ∆G tell us anything about the rate of a rxn?
Since ∆G does not reveal the rate of a rxn, what does?
Concentration of reactants, products and the temperature
So, how does nature vary the rate of a rxn?
by varying the [product], [reactants]... NOT temperature
What is the molar concentration of reactants and products, heat and pH at standard conditions (∆G°)?
all of them are 1 moleK
T =298K
pH =7.0
Can a rxn be thermodynamically favored at standard condition and be disfavored at physiological conditions?
Yes and vice versa
∆G = ∆G° + RT ln {([C][D])÷ (A][B])}, what is A and B and C and D, and which concentration will give you a thermodynamically favored rxn?
C and D = products
A and B = reactants
high concentrations of reactants (denominator) will give a favorable rxn.
if you start out with equal concentrations [reactant]= [product]and at equilibrium... then you end up with the following state the standard free energy: What is the ∆G?

a. [R]= [P]
b. [R]> [P]
c. [R]< [P]
a. [R]= [P] ∆G° = zero
b. [R]> [P] ∆G° = positive
c. [R]< [P] ∆G° = negative
A --> B + C ∆G = +5kcal/mol
B --> d ∆G = -8kcal/mol
A --> C + D ∆G = ? kcal/mol

1. Solve for the unkown.
2. How is this phenomenon exhibited in nature?
1. ∆G = -3kcal/mol
2. Nature couples unfavorable reactions with favorable ones to drive the unfavorable one.
What are the two ways nature manipulates the favorability of a rxn?
1. Change product and substrate concentrations
2. Couple a thermodyamically unfavorable rxn to a favorable rxn to drive the unfavorable rxn.
What is an example of coupling a thermodynamically unfavorable rxn to a favorable one?
Increasing [ATP]:[ADP] when ATP is in abundance (unfavorable) by using a proton gradient (favorable)
What is the free energy of the hydrolysis of ATP to ADP?
∆G = -7.3 kcal/mol
Why is it that the free energy of hydrolysis of ATP to ADP of as much as 12.7 Kcal/mol?
Because of the overwhelming concentration difference,where [ATP]10X >[ADP], thus a lot of energy is needed to force the formation of ATP, so when it hydrolyzed it all free a lot of energy.
Name 3 molecules, besides ATP, which have a high phosphoryl transfer potential (actually higher than ATP).
Creatine phosphate,
Why is the hydrolysis of ATP to ADP in the rxn of intracellular glucose (in the presence of ATP and Hexokinase) --> glucose-6-phosphate only -4 kcal/mol?
Because it's couple to a disfavorable rxn (phosphorylating glucose is disfavorable).
What effect does raising temperature have on a rxn?
It raises the temperature of the reactants and the products with respect to the transition state, thus the heat changes the energy associated with the reactant and product and now the transition state is now relatively lower.
How does nature lower the associated activation energy of a rxn?
How do heat and enzymes differ in speeding up a rxn?
heat changes the energy associated with reactants and products, while enzymes lowers the energy associated with the transitions state.
What does a niacin deficiency cause? and why?
Pelegra, which characterized by the 3Ds: dementia, dermatitis and diarrhea.

Why? Niacin is a precursor of NADH and NADPH.
How do NAD+ and FAD get their 2 electrons? (reduced)
The get them from the oxidation of molecules
1) What is reduction potential a measure of?

2) In reduction potential, E, which is favorable positive or negative?
1) Reduction potential is a measure of how much energy is released when a compound accepts an electron.

2) a positive reduction potential (+E) is favorable
If a substance gives up electrons to H+, would the reduction potential be negative or positive?
It would be negative
If a substance has a lower affinity for electrons than H+, what would sign of the reduction potential be?
For reduction potentials, which is favored positive or negative?
when summing up the reduction potentials, which do we reverse?
The substance more likely to be oxidized... or the one with the lower electron affinity = more negative reduction potential.
What is the relationship between free energy (∆G°') and reduction potential (∆E' sub zero)
They are proportional
Where are you more likely to find NADH and NADPH
NADH in catabolic processes
NADPH in anabolic processes, e.g. synthesis of fatty acids.
What is Coenzyme A?
It is an activate carrier of an acyl groups, which can react with water by releasing lots of free energy
What happen when you add water to acetyl-CoA group
The Acetyl and CoA are hydrolyzed releasing free energy.
Besides a CoA, what is an example of an activated carrier?
ATP is an activated carrier of phosphoryl groups and pyrophosphoryl groups
Which phosphoryl group is hydrolyzed when ATP --> ADP?
the gamma (which is terminal) and the beta groups.
What is the intermediate donor of free energy in biological systems, and in doing so is the deciding factor in whether reactions go forward or not?
What can shift the equilibria of coupled reactions by a factor of 10^8?
Name 5 biologicially important carriers of electrons.
NAD, FAD, CoQ, various hemes, and various Fe-S complexes

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