Can anyone explain deltaG stuff?

[GRAYANATOMY]

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. ΔG0'

V ↔ W ?4.0
W ↔ X +0.4
X ↔ Y ?3.4
Y ↔ Z +5.7

From the values of ΔG0' given in the table, which compound in the overall metabolic pathway V ↔ W ↔ X ↔ Y ↔ Z will accumulate in the largest amount at equilibrium?

A) V
B) W
C) X
D) Y
E) Z
please explain the ans

 

[killinsound]

I say Y... am i right?

 

[HippocratesX]

can you explain your reasoning killinsound? Also...at equilibrium, isn't the reaction at greatest entropy and with the least amount or no free energey (dG)? I thought i remember reading that somewhere.

 

[mc4435]

. ΔG0'

V ↔ W ?4.0
W ↔ X +0.4
X ↔ Y ?3.4
Y ↔ Z +5.7

From the values of ΔG0' given in the table, which compound in the overall metabolic pathway V ↔ W ↔ X ↔ Y ↔ Z will accumulate in the largest amount at equilibrium?

A) V
B) W
C) X
D) Y
E) Z
please explain the ans

It depends what the "?" is before 4.0 and 3.4. Negative or positive that changes everything.

 

[killinsound]

well it's most likely negative.

I actually think it's W now because

V -> W because the equil lies on the right side

W -> X ... keeping it simple, less than half W of it goes to X

X -> Y... most of it goes to Y

Y -> Z ... most of it stays at Y because of the unfavorable rxn.

This is assuming equilibrium where the kinetics don't really matter and we started out wiht just V

So if less than half of W goes to X, and X goes to Y, then W will be more than Y

 

[devlyyn]

Well it would seem like V will react to W and X will partially react to W and partially react to Y. For Y, all of Z will react to form Y and part of X will also react to form Y. That still seems to indicate that W and Y will be present in the same amount?

Unless you approach it that since V will go to form W but W will not spontaneously form X the reaction will stop at W and it will be formed in the most abundance. I'm not sure.

 

[CATallergy]

I vote for Y (how confident am I? - I would also mark aamc's "guess" box).

reason for Y vote:
If you draw an energy peak/trough diagram starting arbitrarily with 0 at V, then of -4 at W, -3.6 at X, -7 at Y, and -1.3 at Z, Y is definitely the deepest trough. to get to equilibrium, I generally assume that all activation energies for each step have been sufficient for spontaneous steps to occur.

I don't really understand killinsound's logic for estimating reaction fractions based on delta G, so maybe s/he can explain.

 

[killinsound]

I don't really understand killinsound's logic for estimating reaction fractions based on delta G, so maybe s/he can explain.

i knew someone was going to bring this up

what I was trying to say was that in the rxn W <-> X, it is very close in free energies, however there is a slight bias to W. Since there is a slight bias, no matter if X went to Y irreversibly, there would still be more W. (this is also assuming i completely forgot about the fact that it was in equlibrium)

i too would check guess

EDIT : with more thought, i agree with CATallergy... unless s/he is wrong, then i agree with myself again.

Anways here is my final logic.

Since W <-> X is so close, the X that is produced will go to Y. Y then has to overcome the highest gibbs free in either direction, so it will stay in Y. As X is converted into y, more W will be converted into X. so Y will have the most

 

[GRAYANATOMY]

Oh, it was typo
instead of question mark these two values have a negative sign.
i.e V to W
X to Y

 

[CATallergy]

i knew someone was going to bring this up

what I was trying to say was that in the rxn W <-> X, it is very close in free energies, however there is a slight bias to W. Since there is a slight bias, no matter if X went to Y irreversibly, there would still be more W.

i too would check guess

with more thought, i agree with CATallergy

ok, so the W-X is biased to W, but as X gets converted to Y, wouldn't that shift the W-X concentrations toward producing more X?

 

[CATallergy]

i knew someone was going to bring this up

what I was trying to say was that in the rxn W <-> X, it is very close in free energies, however there is a slight bias to W. Since there is a slight bias, no matter if X went to Y irreversibly, there would still be more W.

i too would check guess

EDIT : with more thought, i agree with CATallergy... unless s/he is wrong, then i agree with myself again.

CATallergy is a he. I knew a name containing the word "cat" might be a bad idea..

 

[killinsound]

ok, so the W-X is biased to W, but as X gets converted to Y, wouldn't that shift the W-X concentrations toward producing more X?

ah you replied before i finished my edit... please look again 🙂

 

[GRAYANATOMY]

Cat Allergy can you please send me a link where i can read this stuff my self basic G stuff basics .May be i am asking too much but any input will be helpful.I am not Mcat student .......but this is a board question. Thankyou.

 

[CATallergy]

Cat Allergy can you please send me a link where i can read this stuff my self basic G stuff basics .May be i am asking too much but any input will be helpful.I am not Mcat student .......but this is a board question. Thankyou.

I wish I could help you, but I don't know of any good place - if I were you, I would look in a general chemistry textbook.