pearljam59
Forum Guru
Topics: 120
Posts: 273
|
BIOCHEM RXNS
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
|
| pearljam59
Forum Guru
Topics: 120
Posts: 273
|
Usually I wait for some answers before I give my two cents. The rules are simple:
NEGATIVE delta G means the rxn will proceed spontaneously
POSITIVE delta G means the rxn will not proceed spontaneously
delta G of ZERO means the rxn is at equilibrium; = amounts of product and substrate
So I would initially say the answer is W because the rxn involving V ↔ W has the greatest NEGATIVE delta G meaning the rxn will proceed SPONTANEOUSLY at the fastest rate. However, all the rxns are WRITTEN in equilibrium ( ie ↔ ) AND also every rxn SHARES an intermediate so I think the PROPER way to go about answering this is by the addative effect of ALL the delta G's and crossing out the INTERMEDIATES. So the FINAL rxn will read:
V ↔ Z with a delta G of -1.3 so since it is negative it will proceed in a forward rxn resulting in an accumulation of Z.
Sooooo any thoughts?!
|
| robin082006
Forum Hero
Topics: 471
Posts: 5,125
|
Based your reasoning, how can you explain for reaction from V->Y, accumulating -4+0.4-3.4=-7
___________________
The Key to Succeed is Patience.
|
| pearljam59
Forum Guru
Topics: 120
Posts: 273
|
Because Y is an INTERMEDIATE of another rx in what is a SINGLE METABOLIC PROCESS OF RXNS. so you have to add delta G of the final rx Y to Z and then use that delta G to decide which way the rxn X to Z goes.
Make sense?!
|
| vamsi2004
Forum Elite
Topics: 7
Posts: 144
|
pls someone try to answer this q....
|
| coolmavs
Forum Elite
Topics: 21
Posts: 327
|
Bumpin this question......Any answers?
___________________
Yeh Zeher bhi, yoon piya hai.....Jaise sharaab ho!!!!
|
| girl^interrupted
Forum Elite
Topics: 68
Posts: 264
|
Ans: W
will xplain in a while...
___________________
If you plan too much ahead of time, You lose your focus.
|
| girl^interrupted
Forum Elite
Topics: 68
Posts: 264
|
Rules first:
If ΔG0' is -, then the reaction will move from A--->B
If ΔG0' is +,then the reaction will move from A<---B
Above person failed to write the minus signs.
Breaking reaction in 2 parts:
1)
V--->W -4.0 means W will accumulate ΔG0': -4.0+0.4= -3.6
W<---X +0.4 means W will accumulate
2)
X----->Y -3.4 " " Y " " ΔG0': -3.4+5.7= +2.3
Y<----Z +5.7 " " Y " "
Now , solving W<----->Y mystery: Since, for W we had -3.6, and for Y we had 2.3, the reaction will definitely go towards "W" and hence this will accumulate.
___________________
If you plan too much ahead of time, You lose your focus.
|
| Addicudo
Forum Guru
Topics: 124
Posts: 608
|
girl_interrupted .. !! ... Angelina Jolie .. !! hits RIGHT on target .. !! Very well explained .. !! Answer is Def (W) .... Looked it up in Biochem Illuss Lippincot .. !! 
___________________
... Idle hands are the DeVilS play ground ...
|
| DRFP
Forum Junior
Topics: 7
Posts: 101
|
Well it seems Dr. Hanson had a different idea answer Y
"-the delta G values have two components to it, one is a sign (+ / - ) and the other is magnitude!
-magnitude tells us about the energy difference between the reactant and product, while sign only tells the direction in which the reaction would proceed.
-therefore if in the given question 'W' is getting accumulated in the first two reactions by a factor 4G and 0.4 G, then all it means that overall W is accumulating by a cumulative thermodynamic factor of 4.4 [ the signs will not add here like + & - = - or - & - = + ; as its all about the direction in which we write our equation eg: W<->X = +0.4 is the same as writing X<->W= -0.4] i hope u get the point
-if we analyze W and Y above keeping in mind the direction of reactions (given by the signs), Y would accumulate the most as in the first reaction for Y, the energy difference is 3.4 favoring Y while in the second reaction the energy diff. is 5.7 again favoring Y, therefore a total of 9.1 G or energy difference that would favor accumulation of Y.
i think the answer has to be D,and i know this for a fact tht i got this q on my nbme and i got perfect scores in biochem on both of the nbme forms and i checked D at tht time (as nbme don't release answers).....you may wanna check out that reference again.
And do keep in mind one very important fact that every reaction is reversible, however reversibility of any reaction depends on the thermodynamic state of the reaction�..which means even a reaction with a positive G can be made to proceed in the direction of product if enough energy is provided, but if the reaction is left to come to an equilibrium without an external supply of energy it would do so and the direction would depend on the value and sign of G.
"
From a previous post so I would think that since the reaction is going both ways then the accumulation of energy is greatest in Y too
___________________
Yea how I feel studying for this test!
|
|
| |
| | | | | | | | | | |
