amitdoc2b
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Hi!!
I wanted to thank everyone who has helped me out with the NBME questions for this topic. But I still have some questions that were are unanswered and my exam is in 2 weeks!  Can you please help me out with them? I wanted to understand also why it is the correct answer and I have been having trouble finding the reasoning behind these particular questions.
Thanks so much..ive attached the file below..
Attached Files:
biochem.JPG (23 KB, 112 downloads)
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| KOBITA
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Answer D) Y
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| AngelT
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Hi Kobita! Why? I didnt understand... ; (
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| amitdoc2b
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i dont understand also?
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| Musuq
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| Musuq
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| docarchana
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thanku for a great explanation musuq. u finally appear to have solved this ques which has been in the forum for months.
goodluck.
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| vanshita
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thank you
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| amitdoc2b
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Musuq wrote:
Suppose instead of +5.7 between Y and Z, it was +7.7 between them. Would the answer then be Y instead of W??
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| Musuq
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ok amitodc2b, now you got me 
Before it was easy cause W= -3.6 higher number and being spontaneous because the sign, that made everything very easy to conclude that this is gonna be accumulated but now with the 7.7???
now Y= +4.4 <<< and W= -3.6 >>>
but still W is an spontaneous reaccion and by itself would accumulate, but gosh the other number is bigger, damn it, you know what, just let me ask doctor Hansen ok cause I dont want to give you a wrong answer, thanks for the qs 
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| amitdoc2b
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Musuq wrote:ok amitodc2b, now you got me Before it was easy cause W= -3.6 higher number and being spontaneous because the sign, that made everything very easy to conclude that this is gonna be accumulated but now with the 7.7??? now Y= +4.4 <<< and W= -3.6 >>> but still W is an spontaneous reaccion and by itself would accumulate, but gosh the other number is bigger, damn it, you know what, just let me ask doctor Hansen ok cause I dont want to give you a wrong answer, thanks for the qs
Thanks Musuq for your help. Please find out soon because my exam is in 9 days! Who is Dr Hansen - is he a professor of urs?
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| Musuq
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gosh, ok, I will try to get this answer asap.
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| amitdoc2b
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Musuq wrote:
gosh, ok, I will try to get this answer asap.
hi..did u find out about the biochem delta G question.. my exam is thurs (31st). thanks..
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| tran6996
Forum Newbie
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My point of view from this question is different. I think the answer is V.
speaking of delta G
if Delta G is < 0 ==> spontaneous rxn will occur
if Delta G is > 0 ==> NO rxn
From the question above, you can eliminate out the +delta G b/c the reaction will NOT occur spontaneously.
Now, you have the 2 neg delta G left. The question ask which one occur more.
the further away from zero, the rxn will occur more. So the answer is V.
Any comments is welcome
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| ssrpk
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I will go with d) 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.
Edited by ssrpk on 08/28/06 - 04:52 PM
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| tran6996
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hey Dr, If you got PERFECT score NBME on biochem...then I guess there is no more discussion
the answer is D 
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| Musuq
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The explanation I gave some posts above was straight from Dr Hansen's explanation, she is member of the faculty at kaplan, at Biochem. I was very confused about this qs and she explained it to me just like I posted above.
Now, for the second supossition of amitdoc, if we follow the same path that Dr. Barbara Hansen, we would end with:
Y= + 4.4 <- No Rxn
W= - 3.6 -> Spontaneous Rxn
I would go with accumul of W for this personal qs of amitdoc but that is just my answer, need to ask some expert to be sure.
Edited by Musuq on 08/28/06 - 06:19 PM
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| ssrpk
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well buddy, heard alot abt dr.hansesn, it wud be best if u can ask her directly this very question as sometimes we make errors in interpretation!
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