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  #1  
Old 08-22-2011
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Biochemistry Enzyme kinetics Q

the reaction catalyzed by hepatic phosphofructokinase-1 has a G0 value of -3.5 kcal/mol. this value indicates that under standard conditions this reaction.

a. is reversible
b. occurs very slowly
c.produces an activator of pyruvate kinase
d. inhibited by ATP
e. will decrease in activity as the ph decreases
g. cannot be used for gluconeogensis
h. shows cooperative substrate binding
i. is indirectly inhibited by glucagon
j. is stimulated by fructose 2,6 bisphosphate

plz with explanation
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Old 08-22-2011
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Default C

C- produces an activator of pyruvate kinase
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Originally Posted by menatallah Elgohary View Post
the reaction catalyzed by hepatic phosphofructokinase-1 has a G0 value of -3.5 kcal/mol. this value indicates that under standard conditions this reaction.

a. is reversible
b. occurs very slowly
c.produces an activator of pyruvate kinase
d. inhibited by ATP
e. will decrease in activity as the ph decreases
g. cannot be used for gluconeogensis
h. shows cooperative substrate binding
i. is indirectly inhibited by glucagon
j. is stimulated by fructose 2,6 bisphosphate

plz with explanation
Under standard conditions the net deltaG is negative (used ATP) = is irreversible! = G) cannot be used for gluconeogensis

Delta G0...sorry, not Delta G

Last edited by bebix; 08-22-2011 at 09:04 AM. Reason: typo
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Originally Posted by bebix View Post
Under standard conditions the net deltaG is negative (used ATP) = is irreversible! = G) cannot be used for gluconeogensis
u are right but can u explain it more to me as i cannot get it please why in delta G if -ve is irreversible and how that do with that it be used with gluconeogensis .. sorry but i really doesn't understande that part at all and thanks for your help
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Originally Posted by menatallah Elgohary View Post
u are right but can u explain it more to me as i cannot get it please why in delta G if -ve is irreversible and how that do with that it be used with gluconeogensis .. sorry but i really doesn't understande that part at all and thanks for your help
Delta G0 = standard change of reaction in Gibbs free energy

Delta G0 = G product - G reactants

Please read here under "The "Driving Force" of a Chemical Reaction"
http://www.chem.arizona.edu/~salzman...t/g&react.html
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  #6  
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Originally Posted by bebix View Post
Delta G0 = standard change of reaction in Gibbs free energy

Delta G0 = G product - G reactants

Please read here under "The "Driving Force" of a Chemical Reaction"
http://www.chem.arizona.edu/~salzman...t/g&react.html

isnt it that when deltaG < 0 ---> reaction is spontaneous ---> PFK! will form F1,6bisphosphate.. ...
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Originally Posted by drnirajmavani View Post
isnt it that when deltaG < 0 ---> reaction is spontaneous ---> PFK! will form F1,6bisphosphate.. ...
this is not delta G
this is delta G0

So, from F 6 P to F1,6 BP
the reaction will go in that direction, but will need ATP...is not reversible.

Last edited by bebix; 08-22-2011 at 09:08 AM. Reason: added info
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  #8  
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Correct Answer

Let us go step wise
A.Incorrect since G is negative The reaction is Irreversible

B.Incorrect since G is negative the reaction occurs spontaneously

C.Correct PFK-1 produces an Fruc 1,6 Biphosphate which is an activator of Pyruvate Kinase (Feed Forward feedback)

D. Correct this reaction has G negative so it releases energy hence increased ATP will lead to inhibition of this Step.
It can be seen in such a way :
When body has excess energy why will it need Glycolysis for energy generation

E. I am not sure about this

G. Correct since the reaction is irreversible,Gluconeogenesis can not occur.

H.Correct In Glycolysis PFK-2 produces Fruc. 2,6 Bisphosphate which will lead to activation PFK-1 hence leading to phenomenon of Co-operative substrate binding.

I. Correct Glucagon will lead to Indirect inhibition as it inhibits F 2,6 Bis P which is an activator of PFK-1

J. Correct.Its a Fact


Correct me if am wrong
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  #9  
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Originally Posted by bebix View Post
this is not delta G
this is delta G0

So, from F 6 P to F1,6 BP
the reaction will go in that direction, but will need ATP...is not reversible.

hey...jst correct wer m goin wrong...
deltaG is the energy involved in a reaction (not under std conditions)
deltaG0 is the energy involved in a reaction which is at a stndard state
now evn acc to ur link it says if deltaG0 < 0, reaction will go as it is written i.e.it will be spontaneous ,right?? so wer m i goin wrong, nd wers dis irreversible thing came in frm??
thanx in advance
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Originally Posted by drnirajmavani View Post
hey...jst correct wer m goin wrong...
deltaG is the energy involved in a reaction (not under std conditions)
deltaG0 is the energy involved in a reaction which is at a stndard state
now evn acc to ur link it says if deltaG0 < 0, reaction will go as it is written i.e.it will be spontaneous ,right?? so wer m i goin wrong, nd wers dis irreversible thing came in frm??
thanx in advance
yup, the reaction will go spontaneous in order to form F1,6B...
the delta G0 for this particular enzyme just let you go from F6P to F1,6bP...
G0 < 0 = you cannot go back.

so, if you need to go now from F1,6bP to F6P, you must use another enzyme.
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  #11  
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Originally Posted by usmle2011 View Post
Let us go step wise
A.Incorrect since G is negative The reaction is Irreversible

B.Incorrect since G is negative the reaction occurs spontaneously

C.Correct PFK-1 produces an Fruc 1,6 Biphosphate which is an activator of Pyruvate Kinase (Feed Forward feedback)

D. Correct this reaction has G negative so it releases energy hence increased ATP will lead to inhibition of this Step.
It can be seen in such a way :
When body has excess energy why will it need Glycolysis for energy generation

E. I am not sure about this

G. Correct since the reaction is irreversible,Gluconeogenesis can not occur.

H.Correct In Glycolysis PFK-2 produces Fruc. 2,6 Bisphosphate which will lead to activation PFK-1 hence leading to phenomenon of Co-operative substrate binding.

I. Correct Glucagon will lead to Indirect inhibition as it inhibits F 2,6 Bis P which is an activator of PFK-1

J. Correct.Its a Fact


Correct me if am wrong
Remember they are asking what you could conclude using JUST the G0 value.
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Originally Posted by bebix View Post
Remember they are asking what you could conclude using JUST the G0 value.
Lolz.. If I was in the exam with so less time I would have submitted C as the answer,being the first correct choice.

btw what about option E ...going out of the question.
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Lolz.. If I was in the exam with so less time I would have submitted C as the answer,being the first correct choice.

btw what about option E ...going out of the question.
I only know that exits an optimal pH for each enzyme catalyzed reaction.
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  #14  
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Yes that may be the case.
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Originally Posted by bebix View Post
this is not delta G
this is delta G0

So, from F 6 P to F1,6 BP
the reaction will go in that direction, but will need ATP...is not reversible.
thanks so much for your help but i think to have to work on it as i really don't know what this Gibbs free energy is i don't even remeber that i had studied it in collage .. i will try to understand more about it but thanks that u put me on the right tract ,, thanks
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Originally Posted by menatallah Elgohary View Post
thanks so much for your help but i think to have to work on it as i really don't know what this Gibbs free energy is i don't even remeber that i had studied it in collage .. i will try to understand more about it but thanks that u put me on the right tract ,, thanks
check Kaplan! (biochemistry chapter 8 I think)
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Originally Posted by bebix View Post
check Kaplan! (biochemistry chapter 8 I think)
yes u are right it's chapter 8 but unforuntaly i didn't understand it from it , i looking every where to try to understand it , i don't know what make it so hard on me ! but i will try again ,, thanks for help and advice hope i didn't bother u with too much asking
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So i guess answer is cannot be used for gluconeogensis, ..G. Due the reaction is irreversible so it cant not go another reaction.
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Old 08-23-2011
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Quote:
Originally Posted by bebix View Post
Under standard conditions the net deltaG is negative (used ATP) = is irreversible! = G) cannot be used for gluconeogensis

Delta G0...sorry, not Delta G
When delta G is negative. the reaction is spontaneous and irreversible and the energy is released not used!!
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Quote:
Originally Posted by menatallah Elgohary View Post
the reaction catalyzed by hepatic phosphofructokinase-1 has a G0 value of -3.5 kcal/mol. this value indicates that under standard conditions this reaction.

a. is reversible
b. occurs very slowly
c.produces an activator of pyruvate kinase
d. inhibited by ATP
e. will decrease in activity as the ph decreases
g. cannot be used for gluconeogensis
h. shows cooperative substrate binding
i. is indirectly inhibited by glucagon
j. is stimulated by fructose 2,6 bisphosphate

plz with explanation
I think so that for this -G value, under standard conditions the reaction should occur very slowly!!
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Old 08-23-2011
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Cant it be D?..
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Old 08-23-2011
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Quote:
Originally Posted by dr.aysa View Post
When delta G is negative. the reaction is spontaneous and irreversible and the energy is released not used!!
in this particular case you are using ATP! (going from F6P to F1,6P)
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