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Vaishaalie_6729
#1 Posted : Thursday, July 08, 2021 4:57:13 AM
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Hello I have a question on glycolysis!

It is to my understanding than steps 1, 3 and 10 in glycolysis are irreversible, because they are exergonic processes. It is also to my understanding that catabolic reactions are exergonic. Catabolic reactions occur when you break one large molecule into two smaller ones, however, in step 3, we are adding a phosphate group (fructose-6-phosphate to fructose-1-6-biphosphate) - wouldn't this reaction be anabolic (as we are adding two molecules (fructose-6-phosphate + Pi) together to create a larger molecule). OR would it be catabolic (-ve free energy) because ATP is broken down into ADP + Pi. If this is the case, then shouldn't step 10 be anabolic (+ve free energy) as ATP is being made? I would love any clarification on this topic.
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INSTR_Molly_129
#2 Posted : Saturday, July 10, 2021 5:12:05 PM
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Hi Vaishaalie,

All steps in glycolysis requiring a kinase of some sort is an irreversible step. In general, catabolic reactions result in an exergonic reaction, but during the kinase step, there are two molecules at play. One is undergoing an anabolic reaction and the other is catabolic.

The breaking down of a phosphate group from ATP to ADP makes it catabolic, and results in a release of energy (exergonic).

The build up of the molecule from F6P to F1,6P is anabolic and results in absorption of energy (endergonic).

The difference in Gibbs free energy is the summation of the energy that is gained and lost. Overall, the entire reaction as a whole is an endergonic reaction.

Hope that clarifies this!

Cheers,

Molly
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