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Consider the following list of phosphorylated compounds with their free energies of phosphate hydrolysis:

a) Glucose-1-phosphate: -5.0 kcal/mol
b) PEP: -14.8 kcal/mole
c) ATP: -7.3 kcal/mol
Which of these molecules could phosphorylate an unknown compound whose free energy of phosphate hydrolysis is -10.3kcal/mol?
A) Glucose-1-phosphate only
B) PEP only
C) ATP only
D) ATP and PEP
E) All three could phosphorylate the unknown compound.

User Ali Mezal
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1 Answer

4 votes

Final answer:

In the context of phosphate group transfer, only molecules with a higher (more negative) free energy of hydrolysis can phosphorylate another compound. PEP and ATP both have sufficient energy to phosphorylate the unknown compound with a free energy of -10.3 kcal/mol, unlike Glucose-1-phosphate. Consequently, the molecules that could phosphorylate the unknown compound are PEP and ATP.

Step-by-step explanation:

To determine which molecules could phosphorylate an unknown compound with a free energy of phosphate hydrolysis of -10.3 kcal/mol, we compare the given free energies of hydrolysis for each molecule: Glucose-1-phosphate (-5.0 kcal/mol), PEP (-14.8 kcal/mol), and ATP (-7.3 kcal/mol under standard conditions and approximately -14 kcal/mol in cellular conditions).

In biochemical reactions, a compound can phosphorylate another if it has a greater (more negative) free energy of hydrolysis. Thus, we are looking for the compounds with the free energy of hydrolysis more negative than -10.3 kcal/mol. In this case, both PEP and ATP have sufficient energy (-14.8 kcal/mol and approximately -14 kcal/mol in cellular conditions, respectively) to phosphorylate the unknown compound, since their values are more negative than -10.3 kcal/mol. However, Glucose-1-phosphate does not have enough energy for phosphorylation because its free energy (-5.0 kcal/mol) is not as negative as that of the unknown compound.

Therefore, the correct answer is ATP and PEP, which translates to option D. These molecules have a higher phosphate transfer potential and can thus donate their phosphate group to the unknown compound.

User Hamed Jaliliani
by
8.5k points
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