Q.49 Phosphoryl transfer reactions are essential for the energy content of a cell.
Find the correct answer in which the following phosphorylated molecules have
been arranged in a decreasing order of their phosphoryl transfer potentials:

A. Adenosine triphosphate
B. 1,3-bisphosphate glycerate
C. Phosphoenol pyruvate
D. Glucose-6-phosphate
E. Glucose-3-phosphate

Choose the correct answer from the options given below:

1. C, B, A, D, E
2. B, C, A, D, E
3. B, C, D, A, E
4. C, B, D, A, E

   Phosphoryl transfer potential measures a phosphorylated molecule’s ability to donate its phosphate group, ranked by the standard free energy of hydrolysis (ΔG°’), with more negative values indicating higher potential.

   Correct Answer

   The correct option is C, B, A, D, E (Phosphoenol pyruvate > 1,3-bisphosphoglycerate > Adenosine triphosphate > Glucose-6-phosphate > Glucose-3-phosphate).

   Molecule Explanations

   Phosphoryl transfer potential decreases as the phosphate group’s stability after hydrolysis increases or resonance/electrostatic factors weaken the bond.

   • C. Phosphoenol pyruvate (PEP): Highest potential (ΔG°’ ≈ -61.9 kJ/mol). The enol form tautomerizes to stable keto-pyruvate, trapping energy.​

   • B. 1,3-bisphosphoglycerate: High potential (ΔG°’ ≈ -49.4 kJ/mol). Acyl phosphate linkage allows direct phosphoryl transfer to ADP in glycolysis.​

   • A. Adenosine triphosphate (ATP): Standard reference (ΔG°’ ≈ -30.5 kJ/mol). Accepts phosphate from higher-potential donors like PEP.​

   • D. Glucose-6-phosphate: Low potential (ΔG°’ ≈ -13.8 kJ/mol). Simple alkyl phosphate; hydrolysis yields stable products with little energy release.​

   • E. Glucose-3-phosphate: Lowest (ΔG°’ ≈ -9 to -12 kJ/mol, similar or slightly below G6P). Primary alcohol phosphate; even less strained than G6P.​

   Introduction to Phosphoryl Transfer Potential Order

   In cellular metabolism, the phosphoryl transfer potential order ranks phosphorylated compounds by their ability to donate phosphate groups, crucial for energy transfer in glycolysis and ATP synthesis. This phosphoryl transfer potential order—starting with phosphoenolpyruvate (PEP), 1,3-bisphosphoglycerate, ATP, glucose-6-phosphate, and glucose-3-phosphate—guides reactions like substrate-level phosphorylation.

   Why Phosphoryl Transfer Potential Matters

   Higher-potential molecules donate phosphate to lower ones, driving ATP production. PEP and 1,3-bisphosphoglycerate power glycolysis steps, while glucose phosphates serve anabolic roles.​

   Detailed Ranking Breakdown

   Molecule	ΔG°’ (kJ/mol)	Key Reason for Potential
   Phosphoenol pyruvate (C)	-61.9	Tautomerization to pyruvate stabilizes. ​
   1,3-Bisphosphoglycerate (B)	-49.4	Mixed anhydride-like acyl phosphate. ​
   ATP (A)	-30.5	Resonance-stabilized ADP product. ​
   Glucose-6-phosphate (D)	-13.8	Alkyl ester; low hydrolysis energy. ​
   Glucose-3-phosphate (E)	~ -10	Primary phosphate; least reactive. ​

   Glycolysis Context

   In glycolysis, GAPDH forms high-potential 1,3-bisphosphoglycerate, which PGK uses to phosphorylate ADP. Later, enolase produces PEP for final ATP via PK.

   Exam Tips for Life Sciences

   For GATE or similar exams, memorize: PEP > 1,3-BPG > ATP > sugar phosphates. Options like C, B, A, D, E test this exact sequence.​