Q41. The high energy compound(s) is/are:
(A) Phosphoenol pyruvate
(B) Adenosine monophosphate
(C) 1,3–Bisphosphoglycerate
(D) Vitamin K
Phosphoenol pyruvate and 1,3-bisphosphoglycerate qualify as high-energy compounds due to their high negative standard free energy of hydrolysis (ΔG°’ ≤ -7.3 kcal/mol or -30.5 kJ/mol), enabling energy transfer in metabolic pathways like glycolysis. Adenosine monophosphate and vitamin K do not meet this criterion.
Option Analysis
Phosphoenol pyruvate (A): This enol phosphate features a high-energy phospho-enol bond with ΔG°’ of hydrolysis around -61.9 kJ/mol, the most negative among biochemical phosphates. In glycolysis step 10, pyruvate kinase transfers its phosphate to ADP, forming ATP (-31.7 kJ/mol released).
Adenosine monophosphate (B): AMP contains a low-energy ester bond between ribose and the phosphate (ΔG°’ ≈ -9 to -14 kJ/mol), far below high-energy thresholds. It signals low energy via AMPK activation but does not donate energy directly.
1,3-Bisphosphoglycerate (C): This acyl phosphate has a mixed anhydride bond at C-1 with ΔG°’ ≈ -49 kJ/mol, driving substrate-level phosphorylation in glycolysis step 7 via phosphoglycerate kinase.
Vitamin K (D): This fat-soluble vitamin supports carboxylation in coagulation factors via its quinone-hydroquinone cycle but lacks high-energy bonds for hydrolysis-based energy release.
Correct answers: (A) and (C).
High energy compounds serve as the cell’s energy currency, releasing ≥7.3 kcal/mol (30.5 kJ/mol) upon hydrolysis of bonds like phosphoanhydrides or enol phosphates. In glycolysis, they enable ATP production without oxidative phosphorylation.
Key Types
-
Enol phosphates: Phosphoenol pyruvate (PEP) tops with ΔG°’ -61.9 kJ/mol due to tautomerization to pyruvate post-hydrolysis.
-
Acyl phosphates: 1,3-Bisphosphoglycerate (1,3-BPG) at -49 kJ/mol from its C1 anhydride.
-
Others: ATP (-30.5 kJ/mol), creatine phosphate (-43 kJ/mol).
Glycolysis Energy Steps
| Step | Compound | Enzyme | ΔG°’ (kJ/mol) | Role |
|---|---|---|---|---|
| 7 | 1,3-BPG → 3-PG | Phosphoglycerate kinase | -18.5 (coupled) | ATP formation |
| 10 | PEP → Pyruvate | Pyruvate kinase | -31.7 | ATP formation |
Common Misconceptions
AMP acts as an energy sensor, not donor, with weak ester bonds. Vitamin K aids gamma-carboxylation but holds no high-energy phosphate. For CSIR NET, focus on ΔG°’ thresholds and structures.
