Q.36 Which one of the following molecules does NOT contain phosphoanhydride
bond(s)?
(A) Adenosine diphosphate
(B) Adenosine triphosphate
(C) Fructose–1,6–bisphosphate
(D) Pyrophosphate
Fructose-1,6-bisphosphate does not contain phosphoanhydride bonds. This molecule from glycolysis features phosphoester linkages instead, unlike the other options which have high-energy phosphoanhydride bonds between phosphate groups.
Phosphoanhydride Bond Basics
Phosphoanhydride bonds link two phosphate groups directly via an oxygen bridge (P-O-P), forming high-energy acid anhydride structures. These bonds release substantial energy upon hydrolysis (ΔG ≈ -30.5 kJ/mol), powering cellular processes like ATP utilization. In contrast, phosphoester bonds connect phosphate to an alcohol group on sugars (P-O-C), storing far less energy.
Option Analysis
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(A) Adenosine diphosphate (ADP): Contains one phosphoanhydride bond between the β and α phosphate groups, enabling energy transfer similar to ATP but with lower capacity.
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(B) Adenosine triphosphate (ATP): Features two phosphoanhydride bonds (α-β and β-γ), the primary energy currency in cells via hydrolysis to ADP or AMP.
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(C) Fructose-1,6-bisphosphate: Lacks phosphoanhydride bonds; its phosphates at C1 and C6 form phosphoester bonds with the fructose hydroxyl groups, as confirmed by its glycolytic structure.
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(D) Pyrophosphate (PPi): Consists entirely of a single phosphoanhydride bond (H4P2O7), a byproduct of biosynthetic reactions hydrolyzed by pyrophosphatases.
Introduction to Phosphoanhydride Bonds in Biochemistry
Phosphoanhydride bonds power cellular metabolism as high-energy linkages in molecules like ATP and ADP. Critical for CSIR NET Life Sciences, understanding phosphoanhydride bonds distinguishes them from phosphoester bonds in sugars like Fructose-1,6-bisphosphate. This guide analyzes Q.36 options for exam success.
What Are Phosphoanhydride Bonds?
These P-O-P bonds form via dehydration of phosphoric acid derivatives, yielding exergonic hydrolysis for energy transfer. Found in ATP (two bonds), ADP (one), and pyrophosphate, they drive glycolysis, biosynthesis, and active transport. Unlike stable phosphoester bonds (P-O-C), phosphoanhydride bonds store ~7-30 kJ/mol more free energy.
Detailed Breakdown of Each Molecule
| Molecule | Bond Type | Contains Phosphoanhydride? | Role in Metabolism |
|---|---|---|---|
| ADP | One P-O-P (β-α) | Yes | ATP hydrolysis product; energy intermediate |
| ATP | Two P-O-P (α-β, β-γ) | Yes | Universal energy currency |
| Fructose-1,6-bisphosphate | Two P-O-C esters | No | Glycolysis intermediate (PFK-1 product) |
| Pyrophosphate | One P-O-P | Yes | Biosynthetic byproduct; hydrolyzed for irreversibility |
Fructose-1,6-bisphosphate uses ATP’s phosphoanhydride bond hydrolysis to form its phosphoester bonds, confirming it lacks them.
Why Fructose-1,6-Bisphosphate Lacks Them
In glycolysis, phosphofructokinase-1 transfers phosphate from ATP to fructose-6-phosphate, creating ester linkages at C1/C6—no anhydride formed. This commits glucose to breakdown without high-energy storage like in nucleotides.
Exam Tips for CSIR NET
Differentiate: Nucleotide polyphosphates (ADP/ATP/PPi) have phosphoanhydride bonds; sugar bisphosphates like F-1,6-BP have esters. Recall: Hydrolysis energy drops ester << anhydride. Practice with glycolysis pathways for related questions.
