![Q.51 The ∆G ́ and K ́eq values of ATP hydrolysis are -32.34 kJ mol-1 and 4.6 x105, respectively. The ∆G ́ and K ́eq values of enzymatic hydrolysis of glucose-6- phosphate to glucose and phosphate are -13.18 kJ mol-1 and 203.8, respectively. The ∆G ́ value of reaction of glucose-6-phosphate formation from glucose and ATP by hexokinase is _______ kJ mol-1 (rounded off to 2 decimal places). [All reactions are carried out at pH 7.0 and 25 °C].](data:image/svg+xml;base64,PHN2ZyB2aWV3Qm94PSIwIDAgMTkyMCAxMDgwIiB3aWR0aD0iMTkyMCIgaGVpZ2h0PSIxMDgwIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciPjwvc3ZnPg==)
Q.51 The ∆G ́ and K ́eq values of ATP hydrolysis are –32.34 kJ mol–1 and 4.6 x105,
respectively. The ∆G ́ and K ́eq values of enzymatic hydrolysis of glucose–6–
phosphate to glucose and phosphate are –13.18 kJ mol–1 and 203.8, respectively. The
∆G ́ value of reaction of glucose–6–phosphate formation from glucose and ATP by
hexokinase is _______ kJ mol–1 (rounded off to 2 decimal places). [All reactions are
carried out at pH 7.0 and 25 °C].
The ΔG° value for the hexokinase reaction (glucose + ATP → glucose-6-phosphate) is -19.16 kJ/mol.
This coupled reaction drives glucose phosphorylation using ATP hydrolysis energy under standard conditions at pH 7.0 and 25°C. The calculation reverses the given glucose-6-phosphate hydrolysis and adds ATP hydrolysis ΔG° values.
Reaction Breakdown
Hexokinase catalyzes: glucose + ATP ⇌ glucose-6-phosphate + ADP.
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ATP hydrolysis: ATP + H₂O → ADP + Pᵢ, ΔG°’ = -32.34 kJ/mol, K’eq = 4.6 × 10⁵
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Glucose-6-phosphate hydrolysis: glucose-6-phosphate + H₂O → glucose + Pᵢ, ΔG°’ = -13.18 kJ/mol, K’eq = 203.8
The net reaction cancels Pᵢ and H₂O: ΔG°’ = ΔG°’_ATP + (-ΔG°’_G6P hydrolysis) = -32.34 + 13.18 = -19.16 kJ/mol.
Verification Methods
K’eq confirms via ΔG°’ = -RT ln K’eq (R = 0.008314 kJ/mol·K, T = 298 K).
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Calculated K_ATP ≈ 4.67 × 10⁵ (matches given) [calculation]
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Calculated K_G6P ≈ 204 (matches given)
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K’eq_hexokinase = K_ATP / K_G6P = 4.6 × 10⁵ / 203.8 ≈ 2257
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ΔG°’_hexokinase = -RT ln(2257) ≈ -19.16 kJ/mol [calculation]
Negative ΔG°’ indicates spontaneity, essential for glycolysis initiation.
Introduction: Mastering ΔG° in Hexokinase Reaction for CSIR NET
In CSIR NET Life Sciences, understanding ΔG glucose-6-phosphate formation hexokinase is crucial for biochemistry and energetics. This first glycolysis step couples endergonic glucose phosphorylation to exergonic ATP hydrolysis, yielding ΔG°’ = -19.16 kJ/mol at pH 7.0, 25°C—making it spontaneous and irreversible in vivo.
Detailed Calculation: Coupled Reactions Explained
Step 1: ATP hydrolysis releases energy: ATP + H₂O → ADP + Pᵢ (ΔG°’ = -32.34 kJ/mol).
Step 2: Reverse G6P hydrolysis (endergonic): glucose + Pᵢ → glucose-6-phosphate (ΔG°’ = +13.18 kJ/mol).
Step 3: Net: glucose + ATP → glucose-6-phosphate + ADP (ΔG°’ = -32.34 + 13.18 = -19.16 kJ/mol).
K’eq verification: K_hexokinase = 4.6 × 10⁵ / 203.8 ≈ 2257 (ΔG°’ matches via -RT ln K). [calculation]
| Reaction | ΔG°’ (kJ/mol) | K’eq | Direction |
|---|---|---|---|
| ATP hydrolysis | -32.34 | 4.6 × 10⁵ | Highly favorable |
| G6P hydrolysis | -13.18 | 203.8 | Favorable |
| Hexokinase (net) | -19.16 | 2257 | Favorable |
Biological Significance in Glycolysis
Hexokinase traps glucose as G6P, committing it to metabolism. Negative ΔG°’ (-19.16 kJ/mol) ensures flux despite cellular [ATP]/[ADP] ratios. Feedback inhibition by G6P regulates.
CSIR NET tip: Always add ΔG°’ values for coupled reactions; reverse endergonic steps.
