A biochemist needs to drive the phosphorylation of glucose to glucose-6-phosphate…

CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

A biochemist needs to drive the phosphorylation of glucose to glucose-6-phosphate under physiological conditions. The direct phosphorylation reaction has a standard Gibbs free-energy change of

\Delta G^{\circ}=+13\,\text{kJ mol}^{-1}

. To power this step, the biochemist can choose one of the three reactions in Table 1. Table 1 Candidate Driving Reactions (all values at

298\,\text{K}

pH\,=7.0

)

Reaction (all aqueous)	$\Delta G^{\circ}\,(\text{kJ mol}^{-1})$
(I) ATP $^{4-}$ → ADP $^{3-}$ + P $_\text{i}^{2-}$	−30
(II) PEP → pyruvate $^{-}$ + P $_\text{i}^{2-}$	−62
(III) phosphocreatine $^{2-}$ → creatine + P $_\text{i}^{2-}$	−43

Because the laboratory protocol prohibits direct phosphate transfer between the driving reaction and the glucose substrate, an enzyme must split the driving reaction into two half-reactions that share a phosphorylated intermediate. Only candidate reactions whose mechanism allows formation of such an intermediate are acceptable. (a) Identification and mechanistic explanation (b) Construction of overall reaction and calculation of

\Delta G^{\circ}_{\text{overall}}

Related theory

Browse the problem library