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Biochemistry Questions

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ATP-4(aq) + H2O(l) ↔ ADP-3(aq) + H3O+(l) + HPO-24

Calculate the fraction of adenosine that exists in each form (ATP & ADP) at pH = 7 at 298 K and 310 K. Assume the buffer keeps the pH @ 7 no matter how much ATP is hydrolyzed. HPO4 concentration is at 0.006 M.

Solution: pH = 7

At 298 K, ΔGorxn = -RTlnKeq = -30.5 x 103 J/mol (standard value for ATP hydrolysis)

Hence -8.314 J/mol K x 298K x ln[ADP][HPO42-]/[ATP] = -30.5 x 103 J/mol (I've ignored H+ as you have indicated it as being a pure liquid and not aqueous)

[ADP]/[ATP] = 36.6 x 106 (Let me know if you need the ratio when H+ is aqueous)

Now, ΔHorxn = -20 x 103 J/mol (standard value for ATP hydrolysis)

ln K310 = lnK298 - (ΔHorxn / R)(1/ 310 - 1/298)

K310 = 15.9 x 104