Question

Which statement explaining the importance of electrostatic repulsion for the phosphoryl-transfer potential of ATP is TRUE?

1. Juxtaposition of negative charges of β and γ phosphoryl groups gives a lower free energy than that for free orthophosphate.

2. Water more readily stabilizes negative charges of products of ATP hydrolysis than of ATP itself.

3. At a physiological pH, hydrolysis of ATP decreases the number of negative charges.

4. Juxtaposition of negative charges of α and β phosphoryl groups gives a lower free energy than that for free orthophosphate.

5. A close proximity between phosphoryl groups of ATP gives a higher energy than does free orthophosphate in a solution.

Answer 1

3) The hydrolytic cleavage of the terminal phosphoric acid anhydride (phosphoanhydride) bond in ATP separates one of the three negatively charged phosphates and thus relieves some of the electrostatic repulsion in ATP; the hydrolysis-released Pi (HPO42-) is stabilized by the formation of several forms of resonance which are not possible in ATP; and the other direct hydrolysis product, ADP2- The small concentration of the target components supports the hydrolysis reaction, by mass motion.

While its hydrolysis is strongly exergonic (i.e. ATP = -30.5 kJ / mol), ATP is kinetically stable to non-enzymatic breakdown at pH 7 due to reasonably strong activation energy for ATP hydrolysis. Rapid cleavage of the anhydride bonds with phosphoric acid happens only after an enzyme catalyzes.