Question

When ATP is used as the energy currency to make, say, reaction X + Y → Z happen, is what happens on a physical level down at the molecular scale that during the reaction ATP + H2O → ADP + PiΔG˚ = −30.5 kJ/mol (−7.3 kcal/mol) that 30.5 kJ/ mol is conferred by ATP molecules physically bumping around the reactants X and Y, the kinetic energy of the above reaction being what does it?

Answer 1

ATP hydrolysis releases energy not by direct kinetic interactions but by breaking a high-energy phosphate bond, releasing free energy used for cellular work through energy coupling and phosphorylation processes, such as in the sodium-potassium pump.

Step-by-step explanation:

When ATP is used as the energy currency in biochemical reactions such as X + Y → Z, the molecular-scale events involve a process known as hydrolysis. This reaction, ATP + H₂O → ADP + Pi, releases free energy of -30.5 kJ/mol under standard conditions, but this value is nearly doubled inside living cells to -57 kJ/mol.

The free energy released from hydrolyzing ATP does not come from ATP molecules 'bumping around' reactants, but from the energy stored in the high-energy phosphate bond of ATP.

Energy coupling is a crucial concept in cellular metabolism. Cells harness the energy from exergonic reactions (like ATP hydrolysis) to drive endergonic reactions (such as the sodium-potassium pump operation). This is achieved through the transfer of the phosphate group from ATP to another molecule, a process called phosphorylation.

The phosphorylated molecule gains free energy and can then undergo conformational changes to perform work, as seen with the sodium-potassium pump which requires the hydrolysis of ATP for each cycle of ion transport.