Bioenergetics of glucose oxidation: The released energy from catabolizing glucose is primarily captured and stored in which immediate cellular energy currency?

Introduction / Context: Cells extract energy from glucose through glycolysis, the citric acid cycle, and oxidative phosphorylation. The question asks which molecule directly stores this energy in a readily usable form for cellular work.

Given Data / Assumptions:

• Glucose oxidation proceeds stepwise with coupling to energy carriers.
• Cells require an immediately usable chemical energy form for biosynthesis, transport, and mechanical work.
• Multiple intermediates exist (NADH, proton motive force), but not all are the final currency for most work.

Concept / Approach: Adenosine triphosphate (ATP) is the universal energy currency. Its high-energy phosphoanhydride bonds can be hydrolyzed to drive endergonic reactions via coupling, phosphorylating intermediates or enzymes to change reaction energetics.

Step-by-Step Solution: Glycolysis yields ATP directly by substrate-level phosphorylation and NADH for later ATP formation. Mitochondrial oxidative phosphorylation converts the energy of NADH/FADH2 into a proton gradient and then to ATP via ATP synthase. Among options, ATP is the molecule cells use directly for work. Therefore, select ATP as the stored, spendable energy unit.

Verification / Alternative check: ATP hydrolysis (ATP → ADP + Pi) releases about 7.3 kcal/mol under standard conditions and more in vivo, powering transporters, kinases, and motor proteins.

Why Other Options Are Wrong: Proton gradients are intermediates used to synthesize ATP; ADP is the lower-energy form; NAD+ is an oxidized carrier, not the store; coenzyme Q is part of electron transport, not the universal energy currency.

Common Pitfalls: Equating proton motive force with the final currency; confusing carriers (NADH/FADH2) with ATP.

Final Answer: ATP.