Key features of oxidative phosphorylation Which statement describes something that is <em>not</em> a feature of oxidative phosphorylation in mitochondria?

Introduction / Context:
There are two fundamental modes of ATP formation: substrate-level phosphorylation and oxidative phosphorylation. Distinguishing these mechanisms is essential for mapping where ATP arises in metabolism.

Given Data / Assumptions:

• Oxidative phosphorylation occurs in mitochondria using electron transport to build PMF.
• ATP synthase (Complex V) uses PMF to synthesize ATP.
• Substrate-level phosphorylation transfers phosphate directly from an intermediate to ADP (e.g., in glycolysis and TCA at succinyl-CoA synthetase).

Concept / Approach:
Oxidative phosphorylation relies on proton pumping by respiratory complexes I, III, and IV, generating ΔΨ and ΔpH. ATP synthase then catalyzes ADP + Pi → ATP using this PMF. No direct high-energy phosphate transfer from a metabolic intermediate to ADP occurs in this process.

Step-by-Step Solution:
Identify the defining feature: chemiosmotic coupling to ATP synthase.Note that substrate-level ATP formation is separate and occurs in cytosol/mitochondrial matrix at specific enzymes.Conclude that direct phosphate transfer is not a feature of oxidative phosphorylation.

Verification / Alternative check:
Inhibitors/uncouplers (oligomycin, FCCP) that affect PMF or ATP synthase specifically reduce oxidative phosphorylation but not substrate-level phosphorylation steps, underscoring their mechanistic differences.

Why Other Options Are Wrong:
Electrochemical gradient, ATP synthase, protonmotive force, and coupling to electron transport are all core features of oxidative phosphorylation.

Common Pitfalls:
Confusing succinyl-CoA synthetase (substrate-level phosphorylation) with ATP synthase; assuming all mitochondrial ATP arises from the same mechanism.

Final Answer:
Direct transfer of phosphate from a substrate molecule to ADP.