A. How does the generation of ATP by oxidative phosphorylation differ from ATP generation by substrate-level phosphorylation?

Question

B. What catabolic process uses substrate-level phosphorylation, and how many ATP molecules are generated in this way in the reaction pathway?
C. Where does oxidative phosphorylation take place, and what other processes are required for this to occur?

Answer 1

A. In oxidative phosphorylation, molecular oxygen is required to produce ATP, by means of a multistage, chemiosmotic process (see Chapter 14), while in substrate-level phosphorylation, the energy released by the enzyme-catalyzed oxidation of a substrate generates ATP directly.
B. Glycolysis uses substrate-level phosphorylation and generates two ATP molecules for each glucose molecule oxidized to pyruvate molecules (four total ATPs, but two of these are hydrolyzed in the first few steps of the pathway).
C. Oxidative phosphorylation takes place in mitochondria as part of a multistage oxidation process. First, the citric acid cycle generates NADH and FADH2, which donate their high-energy electrons to the electron-transport chain. These electrons ultimately reduce molecular oxygen to water, and the energy of their oxidation is used to pump protons across a membrane. The proton gradient thereby produced is in turn harnessed by the enzyme ATP synthase to drive the production of ATP from ADP and inorganic phosphate.