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The complete breakdown of one glucose molecule results in the formation of 12 molecules of NADPH2 via the HMP pathway. Which of the following statements correctly describes substrate-level phosphorylation?

1. One example of substrate-level phosphorylation in the citric acid cycle involves the following reaction: CH2-COO GDP + Pi → GTP + CoA-SH | | | | Succinate-CoA.
2. Other instances of substrate-level phosphorylation include these reactions: 1,3-bisphosphoglycerate + ADP → 3-phosphoglycerate + ATP, Phosphoenolpyruvate + ADP → pyruvate + ATP, and Acetyl phosphate + ADP → acetate + ATP (similar reactions occur for other alkanoic acids).
3. Substrate-level phosphorylation refers to the synthesis of ATP from ADP through the direct transfer of a high-energy phosphate group from a phosphorylated intermediate during an exergonic catabolic reaction.
4. Oxidative phosphorylation is the mechanism by which ATP is generated as electrons are transferred from NADH or FADH2 to oxygen via a chain of electron carriers. This process occurs in mitochondria and is the primary ATP source in aerobic organisms.

Correct answer: Substrate-level phosphorylation refers to the synthesis of ATP from ADP through the direct transfer of a high-energy phosphate group from a phosphorylated intermediate during an exergonic catabolic reaction.

Solution

The correct statement is the definition of substrate-level phosphorylation: ATP is made directly from ADP by transferring a phosphate from a high-energy intermediate. This is different from oxidative phosphorylation, which depends on the electron transport chain.

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