NANP Board Practice Exam

What accelerates the Krebs Cycle?

1. Conversion of ADP to ATP

2. Decrease in oxygen levels

3. Increase in ADP:ATP ratio

4. Reduction of NAD+

The correct answer is: Increase in ADP:ATP ratio

The Krebs Cycle is a series of chemical reactions that take place in the mitochondria of cells and are responsible for converting nutrients into energy. The Krebs Cycle is only able to occur when there is a sufficient supply of ATP, the cell's primary energy source. This is where the increase in ADPATP ratio becomes significant. An increase in the ADP:ATP ratio triggers the Krebs Cycle to accelerate in order to produce more ATP. This process is also known as negative feedback, where a decrease in one component (ATP) causes an increase in another (ADP) in order to maintain balance in the cell. The other options are incorrect because they are either not related to the Krebs Cycle or have the opposite effect of what is needed for the cycle to accelerate. Conversion of ADP to ATP, option A, is a result of the Krebs Cycle and not what triggers its acceleration. Decrease in oxygen levels, option B, would actually slow down the Krebs Cycle as oxygen is needed as the final electron acceptor in the electron transport chain, a part of the Krebs Cycle. Reduction of NAD+, option D, is also incorrect as NAD+ is needed in its oxidized form