AFAA Personal Trainer Certification Practice Exam

In which cycle does acetyl CoA enter for further energy extraction?

1. Calvin cycle

2. Krebs cycle

3. Glycolysis

4. Beta oxidation

The correct answer is: Krebs cycle

Acetyl CoA enters the Krebs cycle, also known as the citric acid cycle, for further energy extraction from carbohydrates, fats, and proteins. After the breakdown of glucose through glycolysis or the breakdown of fatty acids through beta-oxidation, acetyl CoA is produced and enters the Krebs cycle. Within the Krebs cycle, acetyl CoA combines with oxaloacetate to form citrate, and through a series of chemical reactions, it is oxidized to release high-energy electrons carried by NADH and FADH2. These high-energy electrons are then used in the electron transport chain to generate ATP, the primary energy currency of the cell. This cycle is fundamental for cellular respiration, allowing the body to extract maximal energy from the nutrients consumed. The other cycles mentioned do not involve acetyl CoA directly. The Calvin cycle is associated with photosynthesis, glycolysis is the pathway that precedes the production of acetyl CoA from glucose, and beta oxidation pertains to the breakdown of fatty acids into acetyl CoA. Therefore, the Krebs cycle is the correct pathway for acetyl CoA to enter for energy extraction.