A revolving door through which energy passes during transfer from catabolic to anabolic pathways?

• A. ATP cycle
• B. Metabolic gateway
• C. Energy shuttle
• D. Phosphorylation cycle

Answer: (A)

The energy currency of the cell serves as the revolving door between energy-releasing and energy-using steps. In catabolic processes, energy is captured to form ATP from ADP and inorganic phosphate. That ATP then travels to anabolic processes, where its high-energy phosphate bonds are broken to fuel biosynthetic reactions. This ongoing cycle of making and using ATP links the breakdown of nutrients to the synthesis of biomolecules, so the term that best captures this continuous transfer is the ATP cycle. Other terms aren’t standard descriptions of this overarching flow—phosphorylation is a part of the process, but it doesn’t name the whole cycle; while “energy shuttle” or “metabolic gateway” aren’t established labels for this mechanism.