Metabolism, Catabolism, Anabolism, and ATP

Sort reactions by what happens to molecules

Catabolism breaks larger molecules into smaller products. Anabolism builds larger molecules from smaller building blocks. Breaking stored glycogen into smaller units and assembling amino acids into a protein belong on different sides of this comparison.

These processes occur at the same time in different pathways. A cell can break down fuel to help supply the energy needed to build replacement proteins. Eating a meal does not switch catabolism off, and time between meals does not stop all synthesis.

Treat ATP as a transfer step

Energy released by nutrient-processing pathways can help regenerate ATP from ADP and phosphate. ATP hydrolysis can then be coupled to processes such as membrane pumping, molecular movement, or biosynthesis. Cells continually regenerate ATP rather than keeping it as their main long-term energy store.

The useful energy change belongs to the overall reaction and its coupling to cellular work. Simply breaking a chemical bond requires energy; it is misleading to say that bond-breaking alone creates energy. Food, stored fuels, ATP, and heat are different parts of an energy-transfer account.

Follow material as well as energy

On paper, draw two tracks: where building blocks go and how energy is transferred. Use protein construction as your example. Place amino acids on the material track and ATP use on the energy track. This separates the ingredients of a new molecule from the energy required to assemble it.