How do we differenciate between catabolic and anabolic reactions?

According to my researches;

Catabolic Reactions

Catabolic reactions (also called “catabolism”) break down larger, more complex molecules into smaller molecules and release energy in the process. The smaller end products of a catabolic reaction may be released as waste or they may be fed into other reactions. The energy that is released by catabolic reactions can be captured and used in many ways. Some of the energy is released as heat and increases the temperature of the cell. Sometimes the energy is stored in the chemical bonds of another molecule. And sometimes it can be used to do work, such as movement of cellular machinery to power the active transport of materials across cell membranes. Catabolic reactions are central to biological processes such as cellular respiration and the digestion of food molecules.

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Anabolic Reactions

Anabolic reactions (also referred to as "anabolism") use energy to build more complex molecules from relatively simple raw materials. “Anabolic” and “catabolic” sound similar but are opposites. To remember the difference, it may help to think about how “anabolic steroids” promote the buildup of muscle mass. All of the complex molecules of life — carbohydrates, lipids, proteins, nucleic acids — are generated by anabolic reactions. Anabolic reactions are central to processes like photosynthesis, protein synthesis, and DNA replication.

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Here are my questions

  • Is there water in every chemical reaction?

  • Do i just need to look at water ($H_{2}O$)?



1 Answer 1


Starting of with the basics, reactions are the breaking of bonds in the reactants and the forming of bonds in the products.

To answer your questions about water, there is not always H2O present, although most of the times there is water. You are referring to the hydrolysis and dehydration synthesis reactions, in which water is added or removed, to break down and combine molecules, respectively.

Catabolic reactions are more defined as the net release of energy in the reaction. They break down bigger molecules to smaller molecules. There is a need for energy input to begin the reaction and break the bonds of the reactants, however, the release of energy when the bonds of the products form are far greater, resulting in a net release of energy.

Anabolic reactions are essentially the opposite, where smaller molecules are combined and built up to larger macromolecules, many times with the removal of H2O. This results in a net decrease in free energy, as energy is absorbed/stored in the larger molecule. Energy inputted to break bonds of the reactants are far greater than the small energy released as bonds form.

As you will learn soon, these reactions can be characterized by exergonic/exothermic, and endergonic/endothermic reactions. They can be considered synonymous in many cases.


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