Laws of Thermodynamics

The catabolic reactions release energy that anabolic reactions use to make something (like polypeptide chains from amino acids), so, they increase the entropy of the surroundings by releasing heat. The anabolic pathways, on the other hand, are non spontaneous because they need an input of energy to happen. Do they also release some of the heat since it is and energy transformation according to the 2nd law of thermodynamics? So, when the molecules order themselves they still release some heat and raise the entropy of the universe?

Hey Sofia! You are correct. Both catabolic and anabolic reactions are subject to the 2nd law of thermodynamics, which states that in any energy transformation, some energy is always lost as heat, leading to an increase in the overall entropy of the universe.

Catabolic reactions break down complex molecules into simpler ones and release energy in the process. This energy is often in the form of ATP, which can be used to drive anabolic reactions. In this process, some of the energy is inevitably lost as heat, contributing to an increase in the entropy of the surroundings.

Anabolic reactions, on the other hand, require energy input to synthesize complex molecules from simpler ones. While they decrease the entropy locally by creating more ordered structures (e.g., synthesizing polypeptide chains from amino acids), they also release heat as energy is transferred during the reaction. This release of heat contributes to an overall increase in the entropy of the universe.

In summary, although anabolic pathways create order within molecules, the energy transformations involved still result in the release of heat and a net increase in the entropy of the universe, in accordance with the 2nd law of thermodynamics.


Hi, Ari! Thank you fro your reply. Although, will the anabolic reactions still be considered non spantaneous?

Yes, for the level of the IMAT exam we only refer to the specific reaction itself, usually isolated, so energy must be invested from somewhere in order to drive anabolic reactions, for the IMAT it is most of the times in the form of ATP.

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