Biological systems

[Kate Zeile 2D]

The textbook states that a reaction that produces a lot of entropy can drive a non spontaneous reaction forward, and that this is used extensively in biological systems. Can someone please explain to me how this coupling works? I do not understand how a reaction with excess entropy can make another reaction proceed in the forward direction. Does it act as a kind of catalyst?

[Chris Lamb 1G]

One reaction releases energy (like breaking ATP). This energy can be used to drive a reaction that is not favorable (like pumping ions across a barrier).

[David Zhou 1L]

Many of the reaction pathways that are taught in biology are long chains of these connected reactions, like in glycolysis, the Krebs/Citric acid cycle, and the Calvin cycle. These metabolic pathways are crucial to the survival of an enormous number of organisms, and are happening all the time.

[Thomas Gimeno]

This is used all the time because its an effective way of getting unfavorable reactions to occur. You used the energy produced by one reaction to make another reaction go. For example, this is how all of the electron transport chain works. An electron is given to a molecule which is favorable, and this allows a hydrogen to be pumped which is unfavorable. The electron then gets taken and given to more molecules which is all favorable and that gives the energy to pump another hydrogen ion which again, is unfavorable. This is one of the most important functions of life and it relies on that process.

[Gicelle Rubin 1E]

Thanks for asking this question. I was also confused but I'm glad there are responses! :)

[305561744]

Biological energy coupling occurs when an exergonic (like exothermic, heat releasing) drives an endergonic (endothermic, heat absorbing) process. Excess energy is used rather than wasted.

[Narin Maisha 2H]

Since one reaction would release energy, another reaction could take in that energy to be able to help and put an unfavorable reaction into action.

[805754009]

To my understanding, when a reaction occurs that produces excess entropy, there is a higher level of disorder in the resulting products, resulting in increased collisions, pushing the subsequent reaction forward. This can help a reaction that would normally not proceed spontaneously occur, without artificially having to add energy.