Coupled reactions

[shanyk]

Hello,
Are all endothermic reaction take their energy from a coupled exothermic reaction? Is it possible that an endothermic reaction would take it's energy from the physical process of cooloing the environment?
If so- why are there so many coupled reactions in cell biology if it can just take it's energy from the cell environment? (Is it for keeping a constant cell tempreture or is there any chemical reason)?
In other words- when is an endothermic reaction needs to be coupled?
Thank you very much!

[zhermes]

You're exactly right. If you took the energy for an endothermic reaction from the environment---you would change the environment, and therefore not be in equilibrium (or perhaps a better word is homeostasis). Therefore, the only way to get energy effectively is to couple exothermic to endothermic reactions. This can be done in non-classically chemical ways----e.g. using a photon, or mechanical energy, or mass action, etc etc.

[DDTea]

In a biochemical context, it is critical to keep temperature mostly constant. Remember, our bodies operate at 98.6 F and 1 atm pressure: we can't do any brutal chemistry! Also, these are the conditions that enzymes are made to function. With the amount of processes going on in cells, without coupled reactions there would be some serious temperature changes. Enzymes might denature or simply not function properly. That's no way to maintain an organism.