I was wondering what exactly a coupled reaction is and why cells
couple them. I read the wikipedia article as well as several
others, such as life.illinois.edu but I still don't get it.
Could someone explain it to me? It's pretty simple. A reaction
occurs that releases energy (like ATP losing a phosphate to
become ADP + Pi). If this is uncoupled, the energy will merely
turn into heat. If it is coupled, then it can be used to fuel
some other process. For instance, if you couple the ATP -> ADP
reaction to a certain protein, the energy can be used to modify
the shape of that protein. A coupled biochemical reaction is one
where the free energy of a thermodynamically favourable reaction
(such as the hydrolysis of ATP) is used to 'drive' a
thermodynamically unfavourable one, by coupling or
'mechanistically joining' the two reactions. To put it another
way, two (or more) reactions may be combined by an enzyme (for
example) such that a spontaneous reaction may be made 'drive' an
unspontaneous one. Such reactions may