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Enzyme dependent to temperature - (Oct/24/2012 )

I was wondering if an enzyme catalysed reaction was less dependant to temperature changes than a spontaneous reaction

I was thinking because the activation energy is lower for the enzyme one that it was less dependant to temperature changes?


is the rate of an enzyme catalysed reaction less dependant to temperature changes than a non spontaneous reaction?

i was thinking it was less dependant because it needs less activation energy, but i have the feeling i'm missing something.



Both depend on temperature, and I'd say it's difficult to say which is less or more dependent on temperature.
In an enzyme catalysed reaction, the reaction can start without having reached the activation energy (because the enzyme catalyses), but the speed of the reaction depends on temperature (a dependence). And the enzyme itself also depends on temperature, as it has an optimum, where it works fastest (too high nothing works anymore when the protein is denatured, too low the speed is lowered to almost zero depending on enzyme; also a kind of dependence).
A spontaneous reaction depends on temperature first by activation energy that has to be high enough and also the reaction speed depends on temp.
So you have different types of dependence on temperature...


In PCR we use Taq polymerase which has temperature optimum of approx. 72o C ( Enzyme Dependent Reaction).
Taq Polymerase is isolated from T.aquaticus whose usual habitat is in hot springs and hydrothermal vent ( Taq poly. working for bacterial metabolism- oh, stil Enzyme and temperature dependent dependent)

MIx all PCR reagent don't add Taq polymerase - try putting at different temperature ( Spontaneous Reaction check)- Note whether you get amplification.

All PCR reagent + Taq pol - try amplifying at different temperature- Perhaps at 60 o C and 90 oC you may not get amplification - More dependence on temperature

In theory even if you don't add enzymes reaction should proceed but when you compare it with enzyme dependent reaction - you have to wait for a long time.
Your experiment face time constraints in this study.

you can study it provided that spontaneous reaction has feasible speed even in absence of enzyme.


You are right, what you are describing is seen using Arrhenius plots.
However, finding systems where you can directly compare enzyme vs non-enzymatic reactions directly is not always straight forward. The Arrhenius plots for enzymes are notoriously non-linear, as Hobgoblin was alluding to; the stability thermodynamics complicates the pure catalytic thermodynamics such that from a practical perspective the rate of an enzymatic reaction is more temperature dependent.