Suzanne O. answered • 10/12/19
International Experience and Multiple State Certifications
The question: As you go above and below the optimum pH and temperature the enzyme activity drops off. Discuss.
I know this is a Biology question, but you have to look at the bigger picture and consider the Chemistry and Physics of the situation.
You did not specify what metabolic process you were looking at, but we know that enzymes either break (catabolic) or build (anabolic) things. Enzymes are complex molecules, they work because their physical and chemical aspects "fit" the physical and chemical aspects of their substrate. We can use the lock and key model to visualize things.
When you change the pH, it goes either more acidic or more basic. From Chemistry, we know that this will change what dissolves and what precipitates, and may break certain kinds of molecules down that we need to be whole or build new ones that we don't want or need. The physical aspects may have been changed, and that would help explain the reduced enzyme activity. Either the substrate is "broken" and no longer fits the enzyme, the enzyme is "broken" and no longer fits the substrate, or there is some other molecule that is causing interference (loose ions bouncing around, bonding where they are not welcome). So there would be something jamming the lock so the key no longer fits.
As for temperature changes, the same sort of thing happens. If you cook, you know that not enough heat means things stay raw. Too much heat and you will burn things. Heat can cause a molecule to change its shape; that little bit of extra energy can cause a protein to uncoil or move an ion from one base carbon to another. Again, the lock and key no longer fit together.
Back to Chemistry. All reactions require a certain amount of energy to get started, cold will potentially slow or stop the reaction. If a reaction is meant to release energy and there is already too much (in the form of heat) around, then feedback mechanisms could stop the reaction as well.
In a nutshell, changing pH and/or temperature away from optimum will slow or halt enzyme activity because either the chemistry is now wrong, the physical aspects have changed or the controlling mechanisms are activated at the wrong moment.
Biology is the one science that has to consider other sciences in its explanations.
