Enzyme Lab - Introduction.



Enzymes are large molecules, almost always proteins, that act in living systems as catalysts:  they help speed up particular chemical reactions by lowering the activation energy, the energy needed to start and sustain the reactions.  These molecules have “dents” – active sites - on their surfaces into which the reacting chemicals, called substrates, fit.  Once the active site has a substrate in it, the enzyme molecule changes in a way that helps the substrate react.   If this was just a simple chemical reaction, then it would speed up with increased temperature, but with enzymes involved, there are more considerations.


Enzymes, like most large biological molecules, are held in their working shape by a lot of internal hydrogen bonds.  When their shapes change, enzymes will work poorly or not at all.  Hydrogen bonds, loose attractions between partially changed areas, can be broken by vibrating the molecule with heat – too much heat may permanently unwind the molecule, denaturing it.  Ions that can float into the molecules affect hydrogen bonds as well, so that a change in pH, changing the “normal” complement of H+ or OH-, can change the shape of the molecules as well.   Because of these effects, enzymes have particular temperatures and pH levels at which they work their best, the optimums.


Enzyme molecules, like workers in a manufacturing plant, produce changes in objects but don’t change themselves.  Like a roomful of workers, if you give them more to do, they can be more productive, up to the point every worker is working constantly – adding to the workload at that point won’t change the production rate.  This process – add substrate and the reaction rate goes up, but keep adding substrate and the rise in rate will slow and then flatten out – is called Michaelis-Menten kinetics.







General Biology 2 - Molecules and Cells

Lab Exercise Index

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