Effect of substrate concentration.
Can be reduced by increasing substrate concentration.
Increasing substrate concentration does not reduce effect of inhibition.
Competitive Inhibition.
The structure of inhibition molecule is similar to that of the substrate. The inhibitors get attached to the active site of the enzyme. It competes with the substrate molecule or for the enzyme. It does not alter the structure of the enzyme. The reaction can be reversed by increasing the substrate concentration. .
Non-Competitive Inhibition.
The structure of the inhibitor molecule is entirely different. The inhibitor forms complex at a point other than the active site. It does not complete with the substrate. It alters the structure of the enzyme in such a way that the substrate may get attached to the active site but products are not formed. The reaction goes on decreasing as more and more inhibitors contact the enzyme till saturation is reached.
b) Why does adding substrate overcome competitive but not noncompetitive inhibition?.
A competitive inhibitor competes for the enzyme's attention and a noncompetitive inhibitor stops the enzyme from working. A competitive inhibitor competes with the substrate to bind to the active site while a noncompetitive inhibitor binds to an allosteric site of the enzyme (one other than the active site). Thus no amount of substrate can overcome or in a sense interfere with the inhibitors binding to an allosteric site.
We can conclude that a competitive inhibitors bind to the active site and prevent substrate from binding, the more substrates that are added the more of a chance the enzyme has of binding to the substrate - overcoming the inhibition. On the other hand, noncompetitive inhibitors bind to an allosteric site and change the shape of the enzyme, so no matter how much substrate is added the enzyme can't work any faster unless the allosteric inhibitor is removed.
Applying Your Knowledge.