What is the difference between competitive and non-competitive inhibition?

Competitive inhibition means the inhibitor molecule is a similar shape to the normal substrate molecule. Because of this similar shape, the inhibitor molecule is also able to bind to the active site of the enzyme. This makes sense as if two molecules have a similar shape, the enzyme is unable to discriminate between them and therefore both molecules are able to bind (and form temporary bonds) with the active site. As both molecules are competing for the same active site, increasing the concentration of the inhibitor will decrease the probability of the substrate forming an enzyme-substrate complex, and therefore rate of reaction will slow. However, the reverse is also true, meaning inhibition can be overcome by adding more substrate as this decreases the chance of the inhibitor binding to the active site.In comparison, non-competitive inhibition means the inhibitor binds to a site on the enzyme which is not the active site. This changes the shape of the active site (making it harder for the substrate molecules to bind to it and thus, slowing the rate of reaction). This slower rate of reaction cannot be overcome by adding more substrate as the substrate and inhibitor are competing for different sites on the enzyme.