Inhibitors are molecules that bind to enzymes to reduce their activity.

Reversible inhibitors are those that form weak bonds with the enzyme.

They temporarily prevent that enzyme from catalysing another enzyme-controlled reaction.

Irreversible inhibitors are those that that form strong bonds with the enzyme.

They permanently prevent that enzyme from catalysing another enzyme-controlled reaction.

Competitive inhibitors are molecules that bind to the active site of the enzyme.

Non-competitive inhibitors are molecules that bind to enzymes away from the active site. 

They bind to another site called the allosteric site.

Competitive inhibitors decrease the rate of reaction by preventing the formation of enzyme-substrate complexes. 

Competitive inhibitors have a similar shape to a substrate and bind to the active site of the enzyme.

This prevents the substrate(s) from binding to form enzyme-substrate complexes. 

The effect of competitive inhibitors can be reduced by by increasing the substrate concentration.  This means there will be more substrate molecules, making substrates more likely to bind to active sites than inhibitor molecules. 

Non-competitive inhibitors decrease the rate of reaction by preventing enzyme-substrate complexes from forming. 

Non-competitive inhibitors bind to enzymes away from the active site which changes the tertiary structure of the enzyme, causing the active site to change shape.

This means the active site is no longer complementary to the substrate(s), so the substrate(s) cannot bind to form an enzyme-substrate complex. 

Increasing substrate concentration has no effect on the rate of reaction because non-competitive inhibitors do not compete with the substrate to bind to the active site.