Standard Enzyme Reaction
Imagine that an enzyme and a substrate are a man and a woman. The substrate binds to the enzyme’s complementary ‘active site’ and a chemical reaction ensues (sex). As a result of this, a product is formed (a child). The enzyme is not consumed in the reaction and can catalyse further chemical reactions (what a player!).
A competitive inhibitor is another woman (home wrecker!). She is competing with the substrate for the enzyme’s ‘active site’. If the competitive inhibitor binds to the enzyme, she will block the active site and prevent a chemical reaction from occurring with the substrate. Hence no product will be formed.
A non-competitive inhibitor is another man. He is not competing with the substrate for the active site. Instead, he will bind to an alternate allosteric site (i.e. the rear end). If the non-competitive inhibitor binds to the enzyme, it causes a ‘conformational change’ in the shape of the active site, such that the active site loses its affinity for the substrate (i.e. the 'active site' becomes flaccid around the substrate). Hence no product will be formed.
End-product inhibition is a form of negative feedback whereby the product inhibits its own further production. The more product created by the enzyme (i.e. the more offspring he has), the less time he will have available for further chemical reactions. When the product level drops (the children grow up and leave home), the enzyme becomes free to undertake more chemical reactions. End-product inhibition ensures product levels remain tightly regulated (prevents too many kids!).