Answer: Enzyme has an active site in a particular unique shape which a substrate recognises and bind to.
Explanation: For a reaction to occur, all enzymes have an active site that a specific substrate will bind to forming an enzyme-substrate complex, then a required product is created. Due to this, sometimes a reaction may not occur because of inhibition. Enzyme inhibition is caused by having a molecule with a conformation that resembles a subtrate, the molecule or substance will compete with the substrate for the enzyme active site preventing a reaction to take place. Inhibition may either be competitive as described above or non-competitive where a substance will not directly bind to the active site but will change the conformation of the enzyme in a way that a subtrate will not be able to bind.