Why is the tertiary structure of an enzyme essential to its function?

Firstly, explain what tertiary structure means - the overall 3D structure of a polypeptide chain
This 3D shape is essential to enzyme function (aka catalysing biological reactions), as this shape will determine the shape of the enzyme's active site. The shape of the active site is complementary to the substrates the enzyme is catalysed - the 'lock and key' model. Therefore, if the structure were to change and alter the shape of the active site, it would no longer be complementary to the shape of the substrate, and it could not catalyse the reaction. could include a diagram explaining the lock and key model if necessary