Explain how a mutation in DNA could cause a non functioning enzyme to be formed

A mutation could change the order of DNA bases which would alter the type of amino acid produced from a DNA triplet. Therefore, the enzyme, which is a protein, formed from these amino acids would be different. This may change the shape of the enzyme’s active site so it would no longer be a complementary shape to the substrate. As part of the lock and key theory, enzymes and substrates need to have complementary shapes to complete their reaction so if the active site shape is changed, the reaction cannot take place and the enzyme would not be able to function as it would have done with the normal DNA base sequence.