What does heat do to an enzyme and why can enzymes not be 'killed'?

Enzymes are proteins that are polymers made up of amino acid building blocks. When enzymes are made by cells, they are made as a long chain of amino acids that after some time, can fold up to form a specific, three-dimensional (3D) shape. This 3D shape is held together by a series of chemical bonds, such as hydrogen bonding, and it is this specific shape that determines what reaction an enzyme catalyses.When enzymes are heated up, they become denatured. This means that the protein no longer works as an enzyme (to catalyse reactions) as the energy provided by the heat is enough to break the chemical bonds that hold it in a specific 3D shape. This unravels the amino acid chain and there is no enzyme activity any more. Enzymes cannot be 'killed' as they were never alive in the first place - they are simply a polymer of amino acids and are a part of living organisms.