Enzymes are very efficient and specific catalyst proteins which react with 1 or few types of substrates in biochemical reactions and are responsible for bringing about almost all of the chemical reactions in living organisms. Enzymes speed up reactions by providing an alternative reaction pathway of lower activation energy. Without enzymes, reactions take place at a rate far too slow for the pace of metabolism which means that they speed up the chemical reactions in living things. Without enzymes, our guts would take weeks to digest our food, our muscles, nerves and bones would not work properly and so on.