An enzyme is a protein that speeds up the rate of a reaction in a biological process. For example, enzymes help break down large molecules to release energy during cellular respiration. Which explains how enzymes are involved in energy conversions? 9CEnzymes add the pressure needed for a reaction to happen. Enzymes lower the activation energy needed for a reaction to happen. Enzymes are so reactive that they speed up less reactive molecules. Enzymes add small amounts of energy to make a reaction happen.