- Chosen by Voters In chemistry, a substrate is a reactant acted upon by an enzyme (a protein that makes the reaction run faster). Reactants are the starting materials of a reaction and will always be on the left side of the equation. The products will be on the right side. Some examples are:CH4 + 2 O2 –> CO2 + 2 H2O the oxidation of methane (CH4 is a reactant) to carbon dioxide (CO2 is a product). Oxygen is also a reactant and water is another product.C6H12O6 –hexokinase–> C6H12O6PO4The conversion of glucose (substrate) to glucose-6-phosphate (product) with hexokinase (an enzyme) in the glycolysis pathway. Source(s): I am a molecular biology student and I completed my Cell Biology courses last fall. 3 years ago 100% 1 Vote