Glycolysis is the conversion of glucose into pyruvate to generate energy in the form of adenine triphosphate (ATP). The 1st step of glycolysis is the conversion of glucose to glucose-6-phosphate and by transferring a phosphate group from ATP and forming ADP. This reaction requires the enzyme hexokinase, which is found in all multicellular organisms. In this video, we will show how the overall structure of hexokinase changes upon binding its substrate glucose and show how the shape of the activate site accommodates and positions both the ATP and glucose molecules for a chemical reaction to occur.