The enzyme hexokinase catalyzes the conversion of glucose to glucose-6-phosphate,which is an important step in glycolysis. The reaction involves the transfer of a phosphate group from ATP to glucose.Either a glucose molecule or a water molecule can fit in the active site of hexokinase. The presence of a water molecule in hexokinase’s active site would result in the hydrolysis of ATP to ADP instead of the conversion of glucose to glucose-6-phosphate. Which of the following statements best helps explain the reaction specificity of hexokinase?a. Both glucose and water are polar molecules that form favorable interactions with charged and polar amino acid side chains in hexokinase’s active site.b. Both glucose and water have oxygen atoms that can form covalent bonds with the phosphorus atoms of phosphate groups.c. Glucose is an energy-rich organic molecule that can be broken down by glycolysis to produce ATP, whereas water is an inorganic molecule.d. Glucose has the right shape and charge to cause hexokinase to undergo a structural change needed for catalysis, whereas water does not.

d is the correct option. It explains the reaction specificity of hexokinase during glycolysis. Glycolysis is the metabolic pathway in which glucose is converted to pyruvate to generate a high energy molecule in the form of ATP and NADH.

In the first step of glycolysis, glucose (6-carbon ring) is catalyzed to glucose-6-phosphate by Hexokinase enzyme using Mg-adenosine triphosphate (Mg-ATP) as a source of phosphate. Hexokinase demonstrates conformational change on binding site in glucose. Precisely, it brings C6-OH group of glucose and Mg-ATP close and binds together at the active site. This bond excludes water (H2O) from the active site. The active site has the capability to bind two ligands, glucose, and glucose-6-phosphate. When glucose binds, hexokinase goes through an induced-fit conformational change that prevents the hydrolysis of ATP.

Final impression: Such a catalysis is specified to hexokinase, and cannot be done by any other molecule. Glucose has the right shape and charge to cause hexokinase to undergo a structural change needed for catalysis, whereas other molecule is not suitable for this reaction.