Both water and glucose share an -OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by hexokinase. Glucose, however, is about a million times more reactive as a substrate than water. The BEST explanation is that:
A) glucose has more -OH groups per molecule than does water.
B) the larger glucose binds better to the enzyme; it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis.
C) the -OH group of water is attached to an inhibitory H atom, while the glucose -OH group is attached to C.
D) water and the second substrate, ATP, compete for the active site resulting in a competitive inhibition of the enzyme.
E) water normally will not reach the active site because it is hydrophobic.

Question

Quizplus · Accepted Answer

The larger size and shape of glucose allows it to bind better to hexokinase and induce a conformational change that brings active-site amino acids into position for catalysis. This increases the reactivity of glucose as a substrate compared to water. The number of -OH groups per molecule (A) and the attachment of -OH groups to C vs. H (C) are not relevant factors in the difference in reactivity between glucose and water. There is no evidence of competitive inhibition (D) or exclusion by hydrophobicity (E) in this scenario.

Both Water and Glucose Share an -OH That Can Serve