Question

The liver enzyme glucokinase catalyzes the

phosphorylation of glucose to glucose 6-phosphate.
The value of Km for glucose is about 7 mM. Blood glucose is 5 mM under fasting conditions, and can rise in the liver to 20 mM after a high-carbohydrate meal. Therefore, if a
person who is fasting eats a high-carbohydrate
meal, the velocity of the glucokinase reaction
will change in which one of the following ways?
(A) Remain at <50% Vmax
(B) Remain above 80% Vmax
(C) Increase from <50% Vmax to >50% Vmax
(D) Decrease from >50% Vmax to <50% Vmax
(E) Remain at Vmax

Answer 1

After a high-carbohydrate meal, the velocity of the glucokinase reaction in a person who is fasting will increase from <50% Vmax to >50% Vmax.

So, the correct answer is C) Increase from <50% Vmax to >50% Vmax.

Step-by-step explanation:

The liver enzyme glucokinase plays a crucial role in the metabolism of glucose, catalyzing the phosphorylation of glucose to glucose 6-phosphate. This process is a part of glycolysis, where glucose is trapped within cells and then used or stored. The Km, or the Michaelis constant, for glucose, is about 7 mM, indicating the affinity of the enzyme for its substrate.

Under fasting conditions, when the blood glucose level is 5 mM, glucokinase functions below its Km, and as a result, the reaction velocity is less than 50% of Vmax (the maximum rate of the enzymatic reaction). When a high-carbohydrate meal is eaten, blood glucose levels can rise to 20 mM, surpassing the Km value.

Since the glucose concentration now exceeds the Km, the rate of the reaction will increase and the velocity of glucokinase will rise to more than 50% of Vmax. It does not, however, reach Vmax because the enzyme would require even higher levels of glucose to achieve that.

Thus, the correct answer is: (C) Increase from <50% Vmax to >50% Vmax.