Question

Which of the following statements are TRUE for hexokinase and glucokinase?

• A. They are both ubiquitously present in all cells
• B. They are isozymes
• C. They differ in their \( K_m \) for glucose
• D. They are identical in their primary structure

Hint:

Hexokinase and glucokinase are both enzymes that catalyze the phosphorylation of glucose, but their differences in \( K_m \) and tissue distribution are key to their distinct physiological roles.

Answer 1

The Correct Option is B, C

Step 1: Understanding hexokinase and glucokinase.
Hexokinase and glucokinase are two different enzymes involved in glucose metabolism. Hexokinase is found in almost all tissues and has a low \( K_m \) for glucose, meaning it has a high affinity for glucose. Glucokinase, however, is found in the liver and pancreas and has a higher \( K_m \), indicating a lower affinity for glucose.

Step 2: Analyzing the options.
(A) They are both ubiquitously present in all cells: This is incorrect. While hexokinase is found in nearly all tissues, glucokinase is primarily present in the liver and pancreas.
(B) They are isozymes: This is correct in a sense, as they catalyze the same reaction but differ in their properties and tissue distribution. However, this option doesn't explain the difference between hexokinase and glucokinase in terms of \( K_m \).
(C) They differ in their \( K_m \) for glucose: This is correct. Hexokinase has a lower \( K_m \) than glucokinase, reflecting their different affinities for glucose.
(D) They are identical in their primary structure: This is incorrect. Hexokinase and glucokinase have different primary structures, even though they perform similar functions.

Step 3: Conclusion.
The correct answer is (C) They differ in their \( K_m \) for glucose, as this directly explains the key functional difference between hexokinase and glucokinase.