MCAT Biochemistry Question 135: Answer and Explanation
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Question: 135
15. Each of the following catalyzes a rate-limiting step of a carbohydrate metabolism pathway EXCEPT:
- A. hexokinase.
- B. glycogen synthase.
- C. glucose-6-phosphate dehydrogenase.
- D. fructose-1,6-bisphosphatase.
Correct Answer: A
Explanation:
Hexokinase catalyzes an important irreversible step of glycolysis, but it is not the rate-limiting step. Phosphofructokinase-1 catalyzes the rate-limiting step of glycolysis. Glycogen synthase (choice (B)) catalyzes the rate-limiting step of glycogenesis, glucose-6-phosphate dehydrogenase (choice (C)) catalyzes the rate-limiting step of the pentose phosphate pathway, and fructose-1,6-bisphosphatase (choice (D)) catalyzes the rate-limiting step of gluconeogenesis.