This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Which is not a common enzyme for glycolysis and gluconeogenesis? 
Select and explain. 
A. Aldolase, B. Glucose-6-phosphatase, C. Phosphoglycerate mutase, D. Phosphoglycerate kinase
B: Glucose-6-phosphatase
Answer: B: Glucose-6-phosphatase 
Explanation: Seven of the reactions of glycolysis are reversible and are used in the synthesis of glucose by gluconeogenesis. Thus, seven enzymes are common to both glycolysis and gluconeogenesis : (i) Phosphohexose isomerase; (ii) Aldolase; (iii) Phosphotriose isomerase, (iv) Glyceraldehyde 3-phosphate dehydrogenase; (v) Phosphoglycerate kinase; (vi) Phosphoglycerate mutase; (vii) Enolase. Three reactions of glycolysis are irreversible which are circumvented in gluconeogenesis by four reactions. So, enzymes at these steps are different in glycolysis and gluconeogenesis.