Question

The phosphopentose epimerase converts ribulose 5-P to xylulose 5-P:

a) During glycolysis
b) In the Calvin cycle
c) In the pentose phosphate pathway
d) During gluconeogenesis

Answer 1

The phosphopentose epimerase converts ribulose 5-P to xylulose 5-P in the pentose phosphate pathway, which functions parallel to glycolysis and is crucial for generating NADPH and five-carbon sugars necessary for nucleotide synthesis.

Step-by-step explanation:

The enzyme phosphopentose epimerase converts ribulose 5-phosphate (ribulose 5-P) to xylulose 5-phosphate (xylulose 5-P) in the pentose phosphate pathway (PPP). This pathway is known by several names, including the phosphogluconate pathway or the hexose monophosphate shunt. It operates parallel to glycolysis and serves a critical role in cells by generating NADPH and five-carbon sugars, including ribose 5-phosphate which is essential for nucleotide synthesis. Unlike glycolysis that primarily focuses on the breakdown of glucose for energy, the PPP is important for its role in biosynthesis, particularly when the cell has a need for nucleic acid and protein synthesis. Therefore, the correct option for where the phosphopentose epimerase functions is (c) In the pentose phosphate pathway.