Metabolic pathways: the pentose phosphate pathway (also called the phosphogluconate pathway or hexose monophosphate shunt) occurs in which types of cells?

Introduction / Context:
The pentose phosphate pathway (PPP) is a ubiquitous metabolic route that generates NADPH for reductive biosynthesis and ribose-5-phosphate for nucleotide synthesis. Knowing its distribution across life forms emphasizes its fundamental role.

Given Data / Assumptions:

• PPP provides NADPH and pentose sugars in many organisms.
• It functions in parallel with glycolysis, with both oxidative and nonoxidative branches.
• Cell type options include prokaryotes and eukaryotes.

Concept / Approach:
The PPP is present in both prokaryotic and eukaryotic cells. In eukaryotes, it is prominent in the cytosol, especially in tissues requiring high NADPH (e.g., liver, adipose, adrenal cortex, and red blood cells). In bacteria, it supports biosynthesis and oxidative stress defense.

Step-by-Step Solution:

Verification / Alternative check:
Genomic and biochemical studies show PPP genes in bacteria and eukaryotes; clinical relevance includes G6PD deficiency affecting the oxidative branch in human RBCs.

Why Other Options Are Wrong:
Prokaryotic only / Eukaryotic only: Too narrow; PPP is widespread. None of these: False because PPP clearly exists.

Common Pitfalls:
Assuming PPP is “alternative” and rare; in fact, it is central for NADPH and nucleotide biosynthesis in many cell types.

Final Answer:
prokaryotic and eukaryotic cells both