Glutamine is a vital fuel for rapidly dividing cells. Which of the following statements best describes one of these cell types that utilizes glutamine as an energy source?

• A. It is primarily a signaling molecule for appetite suppression.
• B. It serves as a vital fuel for rapidly dividing cells such as enterocytes, fibroblasts, reticuloendothelial cells and malignant cells.
• C. It functions as the main energy source for red blood cells.
• D. It is an essential vitamin.

Answer: (B)

Glutamine serves as an important energy and biosynthetic substrate for rapidly dividing cells, which is why the statement describing these cells—enterocytes in the gut, fibroblasts, reticuloendothelial cells, and many malignant cells—as using glutamine as a vital fuel best fits. Mechanistically, glutamine is taken up by cells and converted first to glutamate, then to alpha-ketoglutarate, feeding the TCA cycle to generate ATP and provide carbon backbones for nucleotides and other biosynthetic needs. This makes glutamine especially important for tissues with high turnover or rapid growth.

Other options don’t align with this primary role. Glutamine is not recognized mainly as a signaling molecule for appetite suppression. Red blood cells rely primarily on glycolysis of glucose for energy and do not use glutamine as their main energy source. And glutamine is an amino acid, not a vitamin.