Certain radioactively labeled compounds, like 32 P-labeled ATP, are unsuitable for whole cell studies because they fail to penetrate cell membranes. The presence of a radioactive isotope does not alter the chemical properties of a molecule, meaning that if a compound cannot enter cells in its non-labeled form, it will not do so when labeled. This raises questions about the accuracy of claims regarding the compound's cellular entry. The discussion emphasizes the importance of understanding the inherent properties of compounds, regardless of labeling, to ensure accurate experimental design and interpretation in cellular studies.