Question

Cell biologists have introduced radioactively labeled carbohydrates, fats and amino acids to living cells, allowed time for cell metabolism, and then disrupted the cells in a blender and separated out the various cell organelles from the cytoplasm. They found the radioactive molecules could soon be detected as part of various cellular compounds, although the visible cell structures appeared unchanged. This leads us to conclude that

A. these "food" molecules are used only for energy.
B. most cell components are constantly being broken down and rebuilt.
C. radioactivity was transferred from the introduced molecules to the resident stable molecules.
D. molecules diffuse at random through the cytoplasm and into cell organelles.
E. radioactivity has an unusual role in metabolism of living cells.

Answer 1

Radioactive labeling of molecules like amino acids allows researchers to trace cellular metabolic pathways and demonstrate that cell components break down and rebuild constantly. Radioactivity is first evident in ribosomes, followed by the Golgi apparatus and ER. Radioisotopes are valuable tools in both research and medical diagnostics but come with health concerns.

Step-by-step explanation:

The introduction of radioactively labeled molecules such as carbohydrates, fats, and amino acids into living cells is a technique used to trace the pathways of cellular metabolism. This process, known as a pulse, involves following the appearance of radioactive proteins within the cell compartments. The radioactivity appears first in the ribosomes, as these are the sites of protein synthesis where amino acids are assembled into proteins. Subsequently, radioactivity becomes evident in the Golgi apparatus and endoplasmic reticulum (ER), where proteins are processed and transported. The inclusion of radioactive molecules allows for in-depth analysis of cellular processes such as the synthesis, modification, and transportation of molecules. It demonstrates that components within the cell are dynamically managed, breaking down and reforming constantly in the service of the cell's metabolic needs. Despite the introduction of radioactivity, the visible structures of the cells remain unchanged, indicating that these components are part of a regular physiological process rather than causing any anomalous effects.

The versatility of radioisotopes in studying biological systems is reflected not only in research settings but also in medical applications like PET scans, where they help visualize metabolic activity in body tissues. However, there's a cautious approach to their use due to potential biological damage caused by high-energy emissions and the need to manage their impact on health and the environment efficiently.