Cell Biologists Have Introduced Radioactively Labeled Carbohydrates, Fats and Amino

question 10

Multiple Choice

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.

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