Radioisotopes are frequently used to label molecules in a cell. The fate of atoms and molecules in a cell can then be followed. This process is the basis for questions 1-3.


Assume E. coli bacteria are grown in a nutrient medium containing the radioisotope ¹⁶N. After a 48-hour incubation period, the ¹⁶N would most likely be found in the E. coli’s
a. carbohydrates.
b. lipids.
c. proteins.
d. water.
e. none of the above

Verified step by step guidance

1. Understand that radioisotopes are used to trace the incorporation of specific atoms into cellular components.
2. Recognize that ¹⁶N is a nitrogen isotope, and nitrogen is a key element in certain biological molecules.
3. Recall that proteins are composed of amino acids, which contain nitrogen in their amino groups.
4. Consider that carbohydrates and lipids primarily consist of carbon, hydrogen, and oxygen, with little to no nitrogen.
5. Conclude that the radioisotope ¹⁶N would most likely be incorporated into proteins, as they are the primary nitrogen-containing macromolecules in cells.

Key Concepts

Radioisotopes in Biological Research

Radioisotopes, such as ¹⁶N, are unstable isotopes that emit radiation as they decay. In microbiology, they are used to trace the incorporation of specific atoms into biological molecules, allowing researchers to study metabolic pathways and cellular processes. By labeling molecules with radioisotopes, scientists can track their fate within cells, providing insights into how organisms utilize nutrients.

Nitrogen's Role in Biomolecules

Nitrogen is a crucial element found in amino acids, nucleotides, and other biomolecules. In E. coli, nitrogen from the nutrient medium is incorporated into proteins and nucleic acids, which are essential for growth and reproduction. Understanding how nitrogen is assimilated into these molecules helps explain the metabolic functions of bacteria and their growth requirements.

Metabolic Pathways in E. coli

E. coli utilizes various metabolic pathways to synthesize biomolecules from available nutrients. When grown in a medium containing ¹⁶N, the bacteria will incorporate this nitrogen into proteins, nucleic acids, and other nitrogen-containing compounds. Recognizing these pathways is essential for predicting where the labeled nitrogen will be found after incubation, as it reflects the organism's metabolic activity and nutrient utilization.