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.


If Pseudomonas bacteria are supplied with radioactively labeled cytosine, after a 24-hour incubation period this cytosine would most likely be found in the cells’
a. carbohydrates.
b. DNA.
c. lipids.
d. water.
e. proteins.

Verified step by step guidance

1. Understand the structure of cytosine: Cytosine is one of the four main bases found in DNA and RNA, which are nucleic acids.
2. Identify the role of cytosine in the cell: Cytosine is a pyrimidine base that pairs with guanine in DNA and RNA, forming part of the genetic code.
3. Consider the macromolecules in the cell: The main macromolecules are carbohydrates, lipids, proteins, and nucleic acids (DNA and RNA).
4. Determine where cytosine is incorporated: Since cytosine is a nucleic acid base, it is incorporated into DNA and RNA, not into carbohydrates, lipids, or proteins.
5. Conclude the most likely location of labeled cytosine: Given its role as a nucleic acid base, the radioactively labeled cytosine would most likely be found in the DNA of the Pseudomonas bacteria after incubation.

Key Concepts

Nucleic Acids and Their Components

Cytosine is one of the four nucleobases in nucleic acids, specifically DNA and RNA. Understanding the structure and function of nucleic acids is crucial, as they are responsible for storing and transmitting genetic information. When Pseudomonas bacteria are supplied with labeled cytosine, it is expected to be incorporated into their nucleic acids, particularly DNA.

Metabolic Pathways

Metabolic pathways are series of chemical reactions occurring within a cell that convert substrates into products. In the case of cytosine, bacteria can utilize it in various metabolic processes, including the synthesis of nucleotides, which are essential for DNA and RNA synthesis. Recognizing how cells metabolize different molecules helps predict where labeled compounds will end up.

Radioisotope Tracing

Radioisotope tracing is a technique used to track the movement and incorporation of specific atoms within biological systems. By using radioactively labeled molecules, researchers can follow the fate of these molecules in cellular processes. In this scenario, the radioactively labeled cytosine allows for the observation of its incorporation into cellular components, aiding in understanding cellular metabolism.