Ch. 2 - Chemical Principles

Tortora - Microbiology: An Introduction 14th Edition

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Tortora 14th Edition

Ch. 2 - Chemical Principles

Problem 2

Chapter 2, Problem 2

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 the following question.

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

Step 1: Understand the role of cytosine in cellular molecules. Cytosine is one of the four nitrogenous bases found in nucleic acids, specifically DNA and RNA.

Step 2: Recall that cytosine is not a component of carbohydrates, lipids, water, or proteins. These macromolecules have different building blocks: carbohydrates are made of sugars, lipids of fatty acids and glycerol, proteins of amino acids, and water is a simple molecule (H2O).

Step 3: Since cytosine is a nitrogenous base, it is incorporated into nucleic acids. In bacteria like Pseudomonas, DNA contains cytosine as part of its structure.

Step 4: When bacteria are supplied with radioactively labeled cytosine, the label will be incorporated into newly synthesized DNA molecules during replication or repair processes.

Step 5: Therefore, after incubation, the radioactive cytosine will most likely be found in the cells' DNA.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Role of Cytosine in Cellular Molecules

Cytosine is one of the four nitrogenous bases found in nucleic acids, specifically DNA and RNA. It pairs with guanine in DNA, making it a fundamental component of genetic material rather than carbohydrates, lipids, or proteins.

Radioisotope Labeling in Microbiology

Radioisotope labeling involves incorporating radioactive atoms into molecules to trace their path and fate within cells. This technique helps identify where specific molecules, like cytosine, are utilized or incorporated over time.

Macromolecular Composition of Cells

Cells are composed of major macromolecules: nucleic acids, proteins, lipids, and carbohydrates. Each has distinct building blocks; nucleic acids contain nitrogenous bases like cytosine, while proteins, lipids, and carbohydrates do not incorporate cytosine.

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Related Practice

Textbook Question

What type of bond holds the following atoms together?

a. Li⁺ and Cl^- in LiCl

b. Carbon and oxygen atoms in methanol

c. Oxygen atoms in O₂

d. A hydrogen atom of one nucleotide to a nitrogen or oxygen atom of another nucleotide in:

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Textbook Question

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 the following question.

If E. coli were grown in a medium containing the radioactive isotope ³²P, the ³²P would be found in all of the following molecules of the cell except

a. ATP.

b. Carbohydrates.

c. DNA.

d. Plasma membrane.

e. Complex lipids.

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Textbook Question

What is a chemical element?

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Textbook Question

Diagram the electronic configuration of a carbon atom.

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Textbook Question

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 the following question.

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

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