AAMC FL Practice Exam

What describes an operon in prokaryotic cells?

1. A single gene transcribed from multiple promoters

2. Two genes transcribed from multiple promoters

3. A cluster of genes transcribed from a single promoter

4. One gene transcribed from a single promoter

The correct answer is: A cluster of genes transcribed from a single promoter

An operon in prokaryotic cells refers to a genetic unit consisting of a cluster of genes that are transcribed together from a single promoter. This arrangement allows for the coordinated expression of genes that often participate in the same metabolic pathway or function. By being regulated as a single unit, operons enable cells to efficiently manage the production of proteins required for specific biological processes, responding to environmental changes and conserving resources. For example, the well-studied lac operon in E. coli contains genes necessary for the metabolism of lactose, including genes coding for proteins that transport lactose into the cell and enzymes that break it down. The entire operon is regulated by a single promoter, making it energetically favorable for the bacterial cell to produce all necessary proteins simultaneously when lactose is present. Understanding this concept is crucial in the study of prokaryotic gene expression, highlighting how bacteria can efficiently control the synthesis of multiple proteins that work together in a single functional pathway.