How is gene expression regulation described as differing between bacteria and eukaryotes?

• A. In bacteria, promoters and enhancers regulate gene expression; in eukaryotes, operons regulate gene expression.
• B. In bacteria, gene expression is regulated exclusively at the DNA sequence level; in eukaryotes, there is no regulation.
• C. In bacteria, operons regulate gene expression; in eukaryotes, promoters, enhancers, transcription factors, and epigenetic modifications regulate gene expression.
• D. In both domains, only post-transcriptional controls regulate gene expression.

Answer: (C)

Differing organization of genomes leads to distinct regulatory strategies in bacteria and eukaryotes. In bacteria, genes that work together are often grouped into operons under a single promoter, so regulation centers on turning transcription on or off at that promoter in response to signals. Repressor proteins or activators bind near the promoter or operator to coordinate the expression of multiple genes at once, enabling rapid, simple control of related functions.

In contrast, eukaryotic regulation is more layered and versatile. Genes are typically controlled by promoters that recruit transcription machinery, but nearby enhancers (which can be far away) also modulate transcription through looping interactions with transcription factors. In addition, transcription factors themselves, as well as chromatin state governed by epigenetic modifications like histone marks and DNA methylation, shape whether a gene is accessible for transcription. This combination allows nuanced, cell-type–specific, and developmentally regulated expression patterns.

So the best description is that bacteria use operons to coordinate gene expression under a single promoter, while eukaryotes employ promoters, enhancers, transcription factors, and epigenetic changes to regulate gene expression. Post-transcriptional controls exist in both domains, but they don’t capture the primary regulatory differences between them.