Which statement best describes the scope of regulation in eukaryotic gene expression?

• A. All genes are expressed at a constant rate in eukaryotes
• B. Protein synthesis is the only level of gene expression control
• C. Regulation can occur at transcription, mRNA stability, export, and translation
• D. Post-translational modifications are not involved in regulation

Answer: (C)

In eukaryotes, regulation of gene expression happens at several different stages, not just one. A gene’s activity can be controlled at the level of transcription, where many factors decide whether the RNA polymerase should start making the transcript. After transcription, the stability of the mRNA influences how long the message persists; transcripts can be quickly degraded or stabilized by RNA-binding proteins and microRNAs, affecting how much protein is produced. The cell can also regulate whether an mRNA is exported from the nucleus to the cytoplasm, so only transcripts that are properly processed and allowed to exit can be translated. Finally, translation itself is controlled: initiation and efficiency of ribosome binding determine how much protein is synthesized from a given mRNA.

This option correctly highlights regulation across transcription, mRNA stability, export, and translation, which together cover the major control points used by cells to fine-tune gene expression. It’s understood that additional layers exist—such as post-translational modifications that modify protein activity after synthesis—but the statement still best describes the wide range of regulatory steps available in eukaryotes. The other choices are incorrect because genes are not expressed at a constant rate, regulation extends beyond translation, and post-translational modifications do play regulatory roles.