What controls gene expression at the transcription level?

• A. Ribosomes and tRNA.
• B. Transcription factors, promoters, enhancers, and regulatory proteins.
• C. DNA replication enzymes.
• D. Mitochondrial enzymes.

Answer: (B)

Control of gene expression at the transcription level relies on DNA elements and proteins that determine whether RNA polymerase can start making mRNA. Promoters provide the binding site for RNA polymerase and general transcription factors to initiate transcription. Transcription factors and regulatory proteins act as activators or repressors, interpreting cellular signals and binding to promoter or nearby enhancer regions. Enhancers are distal DNA sequences that boost transcription by looping to the promoter and recruiting the transcription machinery, increasing mRNA production. Together, these components shape how much of a gene’s mRNA is produced, setting the level of gene expression from the start. By contrast, ribosomes and tRNA function in translation, DNA replication enzymes copy DNA, and mitochondrial enzymes aren’t directly about regulating transcription of nuclear genes.