Transcription factors are proteins that regulate the transcription of genes.

• A. Proteins that regulate transcription of genes.
• B. Lipids that form membranes that regulate gene expression.
• C. Enzymes that splice mRNA.
• D. Carbohydrates that store energy.

Answer: (A)

Transcription factors are regulatory proteins that control transcription. They bind specific DNA sequences in promoters or enhancers and help recruit or block RNA polymerase II, so they can increase or decrease the amount of RNA produced from a gene. This direct role in turning genes on or off is what the statement is capturing. Other options describe molecules with different jobs: lipids form membranes and don’t directly regulate transcription; enzymes that splice mRNA act during RNA processing after transcription; carbohydrates store energy and aren’t involved in initiating transcription. Transcription factors can be general players needed for transcription or specific factors that respond to signals to fine-tune gene expression.