Final answer:
Transcription factors are proteins that control gene expression by promoting or inhibiting the binding of RNA polymerase to genes, thus playing a pivotal role in cellular differentiation and response to environmental cues.
Step-by-step explanation:
Transcription factors are proteins that regulate the process of transcription, which is the first step in gene expression. They play a crucial role by affecting the binding of RNA polymerase to a particular gene on the DNA molecule. These factors can either promote or inhibit transcription, thus essentially turning genes 'on' or 'off.' Basal transcription factors, for instance, are essential for the formation of a preinitiation complex that recruits RNA polymerase II, while other transcription factors bind to enhancers and silencers to modulate the frequency of transcription.
In a cellular context, transcription factors allow cells to perform their specialized functions by controlling which genes are expressed and which remain silent. They respond to environmental stimuli and bind specifically to DNA sequences known as transcription factor binding sites, present on promoters or enhancers, thereby governing the transcription of necessary genes.