Final answer:
Transcription factors determine protein presence by binding to cis-acting elements, such as the promoter, enhancers, and specific DNA sequences, regulating gene transcription. Epigenetic modifications and environmental stimuli can also influence transcription factor activity, impacting gene expression and protein synthesis.
Step-by-step explanation:
The accessibility of cis-acting elements to the trans acting factors, such as transcription factors, is determined by the chromatin structure and the presence of specific epigenetic marks. Transcription factors bind to cis elements like promoter-proximal elements, enhancers, and the TATA box to regulate the transcription of adjacent genes. When transcription factors are bound to these regulatory elements, it allows for the recruitment of the general transcription machinery and modulation of gene expression. Environmental stimuli can affect transcription factor activity, which in turn determines the presence of particular proteins in a cell through initiating or repressing gene transcription.
For instance, hormone receptors, which are also transcription factors, can bind to cis-acting transcription control elements to regulate the transcription of genes pertinent to hormonal signaling. Mutations in cis elements like promoters can disrupt transcription factor binding, leading to altered gene expression. Ultimately, through a dynamic interplay with epigenetic modifications such as DNA methylation and histone acetylation, transcription factors play a crucial role in determining whether a protein is produced in a given cell.