Advanced Placement (AP) Biology Practice Exam

What is a transcription factor?

1. A regulatory protein that binds to DNA

2. A type of hormone

3. A signaling molecule

4. A cellular receptor

The correct answer is: A regulatory protein that binds to DNA

A transcription factor is a regulatory protein that plays a crucial role in gene expression. Its primary function is to bind to specific DNA sequences, typically in the promoter region of a gene, thereby influencing the transcription of that gene into messenger RNA (mRNA). By binding to DNA, transcription factors can either promote or inhibit the recruitment of RNA polymerase, the enzyme responsible for synthesizing RNA from a DNA template, thereby controlling the rate at which genes are expressed. Transcription factors can also interact with other proteins and regulatory molecules to form complexes that are essential for the precise regulation of gene activity. They respond to cellular signals, helping the cell adapt to various conditions by turning specific genes on or off as needed. This control over gene expression is fundamental for processes such as development, cellular differentiation, and responses to environmental changes, making transcription factors vital components in the regulation of cellular functions.