Do transcription factors always turn genes fully “on” or “off”?

Not usually. In IB Biology, it’s safer to describe transcription factors as shifting the probability and rate of transcription. Activators can increase how often RNA polymerase initiates transcription, while repressors can reduce that frequency. Many genes are regulated by multiple transcription factors at once, so the outcome is often “more” or “less,” not absolute. This is why exam questions sometimes mention “increase in transcription rate” rather than a simple switch. If you include chromatin accessibility, your answer becomes more realistic and higher-scoring. RevisionDojo’s Study Notes help you practice that precise wording until it feels automatic.

How do transcription factors know where to bind on DNA?

They bind using DNA-binding domains that recognize specific base sequences (motifs) typically in promoters, enhancers, or silencers. The important IB Biology idea is specificity: a transcription factor has a shape and chemical pattern that matches certain DNA sequences. These sequences act like docking sites, often called response elements. Once bound, the transcription factor can recruit or block other proteins involved in transcription. This is also why signals can activate only certain genes, not the whole genome. If you want extra clarity, pair this with active recall using RevisionDojo Flashcards.

How do signals like hormones change gene expression through transcription factors?

Signals can activate transcription factors by changing their shape, location, or phosphorylation state. In IB Biology, a classic example is steroid hormones that diffuse into cells and bind intracellular receptors. The hormone-receptor complex can act as a transcription factor, binding DNA and changing transcription. Other signals work through cell-surface receptors and cascades that activate transcription factors indirectly. This lets the cell connect the environment to gene expression without changing the DNA sequence. It’s a powerful mechanism because it’s fast, reversible, and gene-specific. RevisionDojo’s AI Chat can help you practise explaining this clearly for different command terms.