Transcription Factors and Epigenetic Control
Transcription factors bind DNA and decide which genes are read, while methylation and histone changes decide which genes can be reached at all. Both are reversible and neither alters the base sequence.
What a learner can do afterwards
- Explains how a transcription factor changes the rate at which a gene is transcribed.
- Distinguishes a change in DNA methylation from a change in the DNA sequence.
- Links a heritable change in expression to chromatin state rather than to mutation.
1 · Read
Almost every cell in your body holds the same genes, yet a liver cell and a nerve cell behave nothing alike. The answer is control: each cell type reads a different set of chapters from the same book. Control starts with whether the reading machinery can even reach a gene, and several layers tune that access.
Transcription factors are proteins that bind DNA near a gene and set how keenly it fires. Activators help RNA polymerase dock at the promoter and begin, while repressors block the site or stall the machinery. A gene often listens to several factors at once, so its output reflects the mix of signals in that cell.
Epigenetic marks decide which genes can be reached at all, without touching the letters. Methyl groups stuck onto DNA usually hush a gene, and removing them can switch it back on. DNA winds round histone proteins into chromatin: tight packing hides genes while loose packing exposes them, and acetyl groups loosen the packing so the machinery can reach in.
Sort an epigenetic change from a mutation with one test: did the sequence change. An epigenetic mark passes to daughter cells while the base sequence stays identical, so the volume knob moves and stays moved. A mutation rewrites the letters themselves. Liver and nerve cells differ by marks and factors, not by owning different genomes.
Factors set the transcription rate and epigenetic marks set the access, all without rewriting DNA.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.